<PAGE>

                                                                     Exhibit 4.1
================================================================================

                          ALEXION PHARMACEUTICALS, INC.

                                       and

                            THE CHASE MANHATTAN BANK
                                       as
                                     Trustee

                         -------------------------------

                                    INDENTURE

                            Dated as of March 8, 2000

                         -------------------------------

                         $ 120,000,000 Principal Amount*

                 5 3/4% CONVERTIBLE SUBORDINATED NOTES DUE 2007

================================================================================

----------------
*     Plus an additional $30,000,000 issuable at the option of the Initial
      Purchasers as described herein.
<PAGE>

                              CROSS-REFERENCE TABLE

    TIA                                                      Indenture
  Section                                                     Section
  -------                                                     -------

   310(a)(1) ..............................................   7.10
      (a)(2) ..............................................   7.10
      (a)(3) ..............................................   N.A.
      (a)(4) ..............................................   N.A.
      (a)(5) ..............................................   N.A.
      (b) .................................................   7.08; 7.10; 13.02
      (c) .................................................   N.A.
   311(a) .................................................   7.11
      (b) .................................................   7.11
      (c) .................................................   N.A.
   312(a) .................................................   2.05
      (b) .................................................   13.03
      (c) .................................................   13.03
   313(a) .................................................   7.06
      (b)(1) ..............................................   N.A.
      (b)(2) ..............................................   7.06
      (c) .................................................   7.06; 13.02
      (d) .................................................   7.06
   314(a) .................................................   4.02
      (b) .................................................   N.A.
      (c)(1) ..............................................   13.04
      (c)(2) ..............................................   13.04
      (c)(3) ..............................................   N.A.
      (d) .................................................   N.A.
      (e) .................................................   13.05
      (f) .................................................   N.A.
   315(a) .................................................   7.01(b)
      (b) .................................................   7.05; 13.02
      (c) .................................................   7.01(a)
      (d) .................................................   7.01(c)
      (e) .................................................   6.11
   316(a)(last sentence) ..................................   2.09
      (a)(1)(A) ...........................................   6.05
      (a)(1)(B) ...........................................   6.04
      (a)(2) ..............................................   N.A.
      (b) .................................................   6.07
   317(a)(1) ..............................................   6.08
      (a)(2) ..............................................   6.09
      (b) .................................................   2.04
   318(a) .................................................   13.01
<PAGE>

                                TABLE OF CONTENTS
                                                                         Page
                                                                         ----

                                       ARTICLE ONE

                        DEFINITIONS AND INCORPORATION BY REFERENCE

SECTION 1.01.   Definitions .............................................  1
SECTION 1.02.   Other Definitions .......................................  5
SECTION 1.03.   Incorporation by Reference of Trust Indenture Act .......  6
SECTION 1.04.   Rules of Construction ...................................  6

                                   ARTICLE TWO

                                 THE SECURITIES

SECTION 2.01.   Form and Dating .........................................  7
SECTION 2.02.   Execution and Authentication ............................  7
SECTION 2.03.   Registrar, Paying Agent and Conversion Agent ............  8
SECTION 2.04.   Paying Agent to Hold Money in Trust .....................  8
SECTION 2.05.   Securityholder Lists ....................................  9
SECTION 2.06.   Transfer and Exchange ...................................  9
SECTION 2.07.   Replacement Securities ..................................  9
SECTION 2.08.   Outstanding Securities .................................. 10
SECTION 2.09.   Securities Held by the Company or an Affiliate .......... 10
SECTION 2.10.   Temporary Securities .................................... 10
SECTION 2.11.   Cancellation ............................................ 10
SECTION 2.12.   Defaulted Interest ...................................... 11
SECTION 2.13.   CUSIP Numbers ........................................... 11
SECTION 2.14.   Deposit of Moneys ....................................... 11
SECTION 2.15.   Book-Entry Provisions for Global Securities ............. 11
SECTION 2.16.   Special Transfer Provisions ............................. 12
SECTION 2.17.   Restrictive Legends ..................................... 15

                                  ARTICLE THREE

                             REDEMPTION; REPURCHASE

SECTION 3.01.   Notices to Trustee ...................................... 15
SECTION 3.02.   Selection of Securities to Be Redeemed .................. 16
SECTION 3.03.   Notice of Redemption .................................... 16
SECTION 3.04.   Effect of Notice of Redemption .......................... 17
SECTION 3.05.   Deposit of Redemption Price ............................. 17
SECTION 3.06.   Securities Redeemed in Part ............................. 17
SECTION 3.07.   Repurchase at Option of Holder upon a Repurchase Event .. 18


                                       -i-
<PAGE>

                                                                         Page
                                                                         ----

                                       ARTICLE FOUR

                                        COVENANTS

SECTION 4.01.   Payment of Securities ................................... 23
SECTION 4.02.   Maintenance of Office or Agency ......................... 23
SECTION 4.03.   Reports to Holders ...................................... 24
SECTION 4.04.   Compliance Certificate .................................. 24
SECTION 4.05.   Stay, Extension and Usury Laws .......................... 24
SECTION 4.06.   Corporate Existence ..................................... 24
SECTION 4.07.   Notice of Default ....................................... 25

                                  ARTICLE FIVE

                    CONSOLIDATION, MERGER AND SALE OF ASSETS

SECTION 5.01.   When Company May Merge, etc. ............................ 25
SECTION 5.02.   Successor Substituted ................................... 25

                                   ARTICLE SIX

                              DEFAULTS AND REMEDIES

SECTION 6.01.   Events of Default ....................................... 26
SECTION 6.02.   Acceleration ............................................ 27
SECTION 6.03.   Other Remedies .......................................... 27
SECTION 6.04.   Waiver of Past Defaults ................................. 28
SECTION 6.05.   Control by Majority ..................................... 28
SECTION 6.06.   Limitation on Suits ..................................... 28
SECTION 6.07.   Rights of Holders to Receive Payment or Convert ......... 28
SECTION 6.08.   Collection Suit by Trustee .............................. 29
SECTION 6.09.   Trustee May File Proofs of Claim ........................ 29
SECTION 6.10.   Priorities .............................................. 29
SECTION 6.11.   Undertaking for Costs ................................... 29

                                  ARTICLE SEVEN

                                     TRUSTEE

SECTION 7.01.   Duties of Trustee ....................................... 30
SECTION 7.02.   Rights of Trustee ....................................... 31
SECTION 7.03.   Individual Rights of Trustee ............................ 32
SECTION 7.04.   Trustee's Disclaimer .................................... 32
SECTION 7.05.   Notice of Defaults ...................................... 32
SECTION 7.06.   Reports by Trustee to Holders ........................... 32
SECTION 7.07.   Compensation and Indemnity .............................. 32


                                      -ii-
<PAGE>

                                                                         Page
                                                                         ----

SECTION 7.08.   Replacement of Trustee .................................. 33
SECTION 7.09.   Successor Trustee by Merger etc. ........................ 34
SECTION 7.10.   Eligibility; Disqualification ........................... 34
SECTION 7.11.   Preferential Collection of Claims Against Company ....... 34

                                  ARTICLE EIGHT

                     SATISFACTION AND DISCHARGE; DEFEASANCE

SECTION 8.01.   Termination of Company's Obligations .................... 35
SECTION 8.02.   Application of Trust Money .............................. 36
SECTION 8.03.   Repayment to Company .................................... 36
SECTION 8.04.   Reinstatement ........................................... 36

                                  ARTICLE NINE

                                   AMENDMENTS

SECTION 9.01.   Without Consent of Holders .............................. 37
SECTION 9.02.   With Consent of Holders ................................. 37
SECTION 9.03.   Compliance with Trust Indenture Act ..................... 38
SECTION 9.04.   Revocation and Effect of Consents ....................... 38
SECTION 9.05.   Notation on or Exchange of Securities ................... 38
SECTION 9.06.   Trustee Protected ....................................... 39

                                   ARTICLE TEN

                                   CONVERSION

SECTION 10.01.  Conversion Privilege; Restrictive Legends ............... 39
SECTION 10.02.  Conversion Procedure .................................... 39
SECTION 10.03.  Fractional Shares ....................................... 40
SECTION 10.04.  Taxes on Conversion ..................................... 40
SECTION 10.05.  Company to Provide Stock ................................ 40
SECTION 10.06.  Adjustment of Conversion Price .......................... 41
SECTION 10.07.  Effect of Reclassification, Consolidation,
                Merger or Sale .......................................... 50
SECTION 10.08.  Notice of Certain Transactions .......................... 51
SECTION 10.09.  Company Determination Final ............................. 51
SECTION 10.10.  Trustee's Disclaimer .................................... 51


                                      -iii-
<PAGE>

                                                                         Page
                                                                         ----

                                 ARTICLE ELEVEN

                                   [RESERVED]

                                 ARTICLE TWELVE

                                  SUBORDINATION

SECTION 12.01.  Securities Subordinated to Senior Indebtedness .......... 52
SECTION 12.02.  Subrogation ............................................. 54
SECTION 12.03.  Obligation of Company Unconditional ..................... 54
SECTION 12.04.  Modification of Terms of Senior Indebtedness ............ 54
SECTION 12.05.  [Reserved] .............................................. 55
SECTION 12.06.  Effectuation of Subordination by Trustee ................ 55
SECTION 12.07.  Knowledge of Trustee .................................... 55
SECTION 12.08.  Trustee's Relation to Senior Indebtedness ............... 56
SECTION 12.09.  Rights of Holders of Senior Indebtedness Not Impaired ... 56
SECTION 12.10.  Certain Conversions Not Deemed Payment .................. 56

                                ARTICLE THIRTEEN

                                  MISCELLANEOUS

SECTION 13.01.  Trust Indenture Act Controls ............................ 57
SECTION 13.02.  Notices ................................................. 57
SECTION 13.03.  Communication by Holders with Other Holders ............. 58
SECTION 13.04.  Certificate and Opinion as to Conditions Precedent ...... 58
SECTION 13.05.  Statements Required in Certificate or Opinion ........... 58
SECTION 13.06.  Rules by Trustee and Agents ............................. 59
SECTION 13.07.  Legal Holidays .......................................... 59
SECTION 13.08.  No Recourse Against Others .............................. 59
SECTION 13.09.  Duplicate Originals ..................................... 59
SECTION 13.10.  Governing Law ........................................... 59
SECTION 13.11.  No Adverse Interpretation of Other Agreements ........... 59
SECTION 13.12.  Successors .............................................. 59
SECTION 13.13.  Separability ............................................ 60
SECTION 13.14.  Table of Contents, Headings, etc. ....................... 60

SIGNATURES ..............................................................S-1


                                      -iv-
<PAGE>

EXHIBITS

Exhibit A - Form of Security
Exhibit B - Form of Legends
Exhibit C - Form of Certificate to Be Delivered in Connection with Transfers to
              Non-QIB Accredited Investors
Exhibit D - Form of Certificate to Be Delivered in Connection with Transfers
              Pursuant to Regulation S
Exhibit E - Form of Notice of Transfer Pursuant to Registration Statement
Exhibit F - Form of Opinion of Counsel in Connection with Registration of
              Securities


                                       -v-
<PAGE>

            INDENTURE dated as of March 8, 2000 between ALEXION PHARMACEUTICALS,
INC., a Delaware corporation (the "Company"), and THE CHASE MANHATTAN BANK, as
trustee (the "Trustee").

            Each party agrees as follows for the benefit of the other party and
for the equal and ratable benefit of the Holders of the Company's 5 3/4%
Convertible Subordinated Notes Due 2007:

                                   ARTICLE ONE

                   DEFINITIONS AND INCORPORATION BY REFERENCE

SECTION 1.01. Definitions.

            "Affiliate" means any Person directly or indirectly controlling or
controlled by or under direct or indirect common control with the Company. For
this purpose, "control" shall mean the power to direct the management and
policies of a Person through the ownership of securities, by contract or
otherwise.

            "Agent" means any Registrar, Paying Agent, Conversion Agent or
co-registrar.

            "Board of Directors" means the Board of Directors of the Company or
any committee of the Board authorized to act for it hereunder.

            "Board Resolution" means a copy of a resolution certified by the
Secretary or an Assistant Secretary of the Company to have been duly adopted by
the Board of Directors and to be in full force and effect on the date of such
certification, and delivered to the Trustee.

            "Capital Stock" means any and all shares, interests, participations
or other equivalents (however designated) of capital stock of the Company and
all warrants or options to acquire such capital stock.

            "Common Stock" means the common stock, par value $.0001 per share,
of the Company.

            "Company" means the party named as such above until a successor
replaces it pursuant to the applicable provision hereof and thereafter means the
successor.

            "Company Request" or "Company Order" means a written request or
order signed on behalf of the Company by its Chairman of the Board, its
President or any Vice President and by its Treasurer or an Assistant Treasurer,
its Secretary or an Assistant Secretary, and delivered to the Trustee.

<PAGE>
                                      -2-


            "Conversion Price" means $106.425 per share of Common Stock, as
adjusted pursuant to Article Ten.

            "Corporate Trust Office of the Trustee" shall be at the address of
the Trustee specified in Section 13.02 or such other address as the Trustee may
give notice of to the Company.

            "Default" means any event which is, or after notice or passage of
time or both would be, an Event of Default.

            "Depository" means The Depository Trust Company, its nominees and
successors.

            "Designated Senior Indebtedness" means any Senior Indebtedness in
which the instrument creating or evidencing the same or the assumption or
guarantee thereof (or related agreements or documents to which the Company is a
party) expressly provides that such Senior Indebtedness shall be "Designated
Senior Indebtedness" for purposes of this Indenture.

            "Exchange Act" means the Securities Exchange Act of 1934, as
amended.

            "Holder" means a Person in whose name a Security is registered on
the Registrar's books.

            "IAI Global Security" means a permanent Global Security in
registered form representing the aggregate principal amount of Securities
transferred to Institutional Accredited Investors.

            "Indebtedness" means, with respect to any Person, (i) all
obligations, contingent or otherwise, of such Person (a) for borrowed money
(whether or not the recourse of the lender is to the whole of the assets of such
Person or only to a portion thereof), (b) evidenced by a note, debenture, bond
or written instrument (including a purchase money obligation), (c) in respect of
leases of such Person required, in conformity with generally accepted accounting
principles, to be accounted for as capitalized lease obligations on the balance
sheet of such Person and all obligations and other liabilities (contingent or
otherwise) under any lease or related document (including a purchase agreement)
in connection with the lease of real property which provides that such Person is
contractually obligated to purchase or cause a third party to purchase the
leased property and thereby guarantee a minimum residual value of the leased
property to the lessor and the obligations of such Person under such lease or
related document to purchase or to cause a third party to purchase such leased
property or (d) in respect of letters of credit (including reimbursement
obligations with respect thereto) or bankers' acceptances; (ii) all obligations
of others of the type described in clause (i) above or in clause (iii), (iv) or
(v) below assumed by or guaranteed in any manner by such Person or in effect
guaranteed by such Person through an agreement to purchase, contingent or
otherwise (and the obligations of such Person under any such assumptions,
guarantees or other such arrangements); (iii) all obligations secured by a
mortgage, pledge, lien, encumbrance, charge or adverse claim affecting title or
resulting in an encumbrance to which the property or assets of such Person are
subject, whether or not the obligation secured thereby shall have been assumed
by or shall otherwise be such Person's legal liability; (iv) to the extent not
otherwise included, all obligations of such Person under interest rate and
currency swap agreements, cap, floor and collar agreements, spot and forward
contracts and

<PAGE>
                                      -3-


similar agreements and arrangements; and (v) all obligations, contingent or
otherwise, of such Person under or in respect of any and all deferrals,
renewals, extensions and refundings of, or amendments, modifications or
supplements to, any liability of the kind described in any of the preceding
clauses (i), (ii), (iii) or (iv).

            "Indenture" means this Indenture as amended or supplemented from
time to time.

            "Institutional Accredited Investor" means an "accredited investor"
within the meaning of Rule 501(a)(1), (2), (3) or (7) under the Securities Act
that is an institutional investor.

            "interest" means, with respect to any Security, interest on the
Security plus liquidated damages, if any.

            "Issue Date" means (i) March 8, 2000 with respect to the
$120,000,000 aggregate principal amount of Securities issued on such date, and
(ii) with respect to any of up to $30,000,000 aggregate principal amount of
Securities that may be issued after March 8, 2000 pursuant to the option
described in Section 2.01, the respective issue date of such Securities.

            "liquidated damages" has the meaning provided in the Registration
Rights Agreement.

            "Maturity Date" means March 15, 2007.

            "Non-U.S. Person" means a Person who is not a U.S. Person, as
defined in Regulation S under the Securities Act.

            "Officer" means the Chairman of the Board, the President, any Vice
President, the Chief Financial Officer, the Treasurer or the Secretary of the
Company.

            "Officers' Certificate" means a certificate signed by two Officers
or by an Officer and an Assistant Treasurer or an Assistant Secretary of the
Company.

            "Opinion of Counsel" means a written opinion from legal counsel who
may be an employee of or counsel for the Company or other counsel reasonably
acceptable to the Trustee.

            "Person" means any individual, corporation, partnership, joint
venture, association, joint-stock company, limited liability company, trust,
unincorporated organization or government or other agency or political
subdivision thereof.

            "principal" of a debt security means the principal of the security
plus the premium, if any, on the security.

            "QIB" means a "qualified institutional buyer" within the meaning of
Rule 144A under the Securities Act.

<PAGE>
                                      -4-


            "Registration Rights Agreement" means the Registration Rights
Agreement dated as of March 8, 2000 between the Company and the Initial
Purchasers.

            "Regulation S" means Regulation S under the Securities Act.

            "Regulation S Global Security" means a permanent Global Security in
registered form representing the aggregate principal amount of Securities sold
in reliance on Regulation S.

            "Restricted Security" means a Security that constitutes a
"Restricted Security" within the meaning of Rule 144(a)(3) under the Securities
Act; provided, however, that the Trustee shall be entitled to request and
conclusively rely on an Opinion of Counsel with respect to whether any Security
constitutes a Restricted Security.

            "Rule 144A Global Security" means a permanent Global Security in
registered form representing the aggregate principal amount of Securities sold
in reliance on Rule 144A.

            "SEC" means the Securities and Exchange Commission.

            "Securities" means the 5 3/4% Convertible Subordinated Notes Due
2007 issued by the Company pursuant to this Indenture.

            "Securities Act" means the Securities Act of 1933, as amended.

            "Senior Indebtedness" means the principal of, premium, if any, and
interest on, rent payable under, and any other amounts due on or in connection
with any and all Indebtedness of the Company (including, without limitation,
fees, costs, expenses and any interest accruing after the filing of a petition
initiating any proceeding pursuant to any bankruptcy law, but only to the extent
allowed or permitted to the holder of such Indebtedness against the bankruptcy
or other insolvency estate of the Company in such proceeding), whether
outstanding on the date of this Indenture or thereafter created, incurred,
assumed, guaranteed or in effect guaranteed by the Company (including all
deferrals, renewals, extensions or refundings of, or amendments, modifications
or supplements to the foregoing); provided, however, that Senior Indebtedness
does not include (i) Indebtedness evidenced by the Securities, (ii) Indebtedness
of the Company to any subsidiary of the Company except to the extent such
Indebtedness is pledged by such subsidiary as security for any Senior
Indebtedness, (iii) accounts payable of the Company to trade creditors arising
in the ordinary course of business, and (iv) any particular Indebtedness in
which the instrument creating or evidencing the same or the assumption or
guarantee thereof expressly provides that such Indebtedness shall not be senior
in right of payment to, or is pari passu with, or is subordinated or junior to,
the Securities.

            "subsidiary" means (i) a corporation a majority of whose capital
stock with voting power, under ordinary circumstances, to elect directors is at
the time, directly or indirectly, owned by the Company, by one or more
subsidiaries of the Company or by the Company and one or more subsidiaries
thereof or (ii) any other Person (other than a corporation) in which the
Company, one or more subsidiaries thereof or the Company and one or more
subsidiaries thereof, directly or indirectly, at the date of determination
thereof, have at least majority ownership interest.

<PAGE>
                                      -5-


            "TIA" means the Trust Indenture Act of 1939 (15 U.S. Code ss.ss.
77aaa-77bbbb) as in effect on the date of this Indenture, except as provided in
Section 9.03.

            "Trust Officer" means any officer of the Trustee assigned by the
Trustee to administer this Indenture.

            "Trustee" means the party named as such in this Indenture until a
successor replaces it in accordance with the provisions hereof and thereafter
means the successor.

SECTION 1.02. Other Definitions.

              Term                                    Defined in Section
              ----                                    ------------------

        "Bankruptcy Law" ..........................       6.01
        "Business Day" ............................      13.07
        "Change in Control" .......................       3.07(1)
        "Closing Price" ...........................      10.06(h)
        "Common Dividend Amount" ..................      10.06(e)
        "Company Notice" ..........................       3.07(b)
        "Continuing Director" .....................       3.07(1)
        "Conversion Agent" ........................       2.03
        "Current Market Price" ....................      10.06(h)
        "Custodian" ...............................       6.01
        "Event of Default" ........................       6.01
        "fair market value" .......................      10.06(h)
        "Global Security" .........................       2.01
        "Initial Purchasers" ......................       2.02
        "Legal Holiday" ...........................      13.07
        "Market Capitalization" ...................      10.06(e)
        "Participants" ............................       2.15
        "Paying Agent" ............................       2.03
        "Payment Blockage Notice" .................      12.01(b)
        "Payment Blockage Period" .................      12.01(b)
        "Payment Default" .........................      12.01(b)
        "Physical Securities" .....................       2.15(b)
        "Private Placement Legend" ................       2.17
        "Record Date" .............................      10.06(h)
        "Registrar" ...............................       2.03
        "Repurchase Date" .........................       3.07(a)
        "Repurchase Event" ........................       3.07(1)
        "Repurchase Price .........................       3.07
        "Subject Securities" ......................      10.06(d)
        "Termination of Trading" ..................       3.07(1)
        "Trading Day" .............................      10.06(h)

<PAGE>
                                      -6-


        "Trigger Event" ...........................      10.06(d)
        "U.S. Government Obligations" .............       8.01

SECTION 1.03. Incorporation by Reference of Trust Indenture Act.

            Whenever this Indenture refers to a provision of the TIA, the
provision is incorporated by reference in and made a part of this Indenture.

            The following TIA terms used in this Indenture have the following
meanings:

            "Commission" means the SEC;

            "indenture securities" means the Securities;

            "indenture security holder" means a Holder;

            "indenture to be qualified" means this Indenture;

            "indenture trustee" or "institutional trustee" means the Trustee;
and

            "obligor" on the indenture securities means the Company.

            All other terms used in this Indenture that are defined by the TIA,
defined by TIA reference to another statute or defined by SEC rule under the TIA
and not otherwise defined herein have the meanings so assigned to them.

SECTION 1.04. Rules of Construction.

            Unless the context otherwise requires:

            (1) a term has the meaning assigned to it;

            (2) an accounting term not otherwise defined has the meaning
      assigned to it in accordance with generally accepted accounting principles
      in effect on the date hereof;

            (3) "or" is not exclusive;

            (4) words in the singular include the plural and in the plural
      include the singular;

            (5) provisions apply to successive events and transactions; and

            (6) "herein", "hereof" and other words of similar import refer to
      this Indenture as a whole and not to any particular Article, Section or
      other subdivision.

<PAGE>
                                      -7-


                                   ARTICLE TWO

                                 THE SECURITIES

SECTION 2.01. Form and Dating.

            The Securities and the Trustee's certificate of authentication shall
be substantially in the form set forth in Exhibit A, which is incorporated in
and forms a part of this Indenture. The Securities may have notations, legends
or endorsements required by law, stock exchange rule or usage. Each Security
shall be dated the date of its authentication.

            Securities offered and sold in reliance on Rule 144A, Securities
offered and sold in reliance on Regulation S and Securities subsequently
transferred to Institutional Accredited Investors shall be issued initially in
the form of one or more Global Securities, substantially in the form set forth
in Exhibit A (the "Global Security"). The aggregate principal amount of the
Global Security may from time to time be increased or decreased by adjustments
made on the records of the Trustee, as custodian for the Depository, as
hereinafter provided.

SECTION 2.02. Execution and Authentication.

            Two Officers shall sign the Securities for the Company by manual or
facsimile signature.

            If an Officer whose signature is on a Security no longer holds that
office at the time the Security is authenticated, the Security shall
nevertheless be valid.

            A Security shall not be valid until authenticated by the manual
signature of the Trustee. The signature shall be conclusive evidence that the
Security has been authenticated under this Indenture.

            Upon a written order of the Company signed by two Officers or by an
Officer and an Assistant Treasurer of the Company, the Trustee shall
authenticate Securities for original issue in the principal amount of
$120,000,000 and such additional principal amounts, if any, as shall be
determined pursuant to the next sentence of this Section 2.02. Upon receipt by
the Trustee of an Officers' Certificate stating that the Initial Purchasers have
elected to purchase from the Company a specified principal amount of additional
Securities, not to exceed $30,000,000, pursuant to Section 1 of the Purchase
Agreement dated as of March 3, 2000 between the Company, as issuer, and J.P.
Morgan Securities Inc., U.S. Bancorp Piper Jaffray Inc., Chase Securities Inc.
and Warburg Dillon Read LLC, as initial purchasers (the "Initial Purchasers"),
the Trustee shall authenticate and deliver such specified principal amount of
additional Securities to or upon the written order of the Company signed as
provided in the immediately preceding sentence. Such Officers' Certificate must
be received by the Trustee at least two full Business Days prior to the proposed
date for delivery of such additional Securities, but, in any case, not later
than April 5, 2000. The aggregate principal amount of Securities outstanding at
any time may not exceed $150,000,000 except as provided in Section 2.07.

<PAGE>
                                      -8-


            Upon a written order of the Company signed by two Officers or by an
Officer and an Assistant Treasurer of the Company, the Trustee shall
authenticate Securities not bearing the Private Placement Legend to be issued to
the transferee when sold pursuant to an effective registration statement under
the Securities Act.

            The Trustee may appoint an authenticating agent acceptable to the
Company to authenticate Securities. An authenticating agent may authenticate
Securities whenever the Trustee may do so. Each reference in this Indenture to
authentication by the Trustee includes authentication by such Agent. An
authenticating agent has the same rights as an Agent to deal with the Company or
an Affiliate.

            The Securities shall be issuable only in registered form without
coupons and only in denominations of $1,000 principal amount and any integral
multiple thereof.

SECTION 2.03. Registrar, Paying Agent and Conversion Agent.

            The Company shall maintain an office or agency where Securities may
be presented for registration of transfer or for exchange ("Registrar"), an
office or agency where Securities may be presented for payment ("Paying Agent")
and an office or agency where Securities may be presented for conversion
("Conversion Agent"). The Registrar shall keep a register of the Securities and
of their transfer and exchange. The Company may appoint or change one or more
co-registrars, one or more additional paying agents and one or more additional
conversion agents without notice and may act in any such capacity on its own
behalf. The term "Registrar" includes any co-registrar; the term "Paying Agent"
includes any additional paying agent; the term "Conversion Agent" includes any
additional conversion agent.

            The Company shall enter into an appropriate agency agreement with
any Agent not a party to this Indenture. The agreement shall implement the
provisions of this Indenture that relate to such Agent. The Company shall notify
the Trustee of the name and address of any Agent not a party to this Indenture.
If the Company fails to maintain a Registrar, Paying Agent or Conversion Agent,
the Trustee shall act as such.

            The Company initially appoints the Trustee as Paying Agent,
Registrar and Conversion Agent.

SECTION 2.04. Paying Agent to Hold Money in Trust.

            Each Paying Agent shall hold in trust for the benefit of the Holders
or the Trustee all moneys held by the Paying Agent for the payment of principal
of or interest on the Securities, and shall notify the Trustee of any default by
the Company in making any such payment. While any such default continues, the
Trustee may require a Paying Agent to pay all money held by it to the Trustee.
The Company at any time may require a Paying Agent to pay all money held by it
to the Trustee. Upon payment over to the Trustee, the Paying Agent shall have no
further liability for the money. If the Company acts as Paying Agent, it shall
segregate and hold as a separate trust fund all money held by it as Paying
Agent.

<PAGE>
                                      -9-


SECTION 2.05. Securityholder Lists.

            The Trustee shall preserve in as current a form as is reasonably
practicable the most recent list available to it of the names and addresses of
Holders. If the Trustee is not the Registrar, the Company shall furnish to the
Trustee on or before each interest payment date and at such other times as the
Trustee may request in writing a list, in such form and as of such date as the
Trustee may reasonably require, of the names and addresses of Holders.

SECTION 2.06. Transfer and Exchange.

            Where Securities are presented to the Registrar with a request to
register their transfer or to exchange them for an equal principal amount of
Securities of other authorized denominations, the Registrar shall register the
transfer or make the exchange if its requirements for such transaction are met.
To permit registrations of transfer and exchanges, the Company shall execute and
the Trustee shall authenticate Securities at the Registrar's request. The
Company or the Trustee, as the case may be, shall not be required (a) to issue
or authenticate, register the transfer of or exchange any Security during a
period beginning at the opening of business 15 days before the mailing of a
notice of redemption of the Securities selected for redemption under Section
3.03 and ending at the close of business on the day of such mailing, or (b) to
register the transfer of or exchange any Security so selected for redemption in
whole or in part, except the unredeemed portion of Securities being redeemed in
part.

            No service charge shall be made for any registration of transfer,
exchange or conversion of Securities, but the Company may require payment of a
sum sufficient to cover any tax or other governmental charge that may be imposed
in connection with any transfer, registration of transfer or exchange of
Securities, other than exchanges pursuant to Sections 2.10, 3.06, 9.05 or 10.02
not involving any transfer.

SECTION 2.07. Replacement Securities.

            If the Holder of a Security claims that the Security has been
mutilated, lost, destroyed or wrongfully taken, the Company shall issue and the
Trustee shall authenticate a replacement Security if the Trustee's requirements
are met and, in the case of a mutilated Security, such mutilated Security is
surrendered to the Trustee. In the case of lost, destroyed or wrongfully taken
Securities, if required by the Trustee or the Company, an indemnity bond must be
provided by the Holder that is sufficient in the judgment of both to protect the
Company, the Trustee or any Agent from any loss which any of them may suffer if
a Security is replaced. The Company or the Trustee may charge for its expenses
in replacing a Security.

            In case any such mutilated, lost, destroyed or wrongfully taken
Security has become or is about to become due and payable, the Company in its
discretion may, instead of issuing a new Security, pay such Security when due.

            Every replacement Security is an additional obligation of the
Company.

<PAGE>
                                      -10-


SECTION 2.08. Outstanding Securities.

            Securities outstanding at any time are all the Securities
authenticated by the Trustee except for those converted, those cancelled by it,
those delivered to it for cancellation and those described in this Section as
not outstanding. A Security does not cease to be outstanding because the Company
or one of its subsidiaries or Affiliates holds the Security.

            If a Security is replaced pursuant to Section 2.07, it ceases to be
outstanding unless the Trustee receives proof satisfactory to it, or a court
holds, that the replaced Security is held by a protected purchaser.

            If the Paying Agent (other than the Company) holds on a redemption
date or maturity date money sufficient to pay Securities payable on that date,
then on and after that date, such Securities shall be deemed to be no longer
outstanding and interest on them shall cease to accrue.

SECTION 2.09. Securities Held by the Company or an Affiliate.

            In determining whether the Holders of the required aggregate
principal amount of Securities have concurred in any direction, waiver or
consent, Securities owned by the Company or a subsidiary or an Affiliate shall
be disregarded, except that for the purposes of determining whether the Trustee
shall be protected in relying on any such direction, waiver or consent, only
Securities which a Trust Officer knows are so owned shall be so disregarded.

SECTION 2.10. Temporary Securities.

            Until definitive Securities are ready for delivery, the Company may
prepare and the Trustee shall authenticate temporary Securities. Temporary
Securities shall be substantially in the form of definitive Securities but may
have variations that the Company considers appropriate for temporary Securities.
Without unreasonable delay, the Company shall prepare and the Trustee shall
authenticate definitive Securities in exchange for temporary Securities.

SECTION 2.11. Cancellation.

            The Company at any time may deliver Securities to the Trustee for
cancellation. The Registrar, Paying Agent and Conversion Agent shall forward to
the Trustee any Securities surrendered to them for registration of transfer,
exchange, payment or conversion. The Trustee shall cancel all Securities
surrendered for registration of transfer, exchange, payment, conversion or
cancellation and the Trustee may, but shall not be required to, destroy
cancelled Securities and deliver a certificate of any such destruction to the
Company or return such cancelled Securities to the Company. The Company may not
issue new Securities to replace Securities that it has paid or delivered to the
Trustee for cancellation or that any Holder has converted pursuant to Article
Ten.

<PAGE>
                                      -11-


SECTION 2.12. Defaulted Interest.

            If and to the extent the Company defaults in a payment of interest
on the Securities, it shall pay the defaulted interest in any lawful manner
plus, to the extent not prohibited by applicable statute or case law, interest
payable on the defaulted interest. It may pay the defaulted interest to the
Persons who are Holders on a subsequent special record date. The Company shall
fix such record date and payment date. At least 15 days before the record date,
the Company shall mail to Holders a notice that states the record date, payment
date and amount of interest to be paid.

SECTION 2.13. CUSIP Numbers.

            The Company in issuing the Securities may use one or more "CUSIP"
numbers, and if so, the Trustee shall use the CUSIP numbers in notices of
redemption or exchange as a convenience to Holders; provided, however, that no
representation is hereby deemed to be made by the Trustee as to the correctness
or accuracy of the CUSIP numbers printed in the notice or on the Securities, and
that reliance may be placed only on the other identification numbers printed on
the Securities. The Company shall promptly notify the Trustee of any change in
the CUSIP number.

SECTION 2.14. Deposit of Moneys.

            Prior to 11:00 a.m., New York City time, on each interest payment
date, maturity date, redemption date and Repurchase Date, the Company shall have
deposited with the Paying Agent in immediately available funds money sufficient
to make cash payments, if any, due on such interest payment date, maturity date,
redemption date and Repurchase Date, as the case may be, in a timely manner
which permits the Paying Agent to remit payment to the Holders on such interest
payment date, maturity date, redemption date and Repurchase Date, as the case
may be.

SECTION 2.15. Book-Entry Provisions for Global Securities.

            (a) The Global Securities initially shall (i) be registered in the
name of the Depository or the nominee of such Depository, (ii) be delivered to
the Trustee as custodian for such Depository and (iii) bear the legend for
Global Securities as set forth in Exhibit B(II).

            Members of, or participants in, the Depository ("Participants")
shall have no rights under this Indenture with respect to any Global Security
held on their behalf by the Depository, or the Trustee as its custodian, or
under the Global Security, and the Depository may be treated by the Company, the
Trustee and any agent of the Company or the Trustee as the absolute owner of the
Global Security for all purposes whatsoever. Notwithstanding the foregoing,
nothing herein shall prevent the Company, the Trustee or any agent of the
Company or the Trustee from giving effect to any written certification, proxy or
other authorization furnished by the Depository or impair, as between the
Depository and Participants, the operation of customary practices governing the
exercise of the rights of a Holder of any Security.

            (b) Transfers of Global Securities shall be limited to transfers in
whole, but not in part, to the Depository, its successors or their respective
nominees. In addition, permanent certifi-

<PAGE>
                                      -12-


cated Securities in registered form, in the form set forth in Exhibit A (the
"Physical Securities"), shall be transferred to all beneficial owners in
exchange for their beneficial interests in Global Securities if (i) the
Depository notifies the Company that it is unwilling or unable to continue as
Depository for any Global Security and a successor Depository is not appointed
by the Company within 90 days of such notice or (ii) an Event of Default has
occurred and is continuing and the Registrar has received a written request from
the Depository to issue Physical Securities.

            (c) In connection with any transfer or exchange of a portion of the
beneficial interest in a Global Security to beneficial owners pursuant to
paragraph (b), the Registrar shall (if one or more Physical Securities are to be
issued) reflect on its books and records the date and a decrease in the
aggregate principal amount of such Global Security in an amount equal to the
aggregate initial aggregate principal amount of the beneficial interest in the
Global Security to be transferred, and the Company shall execute and the Trustee
shall authenticate and deliver one or more Physical Securities of authorized
denominations in an aggregate principal amount equal to the aggregate principal
amount of the beneficial interest in the Global Security so transferred.

            (d) In connection with the transfer of a Global Security in its
entirety to beneficial owners pursuant to paragraph (b) of this Section 2.15,
such Global Security shall be deemed to be surrendered to the Trustee for
cancellation, and the Company shall execute, and the Trustee shall upon written
instructions from the Company authenticate and deliver, to each beneficial owner
identified by the Depository in exchange for its beneficial interest in such
Global Security, an equal aggregate principal amount of Physical Securities of
authorized denominations.

            (e) Any Physical Security constituting a Restricted Security
delivered in exchange for an interest in a Global Security pursuant to paragraph
(b) or (c) of this Section 2.15 shall, except as otherwise provided by Section
2.16, bear the Private Placement Legend.

            (f) The Holder of any Global Security may grant proxies and
otherwise authorize any Person, including Participants and Persons that may hold
interests through Participants, to take any action which a Holder is entitled to
take under this Indenture or the Securities.

SECTION 2.16. Special Transfer Provisions.

            (a)Transfers to Non-QIB Institutional Accredited Investors and
Non-U.S. Persons. The following provisions shall apply with respect to the
registration of any proposed transfer of a Restricted Security to any
Institutional Accredited Investor which is not a QIB or to any Non-U.S. Person:

            (i) the Registrar shall register the transfer of any Restricted
      Security, whether or not such Security bears the Private Placement Legend,
      if (x) the requested transfer is after the second anniversary of the Issue
      Date for such Security; provided, however, that the transferor shall
      represent to the Registrar that, to the transferor's knowledge, neither
      the Company nor any Affiliate of the Company has held any beneficial
      interest in such Security, or portion thereof, at any time on or prior to
      the second anniversary of the Issue Date for such Security or (y)(1) in
      the case of a transfer to an Institutional Accredited Investor which is
      not a QIB

<PAGE>
                                      -13-


      (excluding Non-U.S. Persons), the proposed transferee has delivered to the
      Registrar a certificate substantially in the form of Exhibit C hereto and
      any legal opinions and certifications required thereby and (2) in the case
      of a transfer to a Non-U.S. Person, the proposed transferee has delivered
      to the Registrar a certificate substantially in the form of Exhibit D
      hereto;

            (ii) if the proposed transferee is a Participant and the Securities
      to be transferred consist of Physical Securities which after transfer are
      to be evidenced by an interest in the Global Security, upon receipt by the
      Registrar of (x) written instructions given in accordance with the
      Depository's and the Registrar's procedures and (y) the appropriate
      certificate, if any, required by clause (y) of paragraph (i) above, the
      Registrar shall register the transfer and reflect on its books and records
      the date and an increase in the aggregate principal amount of the Global
      Security in an amount equal to the aggregate principal amount of Physical
      Securities to be transferred, and the Trustee shall cancel the Physical
      Securities so transferred; and

            (iii) if the proposed transferor is a Participant seeking to
      transfer an interest in the Rule 144A Global Security, upon receipt by the
      Registrar of (x) written instructions given in accordance with the
      Depository's and the Registrar's procedures and (y) the appropriate
      certificate, if any, required by clause (y) of paragraph (i) above, the
      Registrar shall register the transfer and reflect on its books and records
      the date and (A) a decrease in the aggregate principal amount of the Rule
      144A Global Security in an amount equal to the aggregate principal amount
      of the Securities to be transferred and (B) an increase in the aggregate
      principal amount of the Regulation S Global Security or the IAI Global
      Security, as the case may be, in an amount equal to the aggregate
      principal amount of the Securities to be transferred.

            (b) Transfers to QIBs. The following provisions shall apply with
respect to the registration of any proposed transfer of a Restricted Security to
a QIB:

            (i) the Registrar shall register the transfer of any Restricted
      Security, whether or not such Security bears the Private Placement Legend,
      if (x) the requested transfer is after the second anniversary of the Issue
      Date for such Security; provided, however, that the transferor shall
      represent to the Registrar that, to the transferor's knowledge, neither
      the Company nor any Affiliate of the Company has held any beneficial
      interest in such Security, or portion thereof, at any time on or prior to
      the second anniversary of the Issue Date for such Security or (y) such
      transfer is being made by a proposed transferor who has checked the box
      provided for on the form of Security stating, or has otherwise advised the
      Company and the Registrar in writing, that the sale has been made in
      compliance with the provisions of Rule 144A to a transferee who has signed
      the certification provided for on the form of Security stating, or has
      otherwise advised the Company and the Registrar in writing, that it is
      purchasing the Security for its own account or an account with respect to
      which it exercises sole investment discretion and that it and any such
      account is a QIB within the meaning of Rule 144A, and is aware that the
      sale to it is being made in reliance on Rule 144A and acknowledges that it
      has received such information regarding the Company as it has requested
      pursuant to Rule 144A or has determined not to request such information
      and that it is aware that the transferor is relying

<PAGE>
                                      -14-


      upon its foregoing representations in order to claim the exemption from
      registration provided by Rule 144A;

            (ii) if the proposed transferee is a Participant and the Securities
      to be transferred consist of Physical Securities which after transfer are
      to be evidenced by an interest in the Global Security, upon receipt by the
      Registrar of written instructions given in accordance with the
      Depository's and Registrar's procedures, the Registrar shall register the
      transfer and reflect on its books and records the date and an increase in
      the principal amount of the Global Security in an amount equal to the
      principal amount of Physical Securities to be transferred, and the Trustee
      shall cancel the Physical Security so transferred; and

            (iii) if the proposed transferor is a Participant seeking to
      transfer an interest in the Regulation S Global Security or the IAI Global
      Security, upon receipt by the Registrar of written instructions given in
      accordance with the Depository's and the Registrar's procedures, the
      Registrar shall register the transfer and reflect on its books and records
      the date and (A) a decrease in the aggregate principal amount of the
      Regulation S Global Security or the IAI Global Security, as the case may
      be, in an amount equal to the aggregate principal amount of the Securities
      to be transferred and (B) an increase in the aggregate principal amount of
      the Rule 144A Global Security in an amount equal to the aggregate
      principal amount of the Securities to be transferred.

            (c) Restrictions on Transfer and Exchange of Global Securities.
Notwithstanding any other provisions of this Indenture, a Global Security may
not be transferred as a whole except by the Depository to a nominee of the
Depository or by a nominee of the Depository to the Depository or another
nominee of the Depository or by the Depository or any such nominee to a
successor Depository or a nominee of such successor Depository.

            (d) Private Placement Legend. Upon the registration of transfer,
exchange or replacement of Securities not bearing the Private Placement Legend,
the Registrar or co-Registrar shall deliver Securities that do not bear the
Private Placement Legend. Upon the registration of transfer, exchange or
replacement of Securities bearing the Private Placement Legend, the Registrar or
co-Registrar shall deliver only Securities that bear the Private Placement
Legend unless (i) the requested transfer is after the second anniversary of the
Issue Date for such Security (provided, however, that neither the Company nor
any Affiliate of the Company has held any beneficial interest in such Security,
or portion thereof, at any time prior to or on the second anniversary of the
Issue Date for such Security), (ii) there is delivered to the Trustee an Opinion
of Counsel reasonably satisfactory to the Company to the effect that neither
such legend nor the related restrictions on transfer are required in order to
maintain compliance with the provisions of the Securities Act or (iii) such
Security has been sold pursuant to an effective registration statement under the
Securities Act and the Holder selling such Securities has delivered to the
Registrar or co-Registrar a notice in the form of Exhibit E hereto. Upon the
effectiveness of the Shelf Registration Statement (as defined in the
Registration Rights Agreement) the Company shall deliver to the Trustee a notice
of effectiveness, a Security or Securities, an authentication order in
accordance with Section 2.02 and an Opinion of Counsel in the form

<PAGE>
                                      -15-


of Exhibit F hereto and, if required by the Depository, the Company shall
deliver to the Depository a letter of representations in a form reasonably
acceptable to the Depository.

            (e) General. By its acceptance of any Security bearing the Private
Placement Legend, each Holder of such a Security acknowledges the restrictions
on transfer of such Security set forth in this Indenture and in the Private
Placement Legend and agrees that it will transfer such Security only as provided
in this Indenture.

            The Registrar shall retain, in accordance with its customary
procedures, copies of all letters, notices and other written communications
received pursuant to Section 2.15 or this Section 2.16. The Company shall have
the right to inspect and make copies of all such letters, notices or other
written communications at any reasonable time upon the giving of reasonable
notice to the Registrar.

            (f) Transfers of Securities Held by Affiliates. Any certificate (i)
evidencing a Security that has been transferred to an Affiliate of the Company
within two years after the Issue Date for such Security, as evidenced by a
notation on the Assignment Form for such transfer or in the representation
letter delivered in respect thereof or (ii) evidencing a Security that has been
acquired from an Affiliate (other than by an Affiliate) in a transaction or a
chain of transactions not involving any public offering, shall, until two years
after the last date on which either the Company or any Affiliate of the Company
was an owner of such Security, in each case, bear the Private Placement Legend,
unless otherwise agreed by the Company (with written notice thereof to the
Trustee).

SECTION 2.17. Restrictive Legends.

            Each Global Security and Physical Security that constitutes a
Restricted Security shall bear the private placement legend (the "Private
Placement Legend") as set forth in Exhibit B(I) on the face thereof until after
the second anniversary of the later of the Issue Date for such Securities and
the last date on which the Company or any Affiliate of the Company was the owner
of such Security (or any predecessor security) (or such shorter period of time
as permitted by Rule 144(k) under the Securities Act or any successor provision
thereunder) (or such longer period of time as may be required under the
Securities Act or applicable state securities laws in the opinion of counsel for
the Company, unless otherwise agreed by the Company and the Holder thereof).

                                  ARTICLE THREE

                             REDEMPTION; REPURCHASE

SECTION 3.01. Notices to Trustee.

            If the Company wants to redeem Securities pursuant to paragraph 6 of
the Securities, it shall notify the Trustee at least 45 days prior to the
redemption date (unless a shorter notice period shall be satisfactory to the
Trustee) of the redemption date and the aggregate principal amount of Securities
to be redeemed. If the Company wants to credit against any such redemption
Securities it has

<PAGE>
                                      -16-


not previously delivered to the Trustee for cancellation (other than Securities
repurchased pursuant to Section 3.07), it shall deliver the Securities with the
notice.

SECTION 3.02. Selection of Securities to Be Redeemed.

            If less than all the Securities are to be redeemed, the Trustee
shall select the Securities to be redeemed on either a pro rata basis or by lot
or such other method as the Trustee shall deem fair and equitable. The Trustee
shall make the selection from Securities outstanding not previously called for
redemption. The Trustee may select for redemption portions of the principal of
Securities that have denominations larger than $1,000 principal amount.
Securities and portions of them it selects shall be in amounts of $1,000
principal amount or whole multiples of $1,000 principal amount. Provisions of
this Indenture that apply to Securities called for redemption also apply to
portions of Securities called for redemption.

            The Registrar need not register the transfer of or exchange any
Securities selected for redemption. Also, the Registrar need not transfer or
exchange any Securities for a period of 15 days before selecting Securities to
be redeemed.

SECTION 3.03. Notice of Redemption.

            At least 30 days but not more than 60 days before a redemption date,
the Company shall mail by first-class mail or cause to be mailed a notice of
redemption to each Holder whose Securities are to be redeemed.

            The notice shall identify the Securities and the aggregate principal
amount thereof to be redeemed and shall state:

            (1) the redemption date;

            (2) the redemption price, plus the amount of accrued and unpaid
      interest to be paid on the Securities called for redemption;

            (3) the then current conversion rate;

            (4) the name and address of the Paying Agent and Conversion Agent;

            (5) the date on which the right to convert the principal of the
      Securities called for redemption will terminate and the place or places
      where such Securities may be surrendered for conversion;

            (6) that Holders who want to convert Securities must satisfy the
      requirements in Article Ten;

            (7) that Securities called for redemption must be surrendered to the
      Paying Agent to collect the redemption price;

<PAGE>
                                      -17-


            (8) that interest on Securities called for redemption ceases to
      accrue on and after the redemption date; and

            (9) the CUSIP number of the Securities.

            The date on which the right to convert the principal of the
Securities called for redemption will terminate shall be at the close of
business on the date prior to the redemption date, or, if the day before the
redemption date is a Legal Holiday, the close of business on the next preceding
day which is not a Legal Holiday.

            At the Company's request (which request shall be furnished to the
Trustee at least 40 days prior to the redemption date (unless a shorter period
shall be acceptable to the Trustee)), the Trustee shall give the notice of
redemption in the Company's name and at the Company's expense; provided that the
form and content of such notice shall be prepared by the Company.

SECTION 3.04. Effect of Notice of Redemption.

            Once notice of redemption is mailed, Securities called for
redemption become due and payable on the redemption date at the redemption price
plus accrued and unpaid interest to the date of redemption, and, on and after
such date (unless the Company shall default in the payment of the redemption
price), such Securities shall cease to bear interest. Upon surrender to the
Paying Agent, such Securities shall be paid at the redemption price plus accrued
interest to the redemption date, unless the redemption date is an interest
payment date, in which case the accrued interest will be paid in the ordinary
course.

SECTION 3.05. Deposit of Redemption Price.

            On or before the redemption date, the Company shall deposit with the
Paying Agent pursuant to Section 2.14 money in funds immediately available on
the redemption date sufficient to pay the redemption price of and accrued
interest on all Securities to be redeemed on that date. The Paying Agent shall
return to the Company, as soon as practicable, any money not required for that
purpose because of conversion of Securities.

SECTION 3.06. Securities Redeemed in Part.

            Upon surrender of a Security that is redeemed in part, the Company
shall execute and the Trustee shall authenticate for the Holder a new Security
equal in principal amount to the unredeemed portion of the Security surrendered.

            If a portion of a Holder's Securities is selected for partial
redemption and that Holder converts a portion of that Holder's Securities, the
converted portion shall be deemed (as far as may be) to be the portion selected
for redemption.

<PAGE>
                                      -18-


SECTION 3.07. Repurchase at Option of Holder upon a Repurchase Event.

            (a) If there shall occur a Repurchase Event, then each Holder shall
have the right, at such Holder's option, to require the Company to repurchase
all of such Holder's Securities, or any portion thereof (in principal amounts of
$1,000 or integral multiples thereof), on the date (the "Repurchase Date") that
is forty (40) calendar days after the date of the Company Notice (as defined
below) of such Repurchase Event (or, if such 40th day is not a Business Day, the
next succeeding Business Day). Such repurchase shall be made in cash at a price
equal to 105% of the principal amount of Securities such Holder elects to
require the Company to repurchase, together with accrued interest, if any, to
but excluding the Repurchase Date (the "Repurchase Price") (or, at the option of
the Company, by delivery of Common Stock in accordance with the provisions of
Section 3.07(k)); provided, however, that if such Repurchase Date is March 15 or
September 15, then the interest payable on such date shall be paid to the holder
of record of the Security on the next preceding March 1 or September 1,
respectively. No Securities may be repurchased at the option of Holders upon a
Repurchase Event if there has occurred and is continuing an Event of Default,
other than a default in the payment of the Repurchase Price with respect to such
Securities on the Repurchase Date.

            (b) Unless the Company shall have theretofore called for redemption
all of the outstanding Securities, on or before the fifteenth (15th) calendar
day after the occurrence of a Repurchase Event, the Company or, at the written
request of the Company, the Trustee shall mail to all holders of record of the
Securities a notice (the "Company Notice") in the form prepared by the Company
of the occurrence of the Repurchase Event and of the repurchase right set forth
herein arising as a result thereof. The Company shall also deliver a copy of
such Company Notice to the Trustee and cause a copy of such Company Notice, or a
summary of the information contained therein, to be published once in a
newspaper of general circulation in The City of New York. The Company Notice
shall contain the following information:

            (1) the Repurchase Date;

            (2) the date by which the repurchase right must be exercised;

            (3) the last date by which the election to require repurchase, if
      submitted, must be revoked;

            (4) the Repurchase Price and whether the Repurchase Price shall be
      payable in cash or Common Stock and, if payable in Common Stock, the
      method of calculating the amount of the Common Stock to be delivered upon
      the repurchase as provided in Section 3.07(k);

            (5) a description of the procedure which a Holder must follow to
      exercise a repurchase right;
<PAGE>
                                      -19-


            (6) the Conversion Price then in effect, the date on which the right
      to convert the principal amount of the Securities to be repurchased will
      terminate and the place or places where Securities may be surrendered for
      conversion; and

            (7) the CUSIP numbers of the Securities.

            No failure of the Company to give the foregoing notices or defect
therein shall limit any Holder's right to exercise a repurchase right or affect
the validity of the proceedings for the repurchase of Securities.

            If any of the foregoing provisions are inconsistent with applicable
law, such law shall govern.

            (c) To exercise a repurchase right, a Holder shall deliver to the
Trustee on or before the thirty-fifth (35th) day after the Company Notice was
delivered (i) written notice to the Company (or agent designated by the Company
for such purpose) of the Holder's exercise of such right, which notice shall set
forth the name of the Holder, the principal amount of the Securities to be
repurchased, a statement that an election to exercise the repurchase right is
being made thereby, and, in the event that the Repurchase Price shall be paid in
shares of Common Stock, the name or names (with addresses) in which the
certificate or certificates for shares of Common Stock shall be issued, and (ii)
the Securities with respect to which the repurchase right is being exercised,
duly endorsed for transfer to the Company. Election of repurchase by a Holder
shall be revocable at any time prior to, but excluding, the Repurchase Date, by
delivering written notice to that effect to the Trustee prior to the close of
business on the Business Day prior to the Repurchase Date.

            (d) If the Company fails to repurchase on the Repurchase Date any
Securities (or portions thereof) as to which the repurchase right has been
properly exercised, then the principal of such Securities shall, until paid,
bear interest to the extent permitted by applicable law from the Repurchase Date
at the rate borne by the Securities and each such Security shall be convertible
into Common Stock in accordance with this Indenture until the principal of such
Security shall have been paid or duly provided for.

            (e) Any Security which is to be repurchased only in part shall be
surrendered to the Trustee duly endorsed for transfer to the Company and
accompanied by appropriate evidence of genuineness and authority satisfactory to
the Company and the Trustee duly executed by the Holder thereof (or his attorney
duly authorized in writing), and the Company shall execute, and the Trustee
shall authenticate and deliver to the Holder of such Security without service
charge, a new Security or Securities, containing identical terms and conditions,
of any authorized denomination as requested by such Holder in aggregate
principal amount equal to and in exchange for the unrepurchased portion of the
principal of the Security so surrendered.

            (f) On or prior to the Repurchase Date, the Company shall deposit
with the Trustee or with a Paying Agent, pursuant to Section 2.14, the
Repurchase Price in cash for payment to the Holder on the Repurchase Date;
provided that if payment is to be made in cash and such cash payment is made on
the Repurchase Date it must be received by the Trustee or paying agent, as the
case
<PAGE>
                                      -20-


may be, by 10:00 a.m., New York City time, on such date; provided, further, that
if the Repurchase Price is to be paid in shares of Common Stock, such shares of
Common Stock are to be paid as promptly after the Repurchase Date as
practicable.

            (g) Any issuance of shares of Common Stock in respect of the
Repurchase Price shall be deemed to have been effected immediately prior to the
close of business on the Repurchase Date and the Person or Persons in whose name
or names any certificate or certificates for shares of Common Stock shall be
issuable upon such repurchase shall be deemed to have become on the Repurchase
Date the holder or holders of record of the shares represented thereby;
provided, however, that any surrender for repurchase on a date when the stock
transfer books of the Company shall be closed shall constitute the Person or
Persons in whose name or names the certificate or certificates for such shares
are to be issued as the record holder or holders thereof for all purposes at the
opening of business on the next succeeding day on which such stock transfer
books are open. No payment or adjustment shall be made for dividends or
distributions on any Common Stock issued upon repurchase of any Security
declared prior to the Repurchase Date.

            (h) No fractions of shares shall be issued upon repurchase of
Securities. If more than one Security shall be repurchased from the same Holder
and the Repurchase Price shall be payable in shares of Common Stock, the number
of full shares which shall be issuable upon such repurchase shall be computed on
the basis of the aggregate principal amount of the Securities so repurchased.
Instead of any fractional share of Common Stock otherwise issuable on the
repurchase of any Security or Securities, the Company will deliver to the
applicable Holder its check for the current market value of such fractional
share. The current market value of a fraction of a share is determined by
multiplying the current market price of a full share by the fraction, and
rounding the result to the nearest cent. For purposes of this Section, the
current market price of a share of Common Stock is the Closing Price of the
Common Stock on the Trading Day immediately preceding the Repurchase Date.

            (i) Any issuance and delivery of certificates for shares of Common
Stock on repurchase of Securities shall be made without charge to the Holder of
Securities being repurchased for such certificates or for any tax or duty in
respect of the issuance or delivery of such certificates or the securities
represented thereby; provided, however, that the Company shall not be required
to pay any tax or duty which may be payable in respect of (i) income of the
Holder or (ii) any transfer involved in the issuance or delivery of certificates
for shares of Common Stock in a name other than that of the Holder of the
Securities being repurchased, and no such issuance or delivery shall be made
unless and until the Person requesting such issuance or delivery has paid to the
Company the amount of any such tax or duty or has established, to the
satisfaction of the Company, that such tax or duty has been paid.

            (j) All Securities delivered for repurchase shall be delivered to
the Trustee to be canceled in accordance with the provisions of Section 2.11.

            (k) The Company may elect to pay the Repurchase Price by delivery of
shares of Common Stock if and only if the following conditions shall have been
satisfied:
<PAGE>
                                      -21-


            (i) the shares of Common Stock deliverable in payment of the
      Repurchase Price shall have a fair market value as of the Repurchase Date
      of not less than the Repurchase Price. For purposes of this Section 3.07,
      the fair market value of shares of Common Stock shall be determined by the
      Company and shall be equal to 95% of the average of the Closing Prices of
      the Common Stock for the five consecutive Trading Days immediately
      preceding and including the third Trading Day prior to the Repurchase
      Date;

            (ii) such shares have been registered under the Securities Act or
      are freely transferable without such registration;

            (iii) the issuance of such Common Stock does not require
      registration with or approval of any governmental authority under any
      state law or any other federal law, which registration or approval has not
      been made or obtained;

            (iv) such shares have been approved for quotation on the Nasdaq
      National Market or listing on a national securities exchange; and

            (v) such shares will be issued out of the Company's authorized but
      unissued stock and, upon issuance, will be duly and validly and fully paid
      and non-assessable and free of any preemptive rights.

            (l) For purposes of this Section 3.07:

            (i) the term "beneficial owner" shall be determined in accordance
      with Rule 13d-3 and 13d-5, as in effect on the date of the original
      execution of this Indenture, promulgated by the SEC pursuant to the
      Exchange Act;

            (ii) the term "Person" or "group" shall include any syndicate or
      group which would be deemed to be a "person" under Section 13(d) and 14(d)
      of the Exchange Act as in effect on the date of this Indenture;

            (iii) the term "Continuing Director" means at any date a member of
      the Company's Board of Directors (i) who was a member of such board on
      March 3, 2000 or (ii) who was nominated or elected by at least a majority
      of the directors who were Continuing Directors at the time of such
      nomination or election or whose election to the Company's Board of
      Directors was recommended or endorsed by at least a majority of the
      directors who were Continuing Directors at the time of such nomination or
      election or such lesser number comprising a majority of a nominating
      committee if authority for such nominations or elections has been
      delegated to a nominating committee whose authority and composition have
      been approved by at least a majority of the Continuing Directors; and

            (iv) the term "Repurchase Event" means a Change in Control or a
      Termination of Trading, in each case defined as follows:
<PAGE>
                                      -22-


                  A "Change in Control" shall be deemed to have occurred when
            (i) any "person" or "group" (as such terms are used in Sections
            13(d) and 14(d) of the Exchange Act) is or becomes the "beneficial
            owner" (as defined in Rules 13-d3 and 13-d5 under the Exchange Act)
            of shares representing more than 50% of the combined voting power of
            the then outstanding securities entitled to vote generally in
            elections of directors of the Company (the "Voting Stock"); (ii) the
            stockholders of the Company approve any plan or proposal for the
            liquidation, dissolution or winding up of the Company; (iii) the
            Company (A) consolidates with or merges into any other Person or any
            other Person merges into the Company, and in the case of any such
            transaction, the outstanding Common Stock of the Company is changed
            or exchanged into other assets or securities as a result, unless the
            stockholders of the Company immediately before such transaction own,
            directly or indirectly immediately following such transaction, more
            than 50% of the combined voting power of the outstanding voting
            securities of the Person resulting from such transaction in
            substantially the same proportion as their ownership of the Voting
            Stock immediately before such transaction, or (B) conveys, transfers
            or leases all or substantially all of its assets to any Person other
            than a subsidiary or subsidiaries; or (iv) Continuing Directors do
            not at any time constitute a majority of the Board of Directors of
            the Company; provided that a Change in Control shall not be deemed
            to have occurred if either (x) the Closing Price of the Common Stock
            for any five (5) Trading Days during the ten (10) Trading Days
            immediately preceding the Change in Control is at least equal to
            105% of the Conversion Price in effect on the date on which the
            Change in Control occurs or (y) in the case of a merger or
            consolidation otherwise constituting a Change in Control, all of the
            consideration (excluding cash payments for fractional shares) in
            such merger or consolidation constituting the Change in Control
            consists of common stock traded on a United States national
            securities exchange or quoted on the Nasdaq National Market (or
            which will be so traded or quoted when issued or exchanged in
            connection with such Change in Control) and as a result of such
            transaction or transactions the Securities become convertible solely
            into such Common Stock.

                  A "Termination of Trading" shall have occurred if the Common
            Stock (or other common stock into which the Securities are then
            convertible) is neither listed for trading on a United States
            national securities exchange nor approved for trading on an
            established automated over-the-counter trading market in the United
            States.
<PAGE>
                                      -23-


                                  ARTICLE FOUR

                                    COVENANTS

SECTION 4.01. Payment of Securities.

            The Company shall pay the principal amount, premium, if any, of and
any accrued and unpaid interest on the Securities on the dates and in the manner
provided in the Securities. The principal, premium, if any, and any accrued and
unpaid interest thereon shall be considered paid on the date due if the Paying
Agent holds (or, if the Company is acting as Paying Agent, if the Company has
segregated and holds in trust in accordance with Section 2.04) on that date
money sufficient to pay the principal, premium, if any, and any accrued and
unpaid interest thereon.

            The Company shall pay interest on any overdue principal at the rate
borne by the Securities. The Company shall pay interest on overdue installments
of interest at the same rate to the extent not prohibited by applicable law.

SECTION 4.02. Maintenance of Office or Agency.

            The Company will maintain in the Borough of Manhattan, The City of
New York, an office or agency where Securities may be surrendered for
registration of transfer or exchange or conversion and where notices and demands
to or upon the Company in respect of the Securities and this Indenture may be
served. The Company will give prompt written notice to the Trustee of the
location, and any change in the location, of such office or agency. If at any
time the Company shall fail to maintain any such required office or agency or
shall fail to furnish the Trustee with the address thereof, such presentations,
surrenders, notices and demands may be made or served at the Corporate Trust
Office of the Trustee.

            The Company may also from time to time designate one or more other
offices or agencies where the Securities may be presented or surrendered for any
or all such purposes and may from time to time rescind such designations;
provided, however, that no such designation or rescission shall in any manner
relieve the Company of its obligation to maintain an office or agency in the
Borough of Manhattan, The City of New York for such purposes. The Company will
give prompt written notice to the Trustee of any such designation or rescission
and of any change in the location of any such other office or agency.

            The Company hereby designates the Corporate Trust Office of the
Trustee as an agency of the Company in accordance with Section 2.03.

            The Company also shall comply with the provisions of TIA ss. 314(a).
<PAGE>
                                      -24-


SECTION 4.03. Reports to Holders.

            (a) The Company (at its own expense) will deliver to the Trustee
within 15 days after the filing of the same with the SEC, copies of the
quarterly and annual reports and of the information, documents and other
reports, if any, the Company is required to file with the SEC pursuant to
Section 13 or 15(d) of the Exchange Act.

            (b) Notwithstanding that the Company may not be subject to the
reporting requirements of Section 13 or 15(d) of the Exchange Act, the Company
will promptly provide the information required by Rule 144A(d)(4) to any Holder
that so requests.

            (c) In addition, if and when this Indenture becomes subject to the
TIA, the Company will file a copy of all such information with the SEC for
public availability (unless the Commission will not accept such a filing) and
make such information available to investors who request it in writing. The
Company will also comply with the other provisions of TIA ss. 314(a).

SECTION 4.04. Compliance Certificate.

            The Company shall deliver to the Trustee within 120 days after the
end of each fiscal year of the Company an Officers' Certificate stating whether
or not the signers know of any Default or Event of Default by the Company in
performing any of its obligations under this Indenture or the Securities. If
they do know of any such Default or Event of Default, the certificate shall
describe the Default or Event of Default and its status.

SECTION 4.05. Stay, Extension and Usury Laws.

            The Company covenants (to the extent that it may lawfully do so)
that it will not at any time insist upon, plead, or in any manner whatsoever
claim or take the benefit or advantage of, any stay, extension or usury law
wherever enacted, now or at any time hereafter in force, which may affect the
covenants or the performance of this Indenture; and the Company (to the extent
that it may lawfully do so) hereby expressly waives all benefit or advantage of
any such law, and covenants that it will not, by resort to any such law, hinder,
delay or impede the execution of any power herein granted to the Trustee, but
will suffer and permit the execution of every such power as though no such law
has been enacted.

SECTION 4.06. Corporate Existence.

            Subject to Article Five, the Company will do or cause to be done all
things necessary to preserve and keep in full force and effect its corporate
existence and the corporate existence of each subsidiary in accordance with the
respective organizational documents of each subsidiary and the rights (charter
and statutory), licenses and franchises of the Company and its subsidiaries;
provided, however, that the Company shall not be required to preserve any such
right, license or franchise, or the corporate existence of any subsidiary, if in
the judgment of the Company, (i) such preservation or existence is not material
to the conduct of business of the Company and (ii) the loss of
<PAGE>
                                      -25-


such right, license or franchise or the dissolution of such subsidiary does not
have a material adverse impact on the Holders.

SECTION 4.07. Notice of Default.

            In the event that any Default under Section 6.01 hereof shall occur
the Company will give prompt written notice of such Default to the Trustee.

                                  ARTICLE FIVE

                    CONSOLIDATION, MERGER AND SALE OF ASSETS

SECTION 5.01. When Company May Merge, etc.

            The Company shall not consolidate with or merge into, or transfer or
lease all or substantially all of its assets to, another Person unless such
other Person is a corporation, limited liability company, partnership, trust or
other business entity organized under the laws of the United States, any State
thereof or the District of Columbia and such Person assumes by supplemental
indenture all the obligations of the Company under the Securities, this
Indenture and the Registration Rights Agreement, and immediately after giving
effect to the transaction, no Default or Event of Default has occurred and is
continuing.

            The Company shall deliver to the Trustee prior to the consummation
of the proposed transaction an Officers' Certificate to the foregoing effect and
an Opinion of Counsel stating that the proposed transaction and such
supplemental indenture will, upon consummation of the proposed transaction,
comply with this Indenture.

            Notwithstanding the foregoing, any subsidiary may consolidate with,
merge into or transfer all or part of its properties and assets to the Company
or any other subsidiary or subsidiaries.

SECTION 5.02. Successor Substituted.

            Upon any consolidation or merger or transfer or lease of all or
substantially all of the assets of the Company in accordance with Section 5.01,
the successor Person formed by such consolidation or into which the Company is
merged or to which such transfer or lease is made shall succeed to, and be
substituted for, and may exercise every right and power of, and shall assume
every duty and obligation of, the Company under this Indenture with the same
effect as if such successor corporation had been named as the Company herein.
When the successor corporation assumes all obligations of the Company hereunder,
all obligations of the predecessor corporation shall terminate.
<PAGE>
                                      -26-


                                   ARTICLE SIX

                              DEFAULTS AND REMEDIES

SECTION 6.01. Events of Default.

            An "Event of Default" occurs if:

            (1) the Company fails to pay the principal of or any premium on the
      Securities when due (whether or not prohibited by the provisions set forth
      in Article Twelve hereof);

            (2) the Company fails to pay any interest on the Securities for 30
      days when due (whether or not prohibited by the provisions set forth in
      Article Twelve hereof);

            (3) the Company fails to perform any other covenant in this
      Indenture for the period and after the notice specified in the last
      paragraph of this Section 6.01;

            (4) the Company pursuant to or within the meaning of any Bankruptcy
      Law:

                  (A) commences a voluntary case,

                  (B) consents to the entry of an order for relief against it in
            an involuntary case,

                  (C) consents to the appointment of a Custodian of it or for
            all or substantially all of its property, or

                  (D) makes a general assignment for the benefit of its
            creditors; or

            (5) a court of competent jurisdiction enters an order or decree
      under any Bankruptcy Law that:

                  (A) is for relief against the Company in an involuntary case,

                  (B) appoints a Custodian of the Company for all or
            substantially all of its property, or

                  (C) orders the liquidation of the Company,

            and the order or decree remains unstayed and in effect for 90
            consecutive days.

            The term "Bankruptcy Law" means Title 11, U.S. Code or any similar
Federal or State law for the relief of debtors. The term "Custodian" means any
receiver trustee, assignee, liquidator or similar official under any Bankruptcy
Law.
<PAGE>
                                      -27-


            A default under clause (3) is not an Event of Default until the
Trustee or the Holders of at least 25% in aggregate principal amount of the
Securities then outstanding notify the Company and the Trustee of the default
and the Company does not cure the default within 90 days after receipt of the
notice of such default. The notice must specify the default, demand that it be
remedied and state that the notice is a "Notice of Default". If the Holders of
25% in aggregate principal amount of the outstanding Securities request the
Trustee to give such notice on their behalf, the Trustee shall do so. When a
default is cured, it ceases.

SECTION 6.02. Acceleration.

            If an Event of Default (other than an Event of Default specified in
Section 6.01(4) or (5)) occurs and is continuing, the Trustee by notice to the
Company, or the Holders of at least 25% in principal amount of the Securities
then outstanding by notice to the Company and the Trustee, may declare the
principal of, premium, if any, and any accrued and unpaid interest on all the
Securities to be due and payable. Upon such declaration such principal and
interest shall be due and payable immediately. If an Event of Default specified
in Section 6.01(4) or (5) occurs, the entire principal amount of the Securities
shall ipso facto become and be immediately due and payable without any
declaration or other act on the part of the Trustee or any Holder.

            The Company shall promptly notify holders of Designated Senior
Indebtedness if payment of the Securities is accelerated because of an Event of
Default.

            After a declaration of acceleration, but before a judgment or decree
of the money due in respect of the Securities has been obtained, the Holders of
not less than a majority in aggregate principal amount of the Securities then
outstanding by written notice to the Trustee may rescind an acceleration and its
consequences if (i) all existing Events of Default (other than the nonpayment of
principal of and interest on the Securities which has become due solely by
virtue of such acceleration) have been cured or waived, (ii) the rescission
would not conflict with any judgment or decree and (iii) the Company shall have
paid all amounts due pursuant to Section 7.07.

SECTION 6.03. Other Remedies.

            Notwithstanding any other provision of this Indenture, if an Event
of Default occurs and is continuing, the Trustee may pursue any available remedy
by proceeding at law or in equity to collect the payment of the principal of,
premium, if any, and interest on the Securities or to enforce the performance of
any provision of the Securities or this Indenture.

            The Trustee may maintain a proceeding even if it does not possess
any of the Securities or does not produce any of them in the proceeding. A delay
or omission by the Trustee or any Holder in exercising any right or remedy
accruing upon an Event of Default shall not impair the right or remedy or
constitute a waiver of or acquiescence in the Event of Default. All remedies are
cumulative.
<PAGE>
                                      -28-


SECTION 6.04. Waiver of Past Defaults.

            Subject to Sections 6.02, 6.07 and 9.02, the Holders of a majority
in aggregate principal amount of the Securities then outstanding by notice to
the Trustee may waive any past Default or Event of Default and its consequences.
When a Default or an Event of Default is waived, it is cured and ceases.

SECTION 6.05. Control by Majority.

            The Holders of a majority in aggregate principal amount of the
Securities then outstanding may direct the time, method and place of conducting
any proceeding for any remedy available to the Trustee or exercising any trust
or power conferred on it. However, the Trustee may refuse to follow any
direction that conflicts with law or this Indenture, is unduly prejudicial to
the rights of other Holders or would involve the Trustee in personal liability;
provided that the Trustee may take any other action deemed proper by the Trustee
which is not inconsistent with such direction.

SECTION 6.06. Limitation on Suits.

            Except as provided in Section 6.07, a Holder may pursue a remedy
with respect to this Indenture or the Securities only if:

            (1) the Holder gives to the Trustee written notice of a continuing
      Event of Default;

            (2) the Holders of at least 25% in aggregate principal amount of the
      Securities then outstanding make a written request to the Trustee to
      pursue the remedy;

            (3) such Holder or Holders offer to the Trustee indemnity
      satisfactory to the Trustee against any loss, liability or expense;

            (4) the Trustee does not comply with the request within 60 days
      after receipt of the request and the offer of indemnity; and

            (5) during such 60-day period the Holders of a majority in aggregate
      principal amount of the Securities then outstanding do not give the
      Trustee a direction inconsistent with the request.

            A Holder may not use this Indenture to prejudice the rights of
another Holder or to obtain a preference or priority over another Holder.

SECTION 6.07. Rights of Holders to Receive Payment or Convert.

            Notwithstanding any other provision of this Indenture, (i) the right
of any Holder to receive payment of the principal of and interest on the
Security, on or after the respective due dates expressed in the Security, or to
bring suit for the enforcement of any such payment on or after such
<PAGE>
                                      -29-


respective dates, shall not be impaired or affected without the consent of the
Holder and (ii) the right of any Holder to bring suit for the enforcement of the
right to convert the Security shall not be impaired or affected without the
consent of the Holder.

SECTION 6.08. Collection Suit by Trustee.

            If an Event of Default specified in Section 6.01(1) or (2) occurs
and is continuing, the Trustee may recover judgment in its own name and as
trustee of an express trust against the Company for the whole amount of
principal and interest remaining unpaid and amounts due to the Trustee under
Section 7.07.

SECTION 6.09. Trustee May File Proofs of Claim.

            The Trustee may file such proofs of claim and other papers or
documents as may be necessary or advisable in order to have the claims of the
Trustee, any predecessor Trustee and the Holders allowed in any judicial
proceedings relative to the Company, its creditors or its property.

            Nothing herein contained shall be deemed to authorize the Trustee to
authorize or consent to or accept or adopt on behalf of any Holder any plan of
reorganization, arrangement, adjustment or composition affecting the Securities
or the rights of any Holder thereof, or to authorize the Trustee to vote in
respect of the claim of any Holder in any such proceeding.

SECTION 6.10. Priorities.

            If the Trustee collects any money pursuant to this Article, it shall
pay out the money in the following order:

            First: to the Trustee for amounts due under Section 7.07;

            Second: to holders of Senior Indebtedness to the extent required by
      Article Twelve;

            Third: to Holders for amounts due and unpaid on the Securities for
      principal, premium, if any, and interest, ratably, without preference or
      priority of any kind, according to the amounts due and payable on the
      Securities for principal, premium, if any, and interest, respectively, and

            Fourth: to the Company.

            The Trustee, upon prior written notice to the Company, may fix a
record date and payment date for any payment by it to Holders pursuant to this
Section 6.10.

SECTION 6.11. Undertaking for Costs.

            In any suit for the enforcement of any right or remedy under this
Indenture or in any suit against the Trustee for any action taken or omitted by
it as Trustee, a court in its discretion may
<PAGE>
                                      -30-


require the filing by any party litigant in the suit other than the Trustee of
an undertaking to pay the costs of the suit, and the court in its discretion may
assess reasonable costs, including reasonable attorneys' fees, against any party
litigant in the suit, having due regard to the merits and good faith of the
claims or defenses made by the party litigant. This Section 6.11 shall not apply
to a suit by the Trustee, a suit by a Holder or group of Holders of more than
10% in aggregate principal amount of the outstanding Securities, or to any suit
instituted by any Holder for the enforcement or the payment of the principal or
interest on any Securities on or after the respective due dates for such
Securities.

                                  ARTICLE SEVEN

                                     TRUSTEE

SECTION 7.01. Duties of Trustee.

            (a) If an Event of Default has occurred and is continuing, the
Trustee shall exercise such of the rights and powers vested in it by this
Indenture, and use the same degree of care and skill in their exercise, as a
prudent person would exercise or use under the circumstances in the conduct of
his or her own affairs.

            (b) Except during the continuance of an Event of Default:

            (1) the Trustee need perform only those duties that are specifically
      set forth in this Indenture and no others; and

            (2) in the absence of bad faith on its part, the Trustee may
      conclusively rely, as to the truth of the statements and the correctness
      of the opinions expressed therein, upon certificates or opinions furnished
      to the Trustee and conforming to the requirements of this Indenture, but
      in the case of any such certificates or opinions which by any provision
      hereof are specifically required to be furnished to the Trustee, the
      Trustee shall examine the certificates and opinions to determine whether
      or not they conform to the requirements of this Indenture.

            (c) The Trustee may not be relieved from liability for its own
negligent action, its own negligent failure to act or its own willful
misconduct, except that:

            (1) this paragraph does not limit the effect of paragraph (b) of
      this Section 7.01;

            (2) the Trustee shall not be liable for any error of judgment made
      in good faith by a Trust Officer, unless it is proved that the Trustee was
      negligent in ascertaining the pertinent facts; and

            (3) the Trustee shall not be liable with respect to any action it
      takes or omits to take in good faith in accordance with a direction
      received by it pursuant to Section 6.05.
<PAGE>
                                      -31-


            (d) The Trustee may refuse to perform any duty or exercise any right
or power unless it receives indemnity satisfactory to it against any loss,
liability or expense.

            (e) The Trustee shall not be liable for interest on any money
received by it except as the Trustee may agree in writing with the Company.
Money held in trust by the Trustee need not be segregated from other funds
except to the extent required by law.

SECTION 7.02. Rights of Trustee.

            (a) The Trustee may rely on any document believed by it to be
genuine and to have been signed or presented by the proper person. The Trustee
need not investigate any fact or matter stated in the document; if, however, the
Trustee shall determine to make such further inquiry or investigation, it shall
be entitled to examine the books, records and premises of the Company,
personally or by agent or attorney.

            (b) Before the Trustee acts or refrains from acting, it may require
an Officers' Certificate and/or an Opinion of Counsel. The Trustee shall not be
liable for any action it takes or omits to take in good faith in reliance on
such Officers' Certificate or Opinion of Counsel.

            (c) Any request or direction of the Company mentioned herein shall
be sufficiently evidenced by a Company Request or Company Order and any
resolution of the Board of Directors shall be sufficiently evidenced by a Board
Resolution.

            (d) The Trustee may consult with counsel (such counsel to be
reasonably acceptable to the Company) and the written advice of such counsel or
any Opinion of Counsel shall be full and complete authorization and protection
in respect of any action taken, suffered or omitted by it hereunder in good
faith and in reliance thereon.

            (e) The Trustee may act through agents or attorneys and shall not be
responsible for the misconduct or negligence of any agent or attorney appointed
with due care.

            (f) The Trustee shall not be liable for any action it takes or omits
to take in good faith which it believes to be authorized or within its
discretion, rights or powers hereunder.

            (g) Whenever in the administration of this Indenture the Trustee
shall deem it desirable that a matter be proved or established prior to taking,
suffering or omitting any action hereunder, the Trustee may, in absence of bad
faith on its part, rely upon an Officers' Certificate.

            (h) The Trustee shall be under no obligation to exercise any of the
rights or powers vested in it by this Indenture at the request or direction of
any of the Holders, unless such Holders shall have offered to the Trustee
reasonable security or indemnity against costs, expenses and liabilities that
might be incurred by it in compliance with such request or direction.

            (i) The Trustee shall not be charged with knowledge of any Default
or Event of Default with respect to the Securities unless either (1) a Trust
Officer shall have actual knowledge of
<PAGE>
                                      -32-


such Default or Event of Default or (2) written notice of such Default or Event
of Default shall have been given to the Trustee by the Company or by any Holder.

SECTION 7.03. Individual Rights of Trustee.

            The Trustee in its individual or any other capacity may become the
owner or pledgee of Securities and may otherwise deal with the Company or an
Affiliate thereof with the same rights it would have if it were not Trustee. Any
Agent may do the same with like rights. The Trustee, however, must comply with
Sections 7.10 and 7.11.

SECTION 7.04. Trustee's Disclaimer.

            The Trustee makes no representation as to the validity or adequacy
of this Indenture or the Securities; it shall not be accountable for the
Company's use of the proceeds from the Securities; and it shall not be
responsible for any statement in the Securities other than its certificate of
authentication.

SECTION 7.05. Notice of Defaults.

            If a Default or Event of Default occurs and is continuing and if it
is actually known to the Trustee, the Trustee shall mail to each Holder a notice
of the Default or Event of Default within 30 days after it occurs unless such
Default or Event of Default has been cured or waived. Except in the case of a
Default or Event of Default in payment of the principal of, premium, if any, and
interest on any Security, the Trustee may withhold the notice if and so long as
it in good faith determines that withholding the notice is in the interests of
Holders.

SECTION 7.06. Reports by Trustee to Holders.

            Within 60 days after each May 15 beginning with May 15, 2001, the
Trustee shall mail to each Holder, to the extent required by TIA ss. 313(c), a
brief report dated as of such March 1 that complies with TIA ss. 313(a). In such
event, the Trustee also shall comply with TIA ss. 313(b).

            A copy of each report at the time of its mailing to Holders shall be
mailed to the Company and filed by the Trustee with the SEC and each stock
exchange, if any, on which the Securities are listed. The Company shall promptly
notify the Trustee when the Securities are listed on any stock exchange.

SECTION 7.07. Compensation and Indemnity.

            The Company shall pay to the Trustee from time to time such
compensation for its services as shall be agreed upon in writing. The Trustee's
compensation shall not be limited by any law on compensation of a trustee of an
express trust. The Company shall reimburse the Trustee upon request for all
reasonable out-of-pocket expenses incurred by it. Such expenses shall include
the reasonable compensation and out-of-pocket expenses of the Trustee's agents
and counsel.
<PAGE>
                                      -33-


            The Company shall indemnify the Trustee against any loss or
liability or expense (including the reasonable fees and expenses of counsel)
incurred by it in connection with the acceptance or administration of this trust
and the performance of its duties hereunder, including the reasonable costs and
expenses of defending itself against any claim or liability in connection with
the exercise or performance of any of its powers and duties hereunder. The
Company need not pay for any settlement made without its consent. The Trustee
shall notify the Company promptly of any claim for which it may seek
indemnification. The Company need not reimburse any expense or indemnify against
any loss or liability incurred by the Trustee through the Trustee's negligence
or bad faith.

            To secure the Company's payment obligations in this Section 7.07,
the Trustee shall have a lien prior to the Securities on all money or property
held or collected by the Trustee, except that held in trust to pay the principal
of, premium, if any, and interest on particular Securities.

            The indemnity obligations of the Company with respect to the Trustee
provided for in this Section 7.07 shall survive any resignation or removal of
the Trustee and the termination of this Indenture.

            When the Trustee incurs expenses or renders services after an Event
of Default specified in Section 6.01(4) or (5) occurs, the expenses and the
compensation for the services are intended to constitute expenses of
administration under any Bankruptcy Law.

SECTION 7.08. Replacement of Trustee.

            A resignation or removal of the Trustee and appointment of a
successor Trustee shall become effective only upon the successor Trustee's
acceptance of appointment as provided in this Section 7.08.

            The Trustee may resign by so notifying the Company in writing 30
days prior to such resignation. The Holders of a majority in aggregate principal
amount of the Securities then outstanding may remove the Trustee by so notifying
the Trustee and the Company in writing and may appoint a successor Trustee with
the Company's consent. The Company may remove the Trustee if:

            (1) the Trustee fails to comply with Section 7.10;

            (2) the Trustee is adjudged a bankrupt or an insolvent;

            (3) a receiver or other public officer takes charge of the Trustee
      or its property; or

            (4) the Trustee becomes incapable of acting.

            If the Trustee resigns or is removed or if a vacancy exists in the
office of Trustee for any reason, the Company shall promptly appoint a successor
Trustee. Within one year after the successor Trustee takes office, the Holders
of a majority in aggregate principal amount of the Securities
<PAGE>
                                      -34-


then outstanding may appoint a successor Trustee to replace the successor
Trustee appointed by the Company.

            If a successor Trustee does not take office within 30 days after the
retiring Trustee resigns or is removed, the retiring Trustee, the Company or the
Holders of at least 10% in aggregate principal amount of the outstanding
Securities may petition any court of competent jurisdiction for the appointment
of a successor Trustee.

            If the Trustee fails to comply with Section 7.10, any Holder may
petition any court of competent jurisdiction for the removal of the Trustee and
the appointment of a successor Trustee.

            A successor Trustee shall deliver a written acceptance of its
appointment to the retiring Trustee and to the Company. Thereupon the
resignation or removal of the retiring Trustee shall become effective, and the
successor Trustee shall have all the rights, powers and duties of the Trustee
under this Indenture. The successor Trustee shall mail a notice of its
succession to Holders. The retiring Trustee shall promptly transfer all property
held by it as Trustee to the successor Trustee, subject to the lien provided for
in Section 7.07.

SECTION 7.09. Successor Trustee by Merger, etc.

            If the Trustee consolidates with, merges or converts into, or
transfers all or substantially all of its corporate trust business to, another
corporation, the successor corporation without any further act shall be the
successor Trustee, if such successor corporation is otherwise eligible
hereunder.

SECTION 7.10. Eligibility; Disqualification.

            This Indenture shall always have a Trustee who satisfies the
requirements of TIA ss. 310(a)(1). The Trustee shall always have a combined
capital and surplus of at least $50,000,000 as set forth in its most recent
published annual report of condition. The Trustee shall comply with TIA ss.
310(b).

SECTION 7.11. Preferential Collection of Claims Against Company.

             The Trustee shall comply with TIA ss. 311(a), excluding any
creditor relationship listed in TIA ss. 311(b). A Trustee who has resigned or
been removed shall be subject to TIA ss. 311(a) to the extent indicated.
<PAGE>
                                      -35-


                                  ARTICLE EIGHT

                     SATISFACTION AND DISCHARGE; DEFEASANCE

SECTION 8.01. Termination of Company's Obligations.

            The Company may terminate its substantive obligations in respect of
the Securities if the Securities mature within six months, or all of them are to
be called for redemption within one year under arrangements satisfactory to the
Trustee for giving notice of redemption, by delivering all outstanding
Securities to the Trustee for cancellation and paying all sums payable by it on
account of principal of, premium, if any, and interest on all Securities or
otherwise. In addition to the foregoing, the Company may terminate its
obligations under Sections 3.07, 4.03 and 4.06 (other than with respect to the
corporate existence of the Company), and no Default or Event of Default under
Section 6.01(3) shall thereafter apply, by (i) depositing with the Trustee,
under the terms of an irrevocable trust agreement, money or direct non-callable
obligations of the United States of America for the payment of which the full
faith and credit of the United States is pledged ("U.S. Government
Obligations") sufficient (without reinvestment) to pay the principal of,
premium, if any, and interest on the Securities at maturity or an earlier
redemption, (ii) delivering to the Trustee either an Opinion of Counsel or a
ruling directed to the Trustee from the Internal Revenue Service to the effect
that the Holders of the Securities will not recognize income, gain or loss for
federal income tax purposes as a result of such deposit and termination of
obligations and (iii) delivering to the Trustee an Officers' Certificate and an
Opinion of Counsel each stating compliance with all conditions precedent
provided for herein. In addition, the Company may, provided that no Default or
Event of Default has occurred and is continuing or would arise therefrom (or,
with respect to a Default or Event of Default specified in Section 6.01(4),
occurs at any time on or prior to the 91st calendar day after the date of such
deposit (it being understood that this condition shall not be deemed satisfied
until after such 91st day)), terminate all of its substantive obligations in
respect of the Securities (including its obligations to pay the principal of,
premium, if any, and interest on the Securities) by (i) depositing with the
Trustee, under the terms of an irrevocable trust agreement, money or United
States Government Obligations sufficient (without reinvestment) to pay the
principal of, premium, if any, and interest on the Securities at maturity or on
earlier redemption, (ii) delivering to the Trustee either a ruling directed to
the Trustee from the Internal Revenue Service to the effect that the Holders of
the Securities will not recognize income, gain or loss for federal income tax
purposes as a result of such deposit and termination of obligations or an
Opinion of Counsel addressed to the Trustee based upon such a ruling or based on
a change in the applicable Federal tax law since the date of this Indenture to
such effect and (iii) delivering to the Trustee an Officers' Certificate and an
Opinion of Counsel each stating compliance with all conditions precedent
provided for herein.

            Notwithstanding the foregoing paragraph, the Company's obligations
in Article Ten and Sections 2.02, 2.03, 2.04, 2.05, 2.06, 2.07, 2.10, 2.12, 2.13
and 4.01 (but not with respect to termination of substantive obligations
pursuant to the third sentence of the foregoing paragraph), 4.02, 7.07, 7.08,
8.03 and 8.04 shall survive until the Securities are no longer outstanding.
Thereafter the Company's obligations in Sections 7.07, 8.03 and 8.04 shall
survive.
<PAGE>
                                      -36-


            After such delivery or irrevocable deposit and delivery of an
Officers' Certificate and Opinion of Counsel, the Trustee upon request shall
acknowledge in writing the discharge of the Company's obligations under the
Securities and this Indenture except for those surviving obligations specified
above.

            The Company shall pay and indemnify the Trustee against any tax, fee
or other charge imposed on or assessed against the United States Government
Obligations deposited pursuant to this Section 8.01 or the principal and
interest received in respect thereof other than any such tax, fee or other
charge which by law is for the account of the Holders of outstanding Securities.

SECTION 8.02. Application of Trust Money.

            Subject to the provisions of Section 8.03, the Trustee shall hold in
trust money or U.S. Government Obligations deposited with it pursuant to Section
8.01. It shall apply the deposited money and the money from U.S. Government
obligations through the Paying Agent and in accordance with this Indenture to
the payment of the principal of, premium, if any, and interest on the
Securities. Money and securities so held in trust are not subject to the
subordination provisions of Article Twelve.

SECTION 8.03. Repayment to Company.

            The Trustee and the Paying Agent shall promptly pay to the Company
upon request any excess money or securities held by them at any time. The
Trustee and the Paying Agent shall pay to the Company upon request any money
held by them for the payment of the principal of, premium, if any, and interest
that remains unclaimed for two years; provided, however, that the Trustee or
such Paying Agent, before being required to make any such repayment, may, at the
expense of the Company, cause to be published once in a newspaper of general
circulation in The City of New York or cause to be mailed to each Holder, notice
stating that such money remains and that, after a date specified therein, which
shall not be less than 30 days from the date of such publication or mailing, any
unclaimed balance of such money then remaining will be repaid to the Company.
After payment to the Company, Holders entitled to the money must look to the
Company for payment as general creditors unless an applicable abandoned property
law designates another Person.

SECTION 8.04. Reinstatement.

            If the Trustee or Paying Agent is unable to apply any money or U.S.
Government Obligations in accordance with Section 8.01 by reason of any legal
proceeding or by reason of any order or judgment of any court or governmental
authority enjoining, restraining or otherwise prohibiting such application, the
Company's obligations under this Indenture and the Securities shall be revived
and reinstated as though no deposit had occurred pursuant to Section 8.01 until
such time as the Trustee or Paying Agent is permitted to apply all such money or
U.S. Government Obligations in accordance with Section 8.01; provided, however,
that to the extent the Company makes any payment of the principal of, premium,
if any, and interest on any Securities because of the reinstatement of its
obligations, the Company shall be subrogated to the rights of the Holders of
such Securities to receive such payment from the money or U.S. Government
Obligations held by the Trustee or Paying Agent.
<PAGE>
                                      -37-


                                  ARTICLE NINE

                                   AMENDMENTS

SECTION 9.01. Without Consent of Holders.

            The Company, when authorized by a Board Resolution, may modify,
amend or supplement this Indenture or the Securities without notice to or the
consent of any Holder:

            (1) to cure any ambiguity, omission, defect or inconsistency;

            (2) to comply with Sections 5.01 and 10.07;

            (3) to provide for uncertificated Securities in addition to
      certificated Securities; or

            (4) to make any change that does not adversely affect the rights of
      any Holder.

SECTION 9.02. With Consent of Holders.

            The Company, when authorized by a Board Resolution, may modify,
amend or supplement this Indenture or the Securities without notice to any
Holder but with the written consent of the Holders of at least a majority in
aggregate principal amount of the outstanding Securities. Subject to Section
6.07, the Holders of a majority in aggregate principal amount of the outstanding
Securities may waive compliance by the Company with any provision of this
Indenture or the Securities without notice to any other Holder. However, without
the consent of each Holder affected, an amendment, supplement or waiver,
including a waiver pursuant to Section 6.04, may not:

            (1) change the stated maturity of the Securities:

            (2) reduce the principal, premium, if any. or interest on the
      Securities:

            (3) change the place of payment from New York, New York or change
      the currency in which the Securities are payable;

            (4) waive a default in the payment of the principal of, premium, if
      any, or interest on any Security;

            (5) make any change in Section 6.04, Section 6.07 or this Section
      9.02;

            (6) modify the provisions of Article Twelve in a materially adverse
      manner to the Holders; or

            (7) make any change that adversely affects the right to convert any
      Security.
<PAGE>
                                      -38-


            Furthermore, an amendment under this Article Nine may not make any
change that adversely affects the rights of any holder of Senior Indebtedness
under Article Twelve unless the holders of such Senior Indebtedness consent to
such change pursuant to the terms governing such Senior Indebtedness. It shall
not be necessary for the consent of the Holders under this Section 9.02 to
approve the particular form of any proposed amendment or supplement, but it
shall be sufficient if such consent approves the substance thereof.

            Promptly after an amendment under this Section 9.02 becomes
effective, the Company shall mail to Holders a notice briefly describing the
amendment.

SECTION 9.03. Compliance with Trust Indenture Act.

            Every amendment, waiver or supplement to this Indenture or the
Securities shall comply with the TIA as then in effect.

SECTION 9.04. Revocation and Effect of Consents.

            Until an amendment, supplement or waiver becomes effective, a
consent to it by a Holder is a continuing consent by the Holder and every
subsequent Holder of a Security or portion of a Security that evidences the same
debt as the consenting Holder's Security, even if notation of the consent is not
made on any Security. However, any such Holder or subsequent Holder may revoke
the consent as to its Security or portion of a Security if the Trustee receives
the notice of revocation before the date the amendment, supplement or waiver
becomes effective. An amendment, supplement or waiver becomes effective in
accordance with its terms and thereafter binds every Holder.

            After an amendment, supplement or waiver becomes effective with
respect to the Securities, it shall bind every Holder unless it makes a change
described in any of clauses (1) through (7) of Section 9.02. In that case the
amendment, supplement or waiver shall bind each Holder of a Security who has
consented to it and, provided that notice of such amendment, supplement or
waiver is reflected on a Security that evidences the same debt as the consenting
Holder's Security, every subsequent Holder of a Security or portion of a
Security that evidences the same debt as the consenting Holder's Security.

SECTION 9.05. Notation on or Exchange of Securities.

            If an amendment, supplement or waiver changes the terms of a
Security, the Trustee may require the Holder of the Security to deliver it to
the Trustee. The Trustee may place an appropriate notation on the Security as
directed and prepared by the Company about the changed terms and return it to
the Holder. Alternatively, if the Company so determines, the Company in exchange
for the Security shall issue and the Trustee shall authenticate a new Security
that reflects the changed terms.
<PAGE>
                                      -39-


SECTION 9.06. Trustee Protected.

            The Trustee need not sign any amendment, supplement or waiver
authorized pursuant to this Article that adversely affects the Trustee's rights.
The Trustee shall be entitled to receive and rely upon, in addition to the
documents required by Section 13.04, an Opinion of Counsel and an Officers'
Certificate that any supplemental indenture, modification, amendment or waiver
complies with the Indenture.

                                   ARTICLE TEN

                                   CONVERSION

SECTION 10.01. Conversion Privilege; Restrictive Legends.

            A Holder of a Security may convert the principal of such Security
into Common Stock at any time during the period stated in paragraph 9 of the
Securities. The number of shares issuable upon conversion of a Security is
determined as follows: divide each $1,000 of the principal amount to be
converted by the Conversion Price in effect on the conversion date and round the
result to the nearest 1/100th of a share. The Conversion Price is subject to
adjustment in accordance with Section 10.06.

            A Holder may convert a portion of the principal of such Security if
the portion is at least $1,000 principal amount or a whole multiple of $1,000
principal amount. Provisions of this Indenture that apply to conversion of all
of a Security also apply to conversion of a portion of it.

            Any shares issued upon conversion of a Security shall bear the
Private Placement Legend set forth in Exhibit B(I) until after the second
anniversary of the later of the Issue Date for such Security and the last date
on which the Company or any Affiliate of the Company was the owner of such
shares or the Security (or any predecessor security) from which such shares were
converted (or such shorter period of time as permitted by Rule 144(k) under the
Securities Act or any successor provision thereunder or such longer period of
time as may be required under the Securities Act or applicable state securities
laws unless otherwise agreed by the Company and the Holder thereof).

SECTION 10.02. Conversion Procedure.

            To convert a Security a Holder must satisfy the requirements in
paragraph 9 of the Securities. The date on which the Holder satisfies all those
requirements is the conversion date. As soon as practicable, the Company shall
deliver to the Holder through the Conversion Agent a certificate for the number
of full shares of Common Stock issuable upon the conversion and a check in lieu
of any fractional share. The Person in whose name the certificate is registered
shall be treated as a stockholder of record on and after the conversion date.
<PAGE>
                                      -40-


            Except as described below, no payment or adjustment will be made for
accrued interest on, or liquidated damages with respect to, a converted Security
or for dividends on any Common Stock issued on conversion. If any Security is
converted between a record date for the payment of interest and the next
succeeding interest payment date, unless such Security has been called for
redemption on a redemption date between such dates, such Security must be
accompanied by funds equal to the interest payable to the registered Holder on
such interest payment date on the principal amount so converted. A Security
converted on an interest payment date need not be accompanied by any payment,
and the interest on the principal amount of the Security being converted will be
paid on such interest payment date to the registered Holder of such Security on
the applicable record date.

            If a Holder converts more than one Security at the same time, the
number of full shares issuable upon the conversion shall be based on the total
principal amount of the Securities converted.

            Upon surrender of a Security that is converted in part the Trustee
shall authenticate for the Holder a new Security equal in principal amount to
the unconverted portion of the Security surrendered.

            If the last day on which a Security may be converted is a Legal
Holiday in a place where a Conversion Agent is located, the Security may be
surrendered to that Conversion Agent on the next succeeding day that is not a
Legal Holiday.

SECTION 10.03. Fractional Shares.

            The Company will not issue fractional shares of Common Stock upon
conversion of Securities and instead will deliver a check in lieu of the
fractional share based upon the current market value of the Common Stock. The
current market value of a fraction of a share is determined by multiplying the
current market price of a full share by the fraction, and rounding the result to
the nearest cent. For purposes of this Section, the current market price of a
share of Common Stock is the Closing Price of the Common Stock on the Trading
Day immediately preceding the conversion date.

SECTION 10.04. Taxes on Conversion.

            If a Holder converts its Security, the Company shall pay any
documentary, stamp or similar issue or transfer tax due on the issue of shares
of Common Stock upon the conversion. However, the Holder shall pay any such tax
which is due because the shares are issued in a name other than the Holder's
name.

SECTION 10.05. Company to Provide Stock.

            The Company shall reserve out of its authorized but unissued Common
Stock or its Common Stock held in treasury enough shares of Common Stock to
permit the conversion of all of the Securities, including such greater number of
shares of Common Stock into which such Securities shall be convertible into as a
result of a Conversion Price adjustment contemplated by Section 10.06 hereof.
<PAGE>
                                      -41-


            All shares of Common Stock which may be issued upon conversion of
the Securities shall be validly issued, fully paid and non-assessable.

            The Company will endeavor to comply with all securities laws
regulating the offer and delivery of shares of Common Stock upon conversion of
Securities and will endeavor to list such shares on each national securities
exchange on which the Common Stock is listed.

SECTION 10.06. Adjustment of Conversion Price.

            The Conversion Price shall be adjusted from time to time by the
Company as follows:

            (a) In case the Company shall hereafter pay a dividend or make a
      distribution to all holders of the outstanding Common Stock in shares of
      Common Stock, the Conversion Price in effect at the opening of business on
      the date following the Record Date with respect to stockholders entitled
      to receive such dividend or other distribution shall be reduced by
      multiplying such Conversion Price by a fraction of which the numerator
      shall be the number of shares of Common Stock outstanding at the close of
      business on the Record Date fixed for such determination and the
      denominator shall be the sum of such number of shares and the total number
      of shares constituting such dividend or other distribution, such reduction
      to become effective immediately after the opening of business on the day
      following the Record Date. If any dividend or distribution of the type
      described in this Section 10.06(a) is declared but not so paid or made,
      the Conversion Price shall again be adjusted to the Conversion Price which
      would then be in effect if such dividend or distribution had not been
      declared.

            (b) In case the Company shall issue rights or warrants to all
      holders of its outstanding shares of Common Stock entitling them to
      subscribe for or purchase shares of Common Stock at a price per share less
      than the Current Market Price on the Record Date fixed for the
      determination of stockholders entitled to receive such rights or warrants,
      the Conversion Price shall be adjusted so that the same shall equal the
      price determined by multiplying the Conversion Price in effect at the
      opening of business on the date after such Record Date by a fraction of
      which the numerator shall be the number of shares of Common Stock
      outstanding at the close of business on the Record Date plus the number of
      shares which the aggregate offering price of the total number of shares so
      offered for subscription or purchase would purchase at such Current Market
      Price, and of which the denominator shall be the number of shares of
      Common Stock outstanding on the close of business on the Record Date plus
      the total number of additional shares of Common Stock so offered for
      subscription or purchase. Such adjustment shall become effective
      immediately after the opening of business on the day following the Record
      Date fixed for determination of stockholders entitled to receive such
      rights or warrants. To the extent that shares of Common Stock are not
      delivered pursuant to such rights or warrants, upon the expiration or
      termination of such rights or warrants the Conversion Price shall be
      readjusted to the Conversion Price which would then be in effect had the
      adjustments made upon the issuance of such rights or warrants been made on
      the basis of delivery of only the number of shares of Common Stock
      actually delivered. In the event that such rights or warrants are not so
      issued, the Conversion Price shall again be adjusted to be the Conversion
<PAGE>
                                      -42-


      Price which would then be in effect if such date fixed for the
      determination of stockholders entitled to receive such rights or warrants
      had not been fixed. In determining whether any rights or warrants entitle
      the holders to subscribe for or purchase shares of Common Stock at less
      than such Current Market Price, and in determining the aggregate offering
      price of such shares of Common Stock, there shall be taken into account
      any consideration received for such rights or warrants, the value of such
      consideration, if other than cash, to be determined in good faith by the
      Board of Directors.

            (c) In case the outstanding shares of Common Stock shall be split or
      subdivided into a greater number of shares of Common Stock, the Conversion
      Price in effect at the opening of business on the day following the day
      upon which such subdivision becomes effective shall be proportionately
      reduced, and conversely, in case outstanding shares of Common Stock shall
      be combined into a smaller number of shares of Common Stock, the
      Conversion Price in effect at the opening of business on the day following
      the day upon which such combination becomes effective shall be
      proportionately increased, such reduction or increase, as the case may be,
      to become effective immediately after the opening of business on the day
      following the day upon which such subdivision or combination becomes
      effective.

            (d) In case the Company shall, by dividend or otherwise, distribute
      to all holders of its Common Stock shares of any class of capital stock of
      the Company (other than any dividends or distributions to which Section
      10.06(a) applies) or evidences of its indebtedness, cash or other assets
      (including securities, but excluding (1) any rights or warrants referred
      to in Section 10.06(b), (2) dividends and distributions (A) in connection
      with the liquidation, dissolution or winding up of the Company or (B) paid
      exclusively in cash and (3) any capital stock, evidences of indebtedness,
      cash or assets distributed upon a merger or consolidation to which Section
      10.07 applies) (the foregoing hereinafter in this Section 10.06(d) called
      the "Subject Securities"), unless the Company elects to reserve such
      Subject Securities for distribution to the Holders upon conversion of the
      Securities so that any such Holder converting Securities will receive upon
      such conversion, in addition to the shares of Common Stock to which such
      Holder is entitled, the amount and kind of such Subject Securities which
      such Holder would have received if such Holder had converted its
      Securities into Common Stock immediately prior to the Record Date for such
      distribution of the Subject Securities, then, in each such case, the
      Conversion Price shall be reduced so that the same shall be equal to the
      price determined by multiplying the Conversion Price in effect immediately
      prior to the close of business on the Record Date with respect to such
      distribution by a fraction of which the numerator shall be the Current
      Market Price on such date less the fair market value on such date of the
      portion of the Subject Securities so distributed applicable to one share
      of Common Stock and the denominator shall be such Current Market Price,
      such reduction to become effective immediately prior to the opening of
      business on the day following the Record Date; provided, however, that in
      the event the then fair market value of the portion of the Subject
      Securities so distributed applicable to one share of Common Stock is equal
      to or greater than the Current Market Price on the Record Date, then in
      lieu of the foregoing adjustment, adequate provision shall be made so that
      each Holder shall have the right to receive upon conversion of a Security
      (or any portion thereof) the amount of Subject Securities such Holder
<PAGE>
                                      -43-


      would have received had such Holder converted such Security (or portion
      thereof) immediately prior to such Record Date. In the event that such
      dividend or distribution is not so paid or made, the Conversion Price
      shall again be adjusted to be the Conversion Price which would then be in
      effect if such dividend or distribution had not been declared.

            For purposes of this Section 10.06(d), rights or warrants
      distributed by the Company to all holders of Common Stock entitling the
      holders thereof to subscribe for or purchase shares of the Company's
      capital stock (either initially or under certain circumstances) that are
      (i) deemed to be transferred with such shares of Common Stock; (ii) not
      exercisable; and (iii) issued in respect of future issuances of Common
      Stock, until the occurrence of a specified event or events ("Trigger
      Event") shall be deemed not to have been distributed and no adjustment to
      the Conversion Price with respect thereto shall be made until the
      occurrence of the earliest Trigger Event. If any such right or warrant is
      subject to subsequent events, upon the occurrence of which such right or
      warrant shall become exercisable to purchase different securities,
      evidences of indebtedness or other assets or entitle the holder to
      purchase a different number or amount of the foregoing or to purchase any
      of the foregoing at a different purchase price, then the occurrence of
      each such event shall be deemed to be the date of issuance and record date
      with respect to a new right or warrant (and a termination or expiration of
      the existing right or warrant without exercise by the holder thereof). In
      addition, in the event of any distribution (or deemed distribution) of
      rights or warrants, or any Trigger Event or other event (of the type
      described in the preceding sentence) with respect thereto, that resulted
      in an adjustment to the Conversion Price under this Section 10.06(d), (1)
      in the case of any such rights or warrants which shall all have been
      redeemed or repurchased without exercise by any holders thereof, the
      Conversion Price shall be readjusted upon such final redemption or
      repurchase to give effect to such distribution or Trigger Event, as the
      case may be, as though it were a cash distribution, equal to the per share
      redemption or repurchase price received by a holder of Common Stock with
      respect to such rights or warrants (assuming such holder had retained such
      rights or warrants), made to all holders of Common Stock as of the date of
      such redemption or repurchase, and (2) in the case of such rights or
      warrants all of which shall have expired or been terminated without
      exercise, the Conversion Price shall be readjusted as if such rights and
      warrants had never been issued.

            For purposes of this Section 10.06(d) and Sections 10.06(a) and (b),
      any dividend or distribution to which this Section 10.06(d) is otherwise
      applicable that also includes shares of Common Stock, or rights or
      warrants to subscribe for or purchase shares of Common Stock applies (or
      both), shall be deemed instead to be (1) a dividend or distribution of the
      evidences of indebtedness, assets, shares of capital stock, rights or
      warrants (other than such shares of Common Stock or rights or warrants)
      (and any Conversion Price reduction required by this Section 10.06(d) with
      respect to such dividend or distribution shall then be made) immediately
      followed by (2) a dividend or distribution of such shares of Common Stock
      or such rights or warrants (and any further Conversion Price reduction
      required by Sections 10.06(a) and (b) with respect to such dividend or
      distribution shall then be made), except (A) the Record Date of such
      dividend or distribution shall be substituted as "the date fixed for the
      determination of stockholders entitled to receive such dividend or other
      distribution", "Record
<PAGE>
                                      -44-


Date fixed for such determination" and "Record Date" within the meaning of
Section 10.06(a) and as "the date fixed for the determination of stockholders
entitled to receive such rights or warrants", "the Record Date fixed for the
determination of the stockholders entitled to receive such rights or warrants"
and "such Record Date" within the meaning of Section 10.06(b) and (B) any shares
of Common Stock included in such dividend or distribution shall not be deemed
"outstanding at the close of business on the Record Date fixed for such
determination" within the meaning of Section 10.06(a).

      With respect to any stockholder rights plan existing on the date hereof or
in the event that the Company implements any other stockholder rights plan, upon
conversion of the Securities the Holders will receive, in addition to the Common
Stock issuable upon such conversion, the rights issued under such rights plan
(notwithstanding the occurrence of an event causing such rights to separate from
the Common Stock at or prior to the time of conversion); provided, a Holder who
is a holder of Common Stock (or direct or indirect interests therein) at the
time of conversion, but who is not entitled as such a holder to such rights
pursuant to the terms of any such plan, shall not be eligible to receive any
such rights hereunder. Any distribution of rights or warrants pursuant to a
stockholder rights plan complying with the requirements set forth in the
immediately preceding sentence of this paragraph shall not constitute a
distribution of rights or warrants for the purposes of the other provisions of
this Section 10.06(d).

      (e) In case the Company shall, by dividend or otherwise, distribute to all
holders of its Common Stock cash (excluding any cash that is distributed upon a
merger or consolidation to which Section 10.07 applies or as part of a
distribution referred to in Section 10.06(d)), in an aggregate amount that,
combined together with (1) the aggregate amount of all other such all-cash
distributions to all holders of its Common Stock within the twelve (12) months
preceding the date of payment of such distribution, and in respect of which no
adjustment pursuant to this Section 10.06(e) has been made, and (2) the
aggregate of any cash plus the fair market value of consideration payable in
respect of any tender offer by the Company or any subsidiary for all or any
portion of the Common Stock concluded within the twelve (12) months preceding
the date of payment of such distribution, and in respect of which no adjustment
pursuant to Section 10.06(f) has been made (such aggregate amount, the "Common
Dividend Amount"), exceeds 10% of the product of the Current Market Price on the
Record Date with respect to such distribution times the number of shares of
Common Stock outstanding on such date (the "Market Capitalization"), then, and
in each such case, immediately after the close of business on such date, the
Conversion Price shall be reduced so that the same shall equal the price
determined by multiplying the Conversion Price in effect immediately prior to
the close of business on such Record Date by a fraction (i) the numerator of
which shall be equal to the Current Market Price on the Record Date less an
amount equal to the quotient of (x) the amount by which the Common Dividend
Amount exceeds 10% of the Market Capitalization and (y) the number of shares of
Common Stock outstanding on the Record Date and (ii) the denominator of which
shall be equal to the Current Market Price on such date; provided, however, that
in the event the portion of the cash so distributed applicable to one share of
Common Stock is equal to or greater than the Current Market Price of the
<PAGE>
                                      -45-


Common Stock on the Record Date, in lieu of the foregoing adjustment, adequate
provision shall be made so that each Holder shall have the right to receive upon
conversion of a Security (or any portion thereof) the amount of cash such Holder
would have received had such bolder convened such Security (or portion thereof)
immediately prior to such Record Date. In the event that such dividend or
distribution is not so paid or made, the Conversion Price shall again be
adjusted to be the Conversion Price which would then be in effect if such
dividend or distribution had not been declared.

      (f) In case a tender offer made by the Company or any subsidiary for all
or any portion of the Common Stock shall expire and such tender offer shall
require the payment to holders of Common Stock of an aggregate consideration
that together with

            (1) the aggregate of the cash plus the fair market value of
      consideration payable in respect of any other tender offers by the Company
      or any of its subsidiaries for all or any portion of the Common Stock
      expiring within the twelve (12) months preceding the expiration of such
      tender offer and in respect of which no adjustment pursuant to this
      Section 10.06(f) has been made, and

            (2) the aggregate amount of any all-cash distributions to all
      holders of the Company's Common Stock made within twelve (12) months
      preceding the expiration of such tender offer and in respect of which no
      adjustment pursuant to Section 10.06(e) has been made,

exceeds 10% of the product of the Current Market Price as of the time of
expiration of such tender offer times the number of shares of Common Stock
outstanding at such time, then, and in each such case, immediately prior to the
opening of business on the day after the expiration of such tender offer, the
Conversion Price shall be adjusted so that the same shall equal the price
determined by multiplying the Conversion Price in effect immediately prior to
the close of business on the date of the expiration of such tender offer by a
fraction of which the numerator shall be the number of shares of Common Stock
outstanding on the date of expiration of the tender offer multiplied by the
Current Market Price of the Common Stock on the Trading Day next succeeding the
date of expiration of the tender offer and the denominator shall be the sum
of (x) the fair market value of the aggregate consideration payable for all
shares of Common Stock validly tendered and not withdrawn as of the date of
expiration of the tender offer and (y) the product of the number of shares of
Common Stock outstanding less all shares validly tendered and not withdrawn as
of the date of expiration of the tender offer and the Current Market Price of
the Common Stock on the Trading Day next succeeding the date of expiration of
the tender offer, such reduction (if any) to become effective immediately prior
to the opening of business on the day following the date of expiration of the
tender offer. In the event the Company is permanently prevented by applicable
law from effecting any such purchases or all such purchases are rescinded, the
Conversion Price shall again be adjusted to be the Conversion Price which would
then be in effect if such tender offer had not been made. If the application of
this Section 10.06(f) to any tender offer would result in an

<PAGE>
                                      -46-


increase in the Conversion Price, no adjustment shall be made for such tender
offer under this Section 10.06(f).

      (g) In case of a tender or exchange offer made by a Person other than the
Company or any subsidiary for an amount which increases such Person's ownership
of Common Stock to more than 25% of the Common Stock outstanding and involves
the payment by such Person of consideration per share of Common Stock having a
fair market value that exceeds the Current Market Price of the Common Stock on
the Trading Day next succeeding the closing date of such offer, and, as of the
closing date of such offer, the Board of Directors does not recommend rejection
of such offer, then the Conversion Price shall be reduced so that the same shall
equal the price determined by multiplying the Conversion Price in effect on the
closing date of such offer by a fraction of which the numerator shall be the
number of shares of Common Stock outstanding on the closing date of such offer
multiplied by the Current Market Price of the Common Stock on the Trading Day
next succeeding the closing date of such offer and the denominator shall be the
sum of (x) the fair market value of the aggregate consideration payable for all
shares validly tendered or exchanged and not withdrawn as of the closing date of
such offer and (y) the product of the number of shares of Common Stock
outstanding less all shares validly tendered and not withdrawn as of the closing
date of such offer and the Current Market Price of the Common Stock on the
Trading Day next succeeding the closing date of such offer, such reduction to
become effective immediately prior to the opening of business on the day
following the closing date of such offer. In the event such Person is
permanently prevented by applicable law from effecting any such purchases or all
such purchases are rescinded, the Conversion Price shall again be adjusted to be
the Conversion Price which would then be in effect if such tender or exchange
offer had not been made. Notwithstanding the foregoing, the adjustment described
in this Section 10.06(g) shall not be made if, as of the closing date of such
offer, the offering documents with respect to such offer disclose a plan or
intention to cause the Company to engage in any transaction described in Article
Five.

      (h) For purposes of this Section 10.06, the following terms have the
meanings indicated:

            (1) "Closing Price" with respect to any securities on any day shall
      mean the closing sale price regular way on such day or, in case no such
      sale takes place on such day, the average of the reported closing bid and
      asked prices, regular way, in each case on the Nasdaq National Market or
      New York Stock Exchange, as applicable, or, if such security is not listed
      or admitted to trading on such Nasdaq National Market or New York Stock
      Exchange, on the principal national security exchange or quotation system
      on which such security is quoted or listed or admitted to trading, or, if
      not quoted or listed or admitted to trading on any national securities
      exchange or quotation system, the average of the closing bid and asked
      prices of such security on the over-the-counter market on the day in
      question as reported by the National Quotation Bureau Incorporated, or a
      similar generally accepted reporting service, or if not so available, in
      such manner as furnished by any New York Stock Exchange member

<PAGE>
                                      -47-


      firm selected from time to time by the Board of Directors for that
      purpose, or a price determined in good faith by the Board of Directors,
      whose determination shall be conclusive and described in a Board
      Resolution.

            (2) "Current Market Price" shall mean the average of the Closing
      Prices per share of Common Stock for the ten (10) consecutive Trading Days
      immediately prior to the date for which a Current Market Price is
      required; provided, however, that:

                  (1) if the "ex" date (as hereinafter defined) for any event
            (other than the issuance or distribution requiring such computation)
            that requires an adjustment to the Conversion Price pursuant to
            Section 10.06(a), (b), (c), (d), (e), (f) or (g) occurs during such
            ten consecutive Trading Days then the Closing Price for each
            Trading Day prior to the "ex" date for such other event shall be
            adjusted by multiplying such Closing Price by the same fraction by
            which the Conversion Price is so required to be adjusted as a result
            of such other event,

                  (2) if the "ex" date for any event (other than the issuance or
            distribution requiring such computation) that requires an adjustment
            to the Conversion Price pursuant to Section 10.06(a), (b), (c), (d),
            (e), (f) or (g) occurs on or after the "ex" date for the issuance or
            distribution requiring such computation and prior to the day in
            question, then the Closing Price for each Trading Day on and after
            the "ex" date for such other event shall be adjusted by multiplying
            such Closing Price by the reciprocal of the fraction by which the
            Conversion Price is so required to be adjusted as a result of such
            other event, and

                  (3) if the "ex" date for the issuance or distribution
            requiring such computation is prior to the day in question, after
            taking into account any adjustment required pursuant to clause (1)
            or (2) of this proviso, the Closing Price for each Trading Day on or
            after such "ex" date shall be adjusted by adding thereto the amount
            of any cash and the fair market value of the evidences of
            indebtedness, shares of capital stock or assets being distributed
            applicable to one share of Common Stock as of the close of business
            on the day before such "ex" date.

            For purposes of any computation under Sections 10.06(f) or (g), the
      Current Market Price of the Common Stock on any date shall be deemed to be
      the average of the daily Closing Prices per share of Common Stock for such
      day and the next two succeeding Trading Days; provided, however, that if
      the "ex" date for any event (other than the tender offer requiring such
      computation) that requires an adjustment to the Conversion Price pursuant
      to Section 10.06(a), (b), (c), (d), (e), (f) and (g) occurs on or after
      the date of expiration of the tender or exchange offer requiring such

<PAGE>
                                      -48-


      computation and prior to the day in question, the Closing Price for each
      Trading Day on and after the "ex" date for such other event shall be
      adjusted by multiplying such Closing Price by the reciprocal of the
      fraction by which the Conversion Price is so required to be adjusted as a
      result of such other event.

            For purposes of this definition, the term "ex" date, (1) when used
      with respect to any issuance or distribution, means the first date on
      which the Common Stock trades regular way on the relevant exchange or in
      the relevant market from which the Closing Price was obtained without the
      right to receive such issuance or distribution, (2) when used with respect
      to any subdivision or combination of shares of Common Stock, means the
      first date on which the Common Stock trades regular way on such exchange
      or in such market after the time at which such subdivision or combination
      becomes effective, and (3) when used with respect to any tender or
      exchange offer means the first date on which the Common Stock trades
      regular way on such exchange or in such market after the Expiration Time
      of such offer.

            (3) "fair market value" shall mean the amount which a willing buyer
      would pay a willing seller in an arm's length transaction determined in
      good faith by the Board of Directors, whose determination shall be
      conclusive and described in a Board Resolution.

            (4) "Record Date" shall mean, with respect to any dividend,
      distribution or other transaction or event in which the holders of Common
      Stock have the right to receive any cash, securities or other property or
      in which the Common Stock (or other applicable security) is exchanged for
      or converted into any combination of cash, securities or other property,
      the date fixed for determination of stockholders entitled to receive such
      cash, securities or other property (whether such date is fixed by the
      Board of Directors or by statute, contract or otherwise).

            (5) "Trading Day" shall mean (x) if the applicable security is
      listed or admitted for trading on the New York Stock Exchange or another
      national security exchange, a day on which the New York Stock Exchange or
      such other national security exchange, as the case may be, is open for
      business, (y) if the applicable security is quoted on the Nasdaq National
      Market, a day on which trades may be made thereon or (z) if the applicable
      security is not so listed, admitted for trading or quoted, any day other
      than a Saturday or Sunday or a day on which banking institutions in the
      State of New York are authorized or obligated by law or executive order to
      close.

      (i) The Company may make such reductions in the Conversion Price, in
addition to those required by Sections 10.06(a), (b), (c), (d), (e), (f) and
(g), as the Board of Directors considers to be advisable to avoid or diminish
any income tax to holders of Common Stock or rights to purchase Common Stock
resulting from any dividend or distribution of stock (or rights to acquire
stock) or from any event treated as such for income tax purposes.

<PAGE>
                                      -49-


      To the extent permitted by applicable law, the Company from time to time
may reduce the Conversion Price by any amount for any period of time if the
period is at least twenty (20) days and the reduction is irrevocable during the
period. Whenever the Conversion Price is reduced pursuant to the preceding
sentence, the Company shall mail to the Holder of each Security at his last
address appearing on the register maintained by the Registrar a notice of the
reduction at least fifteen (15) days prior to the date the reduced Conversion
Price takes effect, and such notice shall state the reduced Conversion Price and
the period during which it will be in effect.

      (j) No adjustment in the Conversion Price shall be required unless such
adjustment would require an increase or decrease of at least 1% in such price;
however, any adjustment that would otherwise be required to be made shall be
carried forward and taken into account in any subsequent adjustment. All
calculations under this Article Ten shall be made by the Company and shall be
made to the nearest cent or to the nearest one hundredth of a share, as the case
may be. No adjustment need be made for a change in the par value or no par value
of the Common Stock.

      (k) Whenever the Conversion Price is adjusted as herein provided, the
Company shall promptly file with the Trustee, and any Conversion Agent other
than the Trustee, an Officers' Certificate setting forth the Conversion Price
after such adjustment and setting forth a brief statement of the facts requiring
such adjustment. Unless and until a Trust Officer of the Trustee shall have
received such Officers' Certificate, the Trustee shall not be deemed to have
knowledge of any adjustment of the Conversion Price and may assume without
inquiry that the last Conversion Price of which it has knowledge remains in
effect. Promptly after delivery of such certificate, the Company shall prepare a
notice of such adjustment of the Conversion Price setting forth the adjusted
Conversion Price and the date on which each adjustment becomes effective and
shall mail such notice of such adjustment of the Conversion Price to the Holder
of each Security at his last address appearing on the register maintained by the
Registrar, within twenty (20) days of the effective date of such adjustment.
Failure to deliver such notice shall not affect the legality or validity of any
such adjustment.

      (l) In any case in which this Section 10.06 provides that an adjustment
shall become effective immediately after a Record Date for an event, the Company
may defer until the occurrence of such event (i) issuing to the Holder of any
Security converted after such Record Date and before the occurrence of such
event the additional shares of Common Stock issuable upon such conversion by
reason of the adjustment required by such event over and above the Common Stock
issuable upon such conversion before giving effect to such adjustment and (ii)
paying to such Holder any amount in cash in lieu of any fraction pursuant to
Section 10.03.

      (m) For purposes of this Section 10.06, the number of shares of Common
Stock at any time outstanding shall not include shares held in the treasury of
the Company but shall include shares issuable in respect of scrip certificates
issued in lieu of fractions of shares of

<PAGE>
                                      -50-


Common Stock. The Company will not pay any dividend or make any distribution on
shares of Common Stock held in the treasury of the Company.

SECTION 10.07.  Effect of Reclassification, Consolidation, Merger or Sale.

            In the case of (i) any reclassification or change of the outstanding
shares of Common Stock (other than a change in par value, or from par value to
no par value, or from no par value to par value, or as a result of a subdivision
or combination), (ii) any consolidation, merger or combination of the Company
with another corporation as a result of which holders of Common Stock shall be
entitled to receive stock, securities or other property or assets (including
cash) with respect to or in exchange for such Common Stock, or (iii) any sale or
conveyance of the properties and assets of the Company as, or substantially as,
an entirety to any other corporation as a result of which holders of Common
Stock shall be entitled to receive stock, securities or other property or assets
(including cash) with respect to or in exchange for such Common Stock, then,
unless an adjustment with respect thereto shall be made pursuant to Section
10.06, the Company or the successor or purchasing corporation, as the case may
be, shall execute with the Trustee a supplemental indenture providing that the
Securities shall be convertible into the kind and amount of shares of stock and
other securities or property or assets (including cash) receivable upon such
reclassification, change, consolidation, merger, combination, sale or conveyance
by a holder of a number of shares of Common Stock issuable upon conversion of
such Securities immediately prior to such reclassification, change,
consolidation, merger, combination, sale or conveyance assuming such holder of
Common Stock did not exercise rights of election, if any, as to the kind or
amount of securities, cash or other property receivable upon such consolidation,
merger, statutory exchange, sale or conveyance. Such supplemental indenture
shall provide for adjustments which shall be as nearly equivalent as may be
practicable to the adjustments provided for in this Article Ten. If, in the case
of any such reclassification, change, consolidation, merger, combination, sale
or conveyance, the stock or other securities and assets receivable thereupon by
a holder of shares of Common Stock include shares of stock or other securities
and assets of a Person other than the successor or purchasing corporation, as
the case may be, in such reclassification, change, consolidation, merger,
combination, sale or conveyance, then such supplemental indenture shall also be
executed by such other Person and shall contain such additional provisions to
protect the interests of the Holders as the Board of Directors shall reasonably
consider necessary by reason of the foregoing.

            The Company shall cause notice of the execution of such supplemental
indenture to be mailed to each Holder of Securities, at its address appearing on
the register maintained by the Registrar, within twenty (20) days after
execution thereof. Failure to deliver such notice shall not affect the legality
or validity of such supplemental indenture.

<PAGE>
                                      -51-


SECTION 10.08. Notice of Certain Transactions.

            If:

            (1) the Company proposes to take any action that would require an
      adjustment in the conversion rate;

            (2) the Company proposes to take any action that would require a
      supplemental indenture pursuant to Section 10.07; or

            (3) there is a proposed liquidation, winding up or dissolution of
      the Company,

the Company shall mail to Holders a notice stating the proposed record date for
a dividend or distribution or the proposed effective date of a subdivision,
combination, reclassification, consolidation, merger, transfer, lease,
liquidation or dissolution. The Company shall mail the notice at least 10 days
before such date. Failure to mail the notice or any defect in it shall not
affect the validity of the transaction.

SECTION 10.09.  Company Determination Final.

            Any determination that the Board of Directors makes pursuant to this
Article is conclusive, absent manifest error.

SECTION 10.10.  Trustee's Disclaimer.

            The Trustee has no duty to determine when an adjustment under this
Article or under the terms of the Securities should be made, how it should be
made or what it should be. Such information shall be timely provided to the
Trustee in an Officers' Certificate. The Trustee has no duty to determine
whether any provisions of a supplemental indenture under Section 10.07 are
correct. The Trustee makes no representation as to the validity or value of any
securities or assets issued upon conversion of Securities. The Trustee shall not
be responsible for the Company's failure to comply with this Article. Each
Conversion Agent other than the Company shall have the same protection under
this Section 10.10 as the Trustee.


                                 ARTICLE ELEVEN

                                   [RESERVED]

<PAGE>
                                      -52-


                                 ARTICLE TWELVE

                                  SUBORDINATION


SECTION 12.01.  Securities Subordinated to Senior Indebtedness.

            The Company covenants and agrees, and each Holder of a Security, by
his acceptance thereof, likewise covenants and agrees, that the indebtedness
represented by the Securities and the payment of the principal of (and premium,
if any) and interest on each and all of the Securities is hereby expressly
subordinate and junior, to the extent and in the manner hereinafter set forth,
in right of payment to the prior payment in full of all Senior Indebtedness.

            (a) Upon any distribution of assets of the Company, upon any
dissolution, winding up, liquidation or reorganization of the Company, whether
in bankruptcy, insolvency, reorganization or receivership proceedings or upon an
assignment for the benefit of creditors or any other marshaling of the assets
and liabilities of the Company or otherwise, then the holders of all Senior
Indebtedness shall first be entitled to receive payment of the full amount due
thereon in cash or other consideration satisfactory to the holders of Senior
Indebtedness in respect of principal (and premium, if any) and interest, or
provision shall be made for such amount in cash or other consideration
satisfactory to the holders of Senior Indebtedness, before the Holders of any of
the Securities are entitled to receive any payment or distribution of any
character, whether in cash, securities or other property, on account of the
principal of (or premium, if any) or interest on the indebtedness evidenced by
the Securities.

            For purposes of this Article Twelve, the words, "cash, securities or
other property" shall not be deemed to include shares of stock of the Company as
reorganized or readjusted, or securities of the Company or any other corporation
provided for by a plan of reorganization or readjustment, the payment of which
is subordinated at least to the extent provided in this Article Twelve with
respect to the Securities to the payment of all Senior Indebtedness which may at
the time be outstanding; provided that (i) the Senior Indebtedness is assumed by
the new corporation, if any, resulting from any reorganization or readjustment,
and (ii) the rights of the holders of Senior Indebtedness (other than leases
which are not assumed by the Company or the new corporation, as the case may be)
are not, without the consent of such holders, altered by such reorganization or
readjustment. The consolidation of the Company with, or the merger of the
Company into, another Person or the liquidation or dissolution of the Company
following the conveyance or transfer of its property as an entirety, or
substantially as an entirety, to another Person upon the terms and conditions
provided for in Article Five shall not be deemed a dissolution, winding-up,
liquidation or reorganization for the purposes of this Section 12.01(a) if such
other Person shall, as a part of such consolidation, merger, conveyance or
transfer, comply with the conditions stated in Article Five.

            (b) No payment shall be made by the Company with respect to the
principal of, premium, if any, or interest on the Securities or to acquire any
of the Securities, if (i) any default in payment of the principal of or premium,
if any, or interest on, rent under, or any other payment obligation under any
Senior Indebtedness occurs and is continuing (a "Payment Default") beyond any
applicable

<PAGE>
                                      -53-


grace period with respect thereto, unless and until all such payments due in
respect of such Senior Indebtedness have been paid in full in cash or other
consideration satisfactory to holders of Senior Indebtedness or such default
shall have been cured or waived or shall have ceased to exist, (ii) any event of
default, other than a Payment Default, with respect to any Designated Senior
Indebtedness occurs and is continuing permitting the holders of such Designated
Senior Indebtedness (or a trustee or other representative on behalf of the
holders thereof) to declare such Designated Senior Indebtedness due and payable
prior to the date on which it would otherwise have become due and payable, and
the Trustee receives notice thereof from the Company or by any holders of such
Designated Senior Indebtedness (or a trustee or other representative on behalf
of the holders thereof) (the "Payment Blockage Notice"), for a period (the
"Payment Blockage Period") ending on the earlier of the date on which such event
of default shall have been cured or waived or shall have ceased to exist or 179
days after receipt of the Payment Blockage Notice, or (iii) any judicial
proceeding shall be pending with respect to any such default in payment or event
of default; provided, further, any number of additional Payment Blockage Periods
may be commenced during an existing Payment Blockage Period; provided, however,
that no such additional Payment Blockage Period shall extend beyond the initial
Payment Blockage Period. Notwithstanding anything in the subordination
provisions of this Indenture or the Securities to the contrary, (x) in no event
will a Payment Blockage Period extend beyond 179 days from the date of the
Payment Blockage Notice in respect thereof was given and (y) there shall be a
period of at least 181 consecutive days in each 360-day period when no Payment
Blockage Period is in effect. No nonpayment default that existed or was
continuing on the date of delivery of any Payment Blockage Notice to the Trustee
shall be the basis for a subsequent payment blockage notice.

            (c) If the maturity of the Securities is accelerated, no payment may
be made on the Securities until all amounts due or to become due on Senior
Indebtedness have been paid in full in cash or other consideration satisfactory
to holders of Senior Indebtedness or until such acceleration has been cured or
waived.

            (d) In the event that, notwithstanding the foregoing provisions of
Sections 12.01(a), (b) and (c), any payment on account of principal of or
interest on the Securities shall be made by or on behalf of the Company and
received by the Trustee, by any Holder or by any Paying Agent (or, if the
Company is acting as its own Paying Agent, money for any such payment shall be
segregated and held in trust), at a time when such payment is not permitted by
any of such provisions, then, unless and until all Senior Indebtedness (or
Designated Senior Indebtedness, in the case of Section 12.01(b)) is paid in full
in cash or other consideration satisfactory to the holders thereof, or such
payment is otherwise permitted to be made by the provisions of each of Sections
12.01(a), 12.01(b) and 12.01(c) (subject, in each case, to the provisions of
Section 12.07), such payment on account of principal of or interest on the
Securities shall be held in trust for the benefit of, and shall be immediately
paid over to, the holders of Senior Indebtedness (or Designated Senior
Indebtedness, in the case of Section 12.01(b)) or their representative or
representatives or the trustee or trustees under any indenture under which any
instruments evidencing any of the Senior Indebtedness (or Designated Senior
Indebtedness, in the case of Section 12.01(b)) may have been issued, as their
interests may appear.

<PAGE>
                                      -54-


            Regardless of anything to the contrary herein, nothing shall prevent
(A) any payment by the Company or the Trustee to Holders of amounts in
connection with a redemption of Securities if (i) notice of such redemption has
been given pursuant to Section 3.01 prior to the receipt by the Trustee of a
Payment Blockage Notice, and (ii) such notice of redemption is given not earlier
than 75 days before the Redemption Date, or (B) any payment by the Trustee to
the Holders of amounts deposited with it pursuant to Section 8.01.

SECTION 12.02.  Subrogation.

            Subject to the payment in full of all Senior Indebtedness to which
the indebtedness evidenced by the Securities is in the circumstances
subordinated as provided in Section 12.01, the Holders of the Securities
(together with the holders of any other indebtedness of the Company which is
subordinate in right of payment to the payment in full of all Senior
Indebtedness, which is not subordinate in right of payment to the Securities and
which by its terms grants such right of subrogation to the holders thereof)
shall be subrogated to the rights of the holders of such Senior Indebtedness to
receive payments or distributions of cash, property or securities of the Company
applicable to such Senior Indebtedness until all amounts owing on the Securities
shall be paid in full, and, as between the Company, its creditors other than
holders of such Senior Indebtedness, and the Holders of the Securities, no such
payment or distribution made to the holders of Senior Indebtedness by virtue of
this Article which otherwise would have been made to the Holders of the
Securities shall be deemed to be a payment by the Company on account of such
Senior Indebtedness, it being understood that the provisions of this Article are
and are intended solely for the purpose of defining the relative rights of the
Holders of the Securities, on the one hand, and the holders of Senior
Indebtedness, on the other hand.

SECTION 12.03.  Obligation of Company Unconditional.

            Nothing contained in this Article or elsewhere in this Indenture or
in the Securities is intended to or shall impair, as between the Company, its
creditors other than the holders of Senior Indebtedness, and the Holders of the
Securities, the obligation of the Company, which is absolute and unconditional,
to pay to the Holders of the Securities the principal of (and premium, if any)
and interest on the Securities as and when the same shall become due and payable
in accordance with their terms, or is intended to or shall affect the relative
rights of the Holders of the Securities and creditors of the Company other than
the holders of Senior Indebtedness, nor shall anything herein or therein prevent
the Trustee or the Holder of any Security from exercising all remedies otherwise
permitted by applicable law upon default under this Indenture, subject to the
rights, if any, under this Article of the holders of Senior Indebtedness in
respect of cash, property or securities of the Company received upon the
exercise of any such remedy.

SECTION 12.04.  Modification of Terms of Senior Indebtedness.

            Any renewal or extension of the time of payment of any Senior
Indebtedness or the exercise by the holders of Senior Indebtedness of any of
their rights under any instrument creating or evidencing Senior Indebtedness,
including without limitation the waiver of default thereunder, may be made or
done all without notice to or assent from the Holders of the Securities or the
Trustee.

<PAGE>
                                      -55-


            No compromise, alteration, amendment, modification, extension,
renewal or other change of, or waiver, consent or other action in respect of,
any liability or obligation under or in respect of, or of any of the terms,
covenants or conditions of any indenture or other instrument under which any
Senior Indebtedness is outstanding or of such Senior Indebtedness, whether or
not such release is in accordance with the provisions of any applicable
document, shall in any way alter or affect any of the provisions of this Article
or of the Securities relating to the subordination thereof.

SECTION 12.05.  [Reserved]

SECTION 12.06.  Effectuation of Subordination by Trustee.

            Each Holder of Securities, by his acceptance thereof, authorizes and
directs the Trustee in his or her behalf to take such action as may be necessary
or appropriate to effectuate the subordination provided in this Article and
appoints the Trustee his or attorney-in-fact for any and all such purposes.

            Upon any payment or distribution of assets of the Company referred
to in this Article, the Trustee and the Holders of the Securities shall be
entitled to rely upon any order or decree made by any court of competent
jurisdiction in which any such dissolution, winding up, liquidation or
reorganization proceeding affecting the affairs of the Company is pending or
upon a certificate of the trustee in bankruptcy, receiver, assignee for the
benefit of creditors, liquidating trustee or agent or other Person making any
payment or distribution, delivered to the Trustee or to the Holders of the
Securities, for the purpose of ascertaining the Persons entitled to participate
in such payment or distribution, and as to other facts pertinent to the right of
such Persons under this Article, and if such evidence is not furnished, the
Trustee may defer any payment to such Persons pending judicial determination as
to the right of such Persons to receive such payment.

SECTION 12.07.  Knowledge of Trustee.

            Notwithstanding the provisions of this Article or any other
provisions of this Indenture, the Trustee shall not be charged with knowledge of
the existence of any Senior Indebtedness, of any default in payment of
principal, premium (if any) or interest on any Senior Indebtedness, or of any
facts which would prohibit the making of any payment of moneys to or by the
Trustee, or the taking of any other action by the Trustee, unless and until a
Trust Officer of the Trustee having responsibility for the administration of the
trust established by this Indenture shall have received written notice thereof
from the Company, any Holder of Securities, any Paying or Conversion Agent of
the Company or the holder or representative of any class of Senior Indebtedness,
and, prior to the receipt of any such written notice, the Trustee shall be
entitled in all respects to assume that no such default or facts exist;
provided, however, that unless on the third Business Day prior to the date upon
which by the terms hereof any such moneys may become payable for any purpose the
Trustee shall have received the notice provided for in this Section 12.07, then,
anything herein contained to the contrary notwithstanding, the Trustee shall
have full power and authority to receive such moneys and apply the same to the
purpose for which they were received, and shall not be affected by any notice to
the contrary which may be received by it on or after such date.

<PAGE>
                                      -56-


SECTION 12.08.  Trustee's Relation to Senior Indebtedness.

            The Trustee shall be entitled to all the rights set forth in this
Article with respect to any Senior Indebtedness at the time held by it, to the
same extent as any other holder of Senior Indebtedness and nothing in this
Indenture shall deprive the Trustee of any of its rights as such holder.

            Nothing in this Article shall apply to claims of or payments to the
Trustee under or pursuant to Section 7.07.

            With respect to the holders of Senior Indebtedness, the Trustee
undertakes to perform or to observe only such of its covenants and obligations
as are specifically set forth in this Article, and no implied covenants or
obligations with respect to the holders of Senior Indebtedness shall be read
into this Indenture against the Trustee. The Trustee shall not be deemed to owe
any fiduciary duty to the holders of Senior Indebtedness and the Trustee shall
not be liable to any holder of Senior Indebtedness if it shall pay over or
deliver to Holders, the Company or any other Person moneys or assets to which
any holder of Senior Indebtedness shall be entitled by virtue of this Article or
otherwise.

SECTION 12.09.  Rights of Holders of Senior Indebtedness Not
                Impaired.

            No right of any present or future holder of any Senior Indebtedness
to enforce the subordination herein shall at any time or in any way be
prejudiced or impaired by any act or failure to act on the part of the Company
or by any noncompliance by the Company with the terms, provisions and covenants
of this Indenture, regardless of any knowledge thereof any such holder may have
or be otherwise charged with.

SECTION 12.10.  Certain Conversions Not Deemed Payment.

            For the purposes of Article Ten only, (1) the issuance and delivery
of junior securities upon conversion of Securities in accordance with Article
Ten shall not be deemed to constitute a payment or distribution on account of
the principal of, premium, if any, or interest on Securities or on account of
the purchase or other acquisition of Securities, and (2) the payment, issuance
or delivery of cash (except in satisfaction of fractional shares pursuant to
Section 10.03), property or securities (other than junior securities) upon
conversion of a Security shall be deemed to constitute payment on account of the
principal of, premium, if any, or interest on such Security. For the purposes of
this Section 12.10, the term "junior securities" means (a) shares of any stock
of any class of the Company or (b) securities of the Company that are
subordinated in right of payment to all Senior Indebtedness to substantially the
same extent as, or to a greater extent than, the Securities are so subordinated
as provided in this Article. Nothing contained in this Article Twelve or
elsewhere in this Indenture or in the Securities is intended to or shall impair,
as among the Company, its creditors (other than holders of Senior Indebtedness)
and the Holders, the right, which is absolute and unconditional, of the Holder
of any Security to convert such note in accordance with Article Ten.

<PAGE>
                                      -57-


                                ARTICLE THIRTEEN

                                  MISCELLANEOUS


SECTION 13.01.  Trust Indenture Act Controls.

            If any provision of this Indenture limits, qualifies or conflicts
with another provision which is required to be included in this Indenture by the
TIA, the required provision shall control.

SECTION 13.02.  Notices.

            Any notice or communication by the Company or the Trustee to the
other is duly given if in writing and delivered in person, mailed by first-class
mail or by express delivery to the other's address stated in this Section 13.02.
The Company or the Trustee by notice to the other may designate additional or
different addresses for subsequent notices or communications.

            Any notice or communication to a Holder shall be mailed by
first-class mail to its address shown on the register kept by the Registrar.
Failure to mail a notice or communication to a Holder or any defect in it shall
not affect its sufficiency with respect to other Holders.

            If a notice or communication is mailed in the manner provided above,
it is duly given, whether or not the addressee receives it.

            If the Company mails a notice or communication to Holders, it shall
mail a copy to the Trustee and each Agent at the same time.

            All notices or communications shall be in writing.

            The Company's address is:

                   Alexion Pharmaceuticals, Inc.
                   25 Science Park
                   New Haven, Connecticut 06511
                   Attention: President

            The Trustee's address is:

                   The Chase Manhattan Bank
                   450 West 33rd Street, 15th Floor
                   New York, NY 10001
                   Attention: Capital Markets Fiduciary Services

<PAGE>
                                      -58-


SECTION 13.03.  Communication by Holders with Other Holders.

            Holders may communicate pursuant to TIA ss. 312(b) with other
Holders with respect to their rights under this Indenture or the Securities. The
Company, the Trustee, the Registrar and anyone else shall have the protection of
TIA ss. 312(c).

SECTION 13.04.  Certificate and Opinion as to Conditions Precedent.

            Upon any request or application by the Company to the Trustee to
take any action under this Indenture the Company shall furnish to the Trustee:

            (1) an Officers' Certificate stating that, in the opinion of the
      signers, all conditions precedent, if any, provided for in this Indenture
      relating to the proposed action have been complied with; and

            (2) an Opinion of Counsel stating that, in the opinion of such
      counsel, all such conditions precedent have been complied with.

            Each signer of an Officers' Certificate or an Opinion of Counsel may
(if so stated) rely, effectively, upon an Opinion of Counsel as to legal matters
and an Officers' Certificate as to factual matters if such signer reasonably and
in good faith believes in the accuracy of the document relied upon.

SECTION 13.05.  Statements Required in Certificate or Opinion.

            Each Officers' Certificate or Opinion of Counsel with respect to
compliance with a condition or covenant provided for in this Indenture shall
include:

            (1) a statement that the Person making such certificate or opinion
      has read such covenant or condition;

            (2) a brief statement as to the nature and scope of the examination
      or investigation upon which the statements or opinions contained in such
      certificate or opinion are based;

            (3) a statement that, in the opinion of such Person, he or she has
      made such examination or investigation as is necessary to enable him or
      her to express an informed opinion as to whether or not such covenant or
      condition has been complied with; and

            (4) a statement as to whether or not, in the opinion of such Person,
      such condition or covenant has been complied with.

<PAGE>
                                      -59-


SECTION 13.06.  Rules by Trustee and Agents.

            The Trustee may make reasonable rules for action by or at a meeting
of Holders. The Registrar, Paying Agent or Conversion Agent may make reasonable
rules and set reasonable requirements for their respective functions.

SECTION 13.07.  Legal Holidays.

            A "Legal Holiday" is a Saturday, a Sunday or a day on which banking
institutions are not required to be open in The City of New York, in the State
of New York or in the city in which the Trustee administers its corporate trust
business. If a payment date is a Legal Holiday at a place of payment, payment
may be made at that place on the next succeeding day that is not a Legal
Holiday, and no interest shall accrue on that payment for the intervening
period.

            A "Business Day" is a day other than a Legal Holiday.

SECTION 13.08.  No Recourse Against Others.

            All liability described in the Securities of any director, officer,
employee or stockholder, as such, of the Company is waived and released.

SECTION 13.09.  Duplicate Originals.

            The parties may sign any number of copies of this Indenture. Each
signed copy shall be an original, but all of them together represent the same
agreement.

SECTION 13.10.  Governing Law.

            The laws of the State of New York, without regard to principles of
conflicts of law, shall govern this Indenture and the Securities.

SECTION 13.11.  No Adverse Interpretation of Other Agreements.

            This Indenture may not be used to interpret another indenture, loan
or debt agreement of the Company or a subsidiary. Any such indenture, loan or
debt agreement may not be used to interpret this Indenture.

SECTION 13.12.  Successors.

            All agreements of the Company in this Indenture and the Securities
shall bind its successors. All agreements of the Trustee in this Indenture shall
bind its successors.

<PAGE>
                                      -60-


SECTION 13.13.  Separability.

            In case any provision in this Indenture or in the Securities shall
be invalid, illegal or unenforceable, the validity, legality and enforceability
of the remaining provisions shall not in any way be affected or impaired thereby
and a Holder shall have no claim therefor against any party hereto.

SECTION 13.14.  Table of Contents, Headings, etc.

            The Table of Contents, Cross-Reference Table and headings of the
Articles and Sections of this Indenture have been inserted for convenience of
reference only, are not to be considered a part hereof and shall in no way
modify or restrict any of the terms or provisions hereof.

<PAGE>
                                       S-1


                                   SIGNATURES

            IN WITNESS WHEREOF, the parties hereto have caused this Indenture to
be duly executed as of the date first above written.


                                        ALEXION PHARMACEUTICALS, INC.

                                        By: /s/ David Keiser
                                            -----------------------------------
                                            Name:
                                            Title:


                                        THE CHASE MANHATTAN BANK, as
                                          Trustee

                                        By: /s/ Kathleen Perry
                                            -----------------------------------
                                            Name: Kathleen Perry
                                            Title: Vice President

<PAGE>

                                                                       EXHIBIT A
REGISTERED                     [Face of Security]
NUMBER                                                                   DOLLARS


                          ALEXION PHARMACEUTICALS, INC.


                  5 3/4% CONVERTIBLE SUBORDINATED NOTE DUE 2007

            ALEXION PHARMACEUTICALS, INC., a Delaware corporation (herein called
the "Company"), for value received, hereby promises to pay to
or registered assigns, the principal sum of           Dollars on March 15, 2007,
and to pay interest thereon as provided on the reverse hereof on the principal
sum, until the principal hereof and any unpaid and accrued interest is paid or
duly provided for. The right to payment of principal, premium, if any, and
interest is subordinated to the rights of Senior Indebtedness as set forth in
the Indenture referred to on the reverse side hereof.

            Interest Payment Dates: March 15 and September 15, with the first
payment to be made on September 15, 2000.

            Record Dates: March 1 and September 1.

<PAGE>

            IN WITNESS WHEREOF, ALEXION PHARMACEUTICALS, INC. has caused this
instrument to be duly signed.

                                        ALEXION PHARMACEUTICALS, INC.

                                        By:
                                            -----------------------------------
                                            Name:
                                            Title:


                                        By:
                                            -----------------------------------
                                            Name:
                                            Title:


Dated:

TRUSTEE'S CERTIFICATE OF
   AUTHENTICATION

This is one of the Securities referred to in the within-mentioned Indenture.

THE CHASE MANHATTAN BANK, as Trustee


By:
    ---------------------------------
            Authorized Officer

                                      A-2
<PAGE>

                              [REVERSE OF SECURITY]

                          ALEXION PHARMACEUTICALS, INC.

                  5 3/4% CONVERTIBLE SUBORDINATED NOTE DUE 2007

            1. Interest. Alexion Pharmaceuticals, Inc., a Delaware corporation
(the "Company"), promises to pay interest on the principal amount of this
Security at the rate per annum shown above. The Company will pay interest
semi-annually in arrears on March 15 and September 15 of each year, with the
first payment to be made on September 15, 2000. Interest on the Securities will
accrue on the principal amount from the most recent date to which interest has
been paid or duly provided for or, if no interest has been paid, from March 8,
2000. Interest will be computed on the basis of a 360-day year of twelve 30-day
months.

            2. Maturity. The Securities will mature on March 15, 2007 unless
earlier converted, redeemed or repurchased pursuant to the terms hereof and the
Indenture.

            3. Method of Payment. The Company will pay interest on the
Securities (except defaulted interest) to the Persons who are registered Holders
of Securities at the close of business on the record date set forth on the face
of this Security next preceding the applicable interest payment date except that
(i) interest payable upon redemption or repurchase, unless the date of
redemption or repurchase is an interest payment date, will be payable to the
Person to whom the principal is payable and (ii) in the case of any Security or
portion of any Security that is converted into Common Stock during the period
from, but excluding, a record date for any interest payment date to, but
excluding, that interest payment date either (A) if the Security, or portion of
the Security, has been called for redemption on a redemption date that occurs
during that period, or is to be repurchased on a Repurchase Date that occurs
during that period, the Company will not be required to pay interest on that
interest payment date in respect of any Security, or portion of any Security,
that is so redeemed or repurchased; or (B) if otherwise, any Security or portion
of any Security that is not called for redemption but is submitted for
conversion during that period must be accompanied by funds equal to the interest
payable on that interest payment date on the principal amount so converted.
Holders must surrender Securities to a Paying Agent to collect the principal
payments. The Company will pay the principal, premium, if any, and interest in
money of the United States that at the time of payment is legal tender.
Principal and interest may, at the Company's option, be paid either (i) by check
mailed to the address of the Person entitled to the interest as it appears in
the register kept by the Registrar (provided (a) payments to the Depository will
be made by wire transfer of immediately available funds to the account of the
Depository or its nominee and (b) a Holder with an aggregate principal amount of
Securities in excess of $10 million will, at the written election of the Holder,
filed on or before the relevant record date with the Trustee, be paid by wire
transfer in immediately available funds); or (ii) by transfer to an account
maintained by that Person located in the U.S.

            4. Paying Agent, Registrar, Conversion Agent. Initially, The Chase
Manhattan Bank (the "Trustee") will act as Paying Agent, Registrar and
Conversion Agent. The Company may change any Paying Agent, Registrar or
Conversion Agent without notice. The Company may act in any such capacity.

                                      A-3
<PAGE>

            5. Indenture. The Company issued the Securities under an Indenture
dated as of March 8, 2000 (the "Indenture") between the Company and the Trustee.
The terms of the Securities include those stated in the Indenture and those made
part of the Indenture by reference to the Trust Indenture Act of 1939 (15 U.S.
Code ss.ss. 77aaa-77bbbb) (the "Act") as in effect on the date of the Indenture.
The Securities are subject to all such terms, and Holders are referred to the
Indenture and the Act for a statement of such terms. The Securities are general
unsecured subordinated obligations of the Company limited to a maximum of
$120,000,000 aggregate principal amount (plus such additional amount (up to an
aggregate of $130,000,000) purchased by the Initial Purchasers pursuant to the
option described in Section 2.02), except as otherwise provided in the Indenture
(except for Securities issued in substitution for destroyed, mutilated, lost or
stolen Securities). Terms used herein which are defined in the Indenture have
the meanings assigned to them in the Indenture.

            6. Optional Redemption by the Company. At any time on or after March
20, 2003, the Company may redeem the Securities on at least 30 days' notice as a
whole or, from time to time, in part at the following prices, expressed as a
percentage of the principal amount, together with accrued interest to, but
excluding, the date fixed for redemption:

                                                                    Redemption
Period                                                                 Price
------                                                              ----------

Beginning March 20, 2003 and ending on March 14, 2004 ...........    103.286%
Beginning March 15, 2004 and ending on March 14, 2005 ...........    102.464%
Beginning March 15. 2005 and ending on March 14. 2006 ...........    101.643%
Beginning March 15. 2006 and ending on March 14, 2007 ...........    100.822%

and 100% on March 15, 2007. My accrued interest becoming due on the date fixed
for redemption will be payable to the holders of record on the relevant record
date of the Securities being redeemed.

            7. Notice of Redemption. Notice of redemption pursuant to paragraph
6 will be mailed at least 30 days before the redemption date to each Holder of
Securities to be redeemed at its registered address. Securities in denominations
larger than $1,000 principal amount may be redeemed in part but only in whole
multiples of $1,000 principal amount. On and after the redemption date interest
ceases to accrue on Securities or portions of them called for redemption.

            8. Repurchase at Option of Holder. Pursuant to Section 3.07 of the
Indenture within 15 days after a Repurchase Event occurs, the Company is
required to give notice of the Repurchase Event to the Holders. Each Holder has
the right, at its option, to require the Company to repurchase all or any
portion of the Securities 40 days after the notice of repurchase event is
mailed. The Repurchase Price will be 105% of the principal amount of the
Securities submitted for repurchase, plus accrued and unpaid interest to, but
excluding, the Repurchase Date. If a Repurchase Date is an interest payment
date, then the interest payable on that date will be paid to the holder of
record on the relevant record date. Subject to the conditions of Section 3.07 of
the Indenture, the Company, at its option, instead of paying the Repurchase
Price in cash, may pay the Repurchase Price in Common Stock, valued at 95% of
the average of the Closing Prices for the five Trading Days immediately before
and including the third Trading Day preceding the Repurchase Date.

            9. Conversion. A Holder of a Security may convert the principal of
such Security into Common Stock at any time after the date of original issuance
of the Security to the close of

                                      A-4
<PAGE>

business on the business day prior to March 15, 2007, or (x) if the Security
is called for redemption by the Company, the Holder may convert it at any
time before the close of business on the date that is one business day before
the date fixed for such redemption, or (y) if the Security is to be
repurchased by the Company pursuant to paragraph 8 hereof, the Holder may
convert it at any time before the close of business on the date that is one
business day before the date fixed for such repurchase. The initial
Conversion Price is $106.425 per share of Common Stock, subject to adjustment
in certain circumstances as set forth in Section 10.06 of the Indenture. To
determine the number of shares issuable upon conversion of a Security, divide
the principal amount to be converted by the Conversion Price in effect on the
conversion date and round the result to the nearest 1/100th share. The
Company is not required to issue fractional shares of Common Stock upon
conversion and, instead, will pay a cash amount as provided in Section 10.03
of the Indenture. Except as provided in Article Ten of the Indenture, no
payment or adjustment for the principal of, premium, if any, interest on or
liquidated damages with respect to, the Securities or for dividends on any
Common Stock will be made. If a Holder surrenders a Security for conversion
between the record date for the payment of interest and the next interest
payment date, such Security, when surrendered for conversion, must be
accompanied by payment of an amount equal to the interest thereon which the
registered Holder on such record date is to receive. A Security which the
Holder has elected to be repurchased may be converted only if the Holder
withdraws its election to have such Security repurchased in accordance with
the terms of the Indenture before the close of business on the business day
prior to the Repurchase Date.

            To convert a Security a Holder must (1) complete and sign the
Conversion Notice, with appropriate signature guarantee, on the back of the
Security, (2) surrender the Security to a Conversion Agent, (3) furnish
appropriate endorsements and transfer documents if required by the Registrar or
Conversion Agent, (4) pay the amount of interest, if any, the Holder may be paid
as provided in the last sentence of the above paragraph and (5) pay any transfer
or similar tax if required. A Holder may convert a portion of a Security if the
portion is $1,000 principal amount or a whole multiple of $ 1,000 principal
amount.

            Any shares issued upon conversion of a Security shall bear the
Private Placement Legend until after the second anniversary of the later of the
issue date for the Securities and the last date on which the Company or any
Affiliate of the Company was the owner of such shares or the Security (or any
predecessor security) from which such shares were converted (or such shorter
period of time as permitted by Rule 144(k) under the Securities Act or any
successor provision thereunder) (or such longer period of time as may be
required under the Securities Act or applicable state securities laws as set
forth in the Opinion of Counsel delivered to the Conversion Agent, unless
otherwise agreed by the Company and the Holder thereof).

            10. Subordination. The Securities are subordinated in right of
payment, in the manner and to the extent set forth in the Indenture, to the
prior payment in full of all Senior Indebtedness. Each Holder by accepting a
Security agrees to such subordination and authorizes the Trustee to give it
effect.

            11. Denominations, Transfer, Exchange. The Securities are in
registered form without coupons in denominations of $1,000 principal amount and
whole multiples of $1,000 principal amount. The transfer of Securities may be
registered and Securities may be exchanged as provided in the Indenture. The
Registrar may require a Holder, among other things, to furnish appropriate
endorsements and transfer documents. No service charge shall be made for any
such registration

                                      A-5
<PAGE>

of transfer or exchange, but the Company may require payment of a sum sufficient
to cover any tax or other governmental charge payable in connection therewith.
The Registrar need not exchange or register the transfer of any Security
selected for redemption in whole or in part. Also, it need not exchange or
register the transfer of any Securities for a period of 15 days before the
mailing of a notice of redemption of the Securities selected to be redeemed.

            12. Persons Deemed Owners. The registered Holder of a Security may
be treated as the owner of such Security for all purposes.

            13. Merger or Consolidation. The Company shall not consolidate with,
or merge into, or transfer or lease all or substantially all of its assets to,
any Person unless, among other things, the Person is organized under the laws of
the United States, any State thereof or the District of Columbia and such Person
assumes by supplemental indenture all the obligations of the Company under the
Securities, the Indenture and the Registration Rights Agreement and after giving
effect to the transaction no Default or Event of Default exists.

            Notwithstanding the foregoing, any subsidiary of the Company may
consolidate with, merge into or transfer all or part of its properties and
assets to the Company or any other subsidiary or subsidiaries of the Company.

            14. Amendments, Supplements and Waivers. Subject to certain
exceptions, the Indenture or the Securities may be amended or supplemented with
the consent of the Holders of at least a majority in aggregate principal amount
of the Securities then outstanding, and any existing Default or Event of Default
may be waived with the consent of the Holders of a majority in aggregate
principal amount of the Securities then outstanding. Without notice to or the
consent of any Holder, the Indenture or the Securities may be amended or
supplemented to cure any ambiguity, omission, defect or inconsistency, to
provide for uncertificated Securities in addition to certificated Securities, to
comply with Sections 5.01 and 10.07 of the Indenture or to make any change that
does not adversely affect the rights of any Holder.

            15. Defaults and Remedies. An Event of Default includes the
occurrence of any or the following: default in payment of the principal of or
any premium on the Securities; default for 30 days in payment of interest;
failure by the Company for 90 days after notice to it to comply with any of its
other agreements in the Indenture or the Securities; and certain events of
bankruptcy or insolvency. If any Event of Default occurs and is continuing, the
Trustee or the Holders of at least 25% in aggregate principal amount of the
Securities then outstanding may declare all the Securities to be due and
payable. Holders may not enforce the Indenture or the Securities except as
provided in the Indenture. The Trustee may require indemnity satisfactory to it
before it enforces the Indenture or the Securities. Subject to certain
limitations, Holders of a majority in principal amount of the Securities then
outstanding may direct the Trustee in its exercise of any trust or power. The
Trustee may withhold from Holders notice of any continuing Default or Event of
Default (except a Default or Event of Default in payment of principal or
interest) if it determines that withholding notice is in their interests. The
Company must furnish an annual compliance certificate to the Trustee.

            16. Registration Rights. The Holders are entitled to shelf
registration rights as set forth in the Registration Rights Agreement. The
Holders shall be entitled to receive liquidated damages in certain
circumstances, all as set forth in the Registration Rights Agreement.

                                      A-6
<PAGE>

            17. Trustee Dealings with Company. The Trustee under the Indenture,
or any banking institution serving as successor Trustee thereunder, in its
individual or any other capacity, may make loans to, accept deposits from, and
perform services for the Company or its Affiliates, and may otherwise deal with
the Company or its Affiliates, as if it were not Trustee.

            18. No Recourse Against Others. No past, present or future director,
officer, employee or stockholder, as such, of the Company shall have any
liability for any obligations of the Company under the Securities or the
Indenture or for any claim based on, in respect of or by reason of such
obligations or their creation. Each Holder by accepting a Security waives and
releases all such liability. The waiver and release are part of the
consideration for the issue of the Securities.

            19. Authentication. This Security shall not be valid until
authenticated by the manual signature of the Trustee or an authenticating agent.

            20. Abbreviations. Customary abbreviations may be used in the name
of a Holder or an assignee, such as: TEN COM ( tenants in common), TEN ENT (=
tenants by the entirety), JT TEN (= joint tenants with right of survivorship and
not as tenants in common), CUST (= Custodian), and U/G/M/A (Uniform Gifts to
Minors Act).

            THE COMPANY WILL FURNISH TO ANY SECURITYHOLDER UPON WRITTEN REQUEST
AND WITHOUT CHARGE A COPY OF THE INDENTURE. REQUESTS MAY BE MADE TO:

            ALEXION PHARMACEUTICALS, INC.
            25 SCIENCE PARK
            NEW HAVEN, CONNECTICUT 06511
            ATTENTION: PRESIDENT


                                       A-7
<PAGE>

                              [FORM OF ASSIGNMENT]

I or we assign to

PLEASE INSERT SOCIAL SECURITY OR
OTHER IDENTIFYING NUMBER


___________________________________________

________________________________________________________________________________
(please print or type name and address)

________________________________________________________________________________

________________________________________________________________________________
the within Security and all rights thereunder, and hereby irrevocably
constitutes and appoints

________________________________________________________________________________
attorney to transfer the Security on the books of the Company with full power of
substitution in the premises.

Dated:_______________________________   ________________________________________
                                        NOTICE: The signature on this assignment
                                        must correspond with the name as it
                                        appears upon the face of the within
                                        Security in every particular without
                                        alteration or enlargement or any change
                                        whatsoever and be guaranteed by the
                                        endorser's bank or broker.

Signature Guarantee: ___________________________________________________________

            (Signatures must be guaranteed by an "eligible guarantor
institution" meeting the requirements of the Registrar, which requirements
include membership or participation in the Security Transfer Agent Medallion
Program ("STAMP") or such other "signature guarantee program" as may be
determined by the Registrar in addition to, or in substitution for, STAMP, all
in accordance with the Securities Exchange Act of 1934, as amended.)

            In connection with any transfer of this Security occurring prior to
the date which is the earlier of (i) the date of the declaration by the
Commission of the effectiveness of a registration statement under the Securities
Act of 1933, as amended (the "Securities Act") covering resales of this Security
(which effectiveness shall have been suspended or terminated at the date of the
transfer) and (ii) March 7, 2002 the undersigned confirms that it has not
utilized any general solicitation or general advertising in connection with
transfer:


                                      A-8
<PAGE>

                                  [Check One]

(1) ___     to the Company or a subsidiary thereof; or

(2) ___     pursuant to and in compliance with Rule 144A under the Securities
            Act of 1933, as amended; or

(3) ___     to an institutional "accredited investor" (as defined in Rule
            50l(a)(1), (2), (3) or (7) under the Securities Act of 1933, as
            amended) that has furnished to the Trustee a signed letter
            containing certain representations and agreements (the form of which
            letter can be obtained from the Trustee); or

(4) ___     outside the United States to a "foreign purchaser" in compliance
            with Rule 904 of Regulation S under the Securities Act of 1933, as
            amended; or

(5) ___     pursuant to the exemption from registration provided by Rule 144
            under the Securities Act of 1933, as amended; or

(6) ___     pursuant to an effective registration statement under the Securities
            Act of 1933, as amended; or

(7) ___     pursuant to another available exemption from the registration
            statement requirements of the Securities Act of 1933, as amended.

and unless the box below is checked, the undersigned confirms that such Security
is not being transferred to an "affiliate" of the Company as defined in Rule 144
under the Securities Act of 1933, as amended (an "Affiliate"):

            |_| The transferee is an Affiliate of the Company.

(If the Security is transferred to an Affiliate, the restrictive legend must
remain on the Security for two years following the date of the transfer).

            Unless one of the items is checked, the Trustee will refuse to
register any of the Securities evidenced by this certificate in the name of any
Person other than the registered Holder thereof; provided, however, that if item
(3),(4),(5) or (7) is checked, the Company or the Trustee may require, prior to
registering any such transfer of the Securities, in their sole discretion, such
written legal opinions, certifications (including an investment letter in the
case of box (3) or (4)) and other information as the Trustee or the Company have
reasonably requested to confirm that such transfer is being made pursuant to an
exemption from, or in a transaction not subject to, the registration
requirements of the Securities Act of 1933, as amended.

            If none of the foregoing items are checked, the Trustee or Registrar
shall not be obligated to register this Security in the name of any Person other
than the Holder hereof unless and until the conditions to any such transfer of
registration set forth herein and in Section 2.16 of the Indenture shall have
been satisfied.


                                      A-9
<PAGE>

Dated: _____________________________    Signed: ________________________________
                                                 (Sign exactly as name appears
                                                 on the other side of this
                                                 Security)

Signature Guarantee: ___________________________________________________________

TO BE COMPLETED BY PURCHASER IF (2) ABOVE IS CHECKED

            The undersigned represents and warrants that it is purchasing this
Security for its own account or an account with respect to which it exercises
sole investment discretion and that it and any such account is a "qualified
institutional buyer" within the meaning of Rule 144A under the Securities Act of
1933, as amended, and is aware that the sale to it is being made in reliance on
Rule 144A and acknowledges that it has received such information regarding the
Company as the undersigned has requested pursuant to Rule 144A or has determined
transferor is relying upon the undersigned's foregoing representations in order
to claim the exemption from registration provided by Rule 144A.

Dated: ______________________________   ________________________________________
                                        NOTICE: To be executed by an
                                                executive officer


                                   A-10
<PAGE>

                               CONVERSION NOTICE

To convert this Security into Common Stock of the Company, check the box:

|_|

To convert only part of this Security, state the principal amount to be
converted (must be in multiples of $1,000):

$_______________________________________________________________________________

If you want the stock certificate made out in another person's name, fill in the
form below:

________________________________________________________________________________
(Insert other person's soc. sec. or tax I.D. no.)

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________
(Print or type other person's name, address and zip code)

Date: ___________   Signature(s): ______________________________________________

                                  ______________________________________________
                                  (Signatures must be guaranteed by an "eligible
                                  guarantor institution" meeting the
                                  requirements of the Registrar, which
                                  requirements include membership or
                                  participation in the Security Transfer Agent
                                  Medallion Program ("STAMP") or such other
                                  "signature guarantee program" as may be
                                  determined by the Registrar in addition to, or
                                  in substitution for, STAMP, all in accordance
                                  with the Securities Exchange Act of 1934, as
                                  amended.)


                                      A-11
<PAGE>

Signature(s) guaranteed by: ____________________________________________________
                            (Signatures must be guaranteed by an "eligible
                            guarantor institution" meeting the requirements of
                            the Registrar, which requirements include membership
                            or participation in the Security Transfer Agent
                            Medallion Program ("STAMP") or such other "signature
                            guarantee program" as may be determined by the
                            Registrar in addition to, or in substitution for,
                            STAMP, all in accordance with the Securities
                            Exchange Act of 1934, as amended.)


                                      A-12
<PAGE>

                   OPTION OF HOLDER TO ELECT PURCHASE NOTICE

            If you want to elect to have this Security purchased by the Company
pursuant to Section 3.07 of the Indenture, check the box: |_|

            If you want to elect to have only part of this Security purchased by
the Company pursuant to Section 3.07 of the Indenture, state the principal
amount:

                    $ _____________________________________
                      (in an integral multiple of S 1,000)


Date: ________________                  Signature(s): __________________________


                                        ________________________________________
                                        (Sign exactly as your name(s) appear(s)
                                        on the other side of this Security)

Signature(s) guaranteed by:             ________________________________________
                                        (Signatures must be guaranteed by an
                                        "eligible guarantor institution" meeting
                                        the requirements of the Registrar, which
                                        requirements include membership or
                                        participation in the Security Transfer
                                        Agent Medallion Program ("STAMP") or
                                        such other "signature guarantee program"
                                        as may be determined by the Registrar in
                                        addition to, or in substitution for,
                                        STAMP, all in accordance with the
                                        Securities Exchange Act of 1934, as
                                        amended.)


                                      A-13
<PAGE>

                                                                       EXHIBIT B

                                FORM OF LEGENDS

                          I. PRIVATE PLACEMENT LEGEND

            Each Security issued under the Indenture shall bear a legend (and
any common stock issued upon conversion of such Security shall bear a comparable
legend) substantially in the following form:

            THIS SECURITY (OR ITS PREDECESSOR) WAS ORIGINALLY ISSUED IN A
      TRANSACTION EXEMPT FROM REGISTRATION UNDER THE UNITED STATES SECURITIES
      ACT OF 1933 (THE "SECURITIES ACT"), AND THIS SECURITY AND THE SHARES OF
      COMMON STOCK ISSUABLE UPON CONVERSION HEREOF MAY NOT BE OFFERED, SOLD OR
      OTHERWISE TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR AN APPLICABLE
      EXEMPTION THEREFROM. EACH PURCHASER OF THIS SECURITY IS HEREBY NOTIFIED
      THAT THE SELLER OF THIS SECURITY MAY BE RELYING ON THE EXEMPTION FROM THE
      PROVISIONS OF SECTION 5 OF THE SECURITIES ACT PROVIDED BY RULE 144A
      THEREUNDER.

            THE HOLDER OF THIS SECURITY AGREES FOR THE BENEFIT OF THE ISSUER
      HEREOF THAT (A) THIS SECURITY AND THE SHARES OF COMMON STOCK ISSUABLE UPON
      CONVERSION HEREOF MAY BE OFFERED, RESOLD, PLEDGED OR OTHERWISE
      TRANSFERRED, ONLY (I) IN THE UNITED STATES TO A PERSON WHOM THE SELLER
      REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL BUYER (AS DEFINED IN RULE
      144A UNDER THE SECURITIES ACT) IN A TRANSACTION MEETING THE REQUIREMENTS
      OF RULE 144A, (II) PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE
      SECURITIES ACT PROVIDED BY RULE 144 THEREUNDER (IF AVAILABLE) OR (III)
      PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT,
      IN EACH OF CASES (I) THROUGH (III) IN ACCORDANCE WITH ANY APPLICABLE
      SECURITIES LAWS OF ANY STATE OF THE UNITED STATES, AND (B) THE HOLDER
      WILL, AND EACH SUBSEQUENT HOLDER IS REQUIRED TO, NOTIFY ANY PURCHASER OF
      THIS SECURITY FROM IT OF THE RESALE RESTRICTIONS REFERRED TO IN (A) ABOVE.


                                      B-1
<PAGE>

                           II. GLOBAL SECURITY LEGEND

            Any Global Security authenticated and delivered hereunder shall bear
a legend (which would be in addition to any other legends required in the case
of a Restricted Security) in substantially the following form:

            THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE
      INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF A
      DEPOSITORY OR A NOMINEE OF A DEPOSITORY OR A SUCCESSOR DEPOSITORY. THIS
      SECURITY IS NOT EXCHANGEABLE FOR SECURITIES REGISTERED IN THE NAME OF A
      PERSON OTHER THAN THE DEPOSITORY OR ITS NOMINEE EXCEPT IN THE LIMITED
      CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND NO TRANSFER OF THIS SECURITY
      (OTHER THAN A TRANSFER OF THIS SECURITY AS A WHOLE BY THE DEPOSITORY TO A
      NOMINEE OF THE DEPOSITORY OR BY A NOMINEE OF THE DEPOSITORY TO THE
      DEPOSITORY OR ANOTHER NOMINEE OF THE DEPOSITORY) MAY BE REGISTERED EXCEPT
      IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE.

            UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE
      OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE
      COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE, OR PAYMENT,
      AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN
      SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC
      (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS
      REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR
      OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL
      INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST
      HEREIN.

            TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN
      WHOLE, BUT NOT IN PART, TO NOMINEES OF CEDE & CO. OR TO A SUCCESSOR
      THEREOF OR SUCH SUCCESSOR'S NOMINEE AND TRANSFERS OF PORTIONS OF THIS
      GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE
      RESTRICTIONS SET FORTH IN SECTION 2.16 OF THE INDENTURE.
<PAGE>

                                                                       EXHIBIT C

                           Form of Certificate To Be
                          Delivered in Connection with
                   Transfers to Non-QIB Accredited Investors

                                                                          [Date]

The Chase Manhattan Bank
450 West 33rd Street, 15th Floor
New York, NY 10001
Attention: Capital Markets Fiduciary Services

Ladies and Gentlemen:

            In connection with our proposed purchase of 5 3/4% Convertible
Subordinated Notes Due 2007 (the "Securities") of Alexion Pharmaceuticals, Inc.
(the "Company"), we confirm that:

            1. We have received a copy of the Offering Memorandum (the "Offering
      Memorandum"), dated March 3, 2000, relating to the Securities and such
      other information as we deem necessary in order to make our investment
      decision. We acknowledge that we have read and agreed to the matters
      stated on page 1 of the Offering Memorandum and in the section entitled
      "Notice to Investors" of the Offering Memorandum, including the
      restrictions on duplication and circulation of the Offering Memorandum.

            2. We understand that any subsequent transfer of the Securities is
      subject to certain restrictions and conditions set forth in this Indenture
      relating to the Securities (as described in the Offering Memorandum) and
      the undersigned agrees to be bound by, and not to resell, pledge or
      otherwise transfer the Securities except in compliance with, such
      restrictions and conditions and the Securities Act of 1933, as amended
      (the "Securities Act") and all applicable state securities laws.

            3. We understand that the offer and sale of the Securities have not
      been registered under the Securities Act, and that the Securities may not
      be offered or sold except as permitted in the following sentence. We
      agree, on our own behalf and on behalf of any accounts for which we are
      acting as hereinafter stated, that if we should sell any Securities prior
      to the date that is two years after the original issuance of the
      Securities, we will do so only (i) to the Company or any of its
      subsidiaries, (ii) inside the United States in accordance with Rule 144A
      under the Securities Act to a "qualified institutional buyer" (as defined
      in Rule 144A under the Securities Act), (iii) inside the United States to
      an institutional "accredited investor" (as defined below) that, prior to
      such transfer, furnishes (or has furnished on its behalf by a U.S.
      broker-dealer) to the Trustee (as defined in the Indenture relating to the
      Securities), a signed letter containing certain representations and
      agreements relating to the restrictions on transfer of the Securities (the
      form of which letter can be obtained from the Trustee), (iv) outside the
      United States in accordance with Rule 904 of Regulation S under the
      Securi-


                                      C-1
<PAGE>

      ties Act, (v) pursuant to the exemption from registration provided by Rule
      144 under the Securities Act (if available), or (vi) pursuant to an
      effective registration statement under the Securities Act, and we further
      agree to provide to any person purchasing any of the Securities from us a
      notice advising such purchaser that resales of the Securities are
      restricted as stared herein.

            4. We are not acquiring the Securities for or on behalf of, and will
      not transfer the Securities to, any pension or welfare plan (as defined in
      Section 3 of the Employee Retirement Income Security Act of 1974), except
      as permitted by law.

            5. We understand that, on any proposed resale of any Securities, we
      will be required to furnish to the Trustee and the Company such
      certification, legal opinions and other information as the Trustee and the
      Company may reasonably require to confirm that the proposed sale complies
      with the foregoing restrictions. We further understand that the Securities
      purchased by us will bear a legend to the foregoing effect.

            6. We are an institutional "accredited investor" (as defined in Rule
      50l(a)(1), (2), (3) or (7) of Regulation D under the Securities Act) and
      have such knowledge and experience in financial and business matters as to
      be capable of evaluating the merits and risks of our investment in the
      Securities, and we and any accounts for which we are acting are each able
      to bear the economic risk of our or their investment, as the case may be.

            7. We are acquiring the Securities purchased by us for our account
      or for one or more accounts (each of which is an institutional "accredited
      investor") as to each of which we exercise sole investment discretion.


                                      C-2
<PAGE>

            You, the Company, the Trustee and others are entitled to rely upon
this letter and are irrevocably authorized to produce this letter or a copy
hereof to any interested party in any administrative or legal proceeding or
official inquiry with respect to the matters covered hereby.

                                        Very truly yours,

                                        [Name of Transferee]


                                        By: ____________________________________
                                            Name:
                                            Title:


                                      C-3
<PAGE>

                                                                       EXHIBIT D

                      Form of Certificate To Be Delivered
                          in Connection with Transfers
                            Pursuant to Regulation S

                                                                          [Date]

The Chase Manhattan Bank
450 West 33rd Street, 15th Floor
New York, NY 10001
Attention: Capital Markets Fiduciary Services

                  Re: Alexion Pharmaceuticals, Inc. (the "Company")
                      5 3/4% Convertible Subordinated Notes
                      due 2007 (the "Securities")

Ladies and Gentlemen:

            In connection with our proposed purchase of $       aggregate
principal amount of the Securities, we confirm that such purchase has been
effected pursuant to and in accordance with Regulation S under the U.S.
Securities Act of 1933, as amended (the "Securities Act"), and, accordingly, we
represent that:

            (1)* [We are not a U.S. person and are not acquiring the Securities
      for the account or benefit of any U.S. person]. [We are a U.S. person who
      purchased securities in a transaction that did not require registration
      under the Act.]

            (2) We agree to resell the Securities only in accordance with the
      provisions of Regulation S, pursuant to registration under the Securities
      Act, or pursuant to an available exemption from registration; and we agree
      not to engage in hedging transactions with regard to such securities
      unless in compliance with the Securities Act.

----------
*     One of the two following sentences must be used.


                                      D-1
<PAGE>

            You, the Company and counsel for the Company are entitled to rely
upon this letter and are irrevocably authorized to produce this letter or a copy
hereof to any interested party in any administrative or legal proceedings or
official inquiry with respect to the matters covered hereby. Terms used in this
certificate have the meanings set forth in Regulation S.

                                        Very truly yours,

                                        [Name of Transferor]


                                        By: ____________________________________
                                            Authorized Signature


                                      D-2
<PAGE>

                                                                       EXHIBIT E

         Form of Notice of Transfer Pursuant to Registration Statement

                                                                          [Date]

Alexion Pharmaceuticals, Inc.
25 Science Park
New Haven, Connecticut 06511

The Chase Manhattan Bank
450 West 33rd Street, 15th Floor
New York, NY
Attention: Capital Markets Fiduciary Services

            Re: Alexion Pharmaceuticals, Inc. (the "Company")
                5 3/4% Convertible Subordinated Notes Due 2007
                (the "Securities")

Ladies and Gentlemen:

            Please be advised that ______________ has transferred $ ____________
aggregate principal amount of the Securities or __ shares of the Company's
common stock, $0.0001 par value per share, issuable on conversion of the
Securities ("Stock") pursuant to an effective Shelf Registration Statement on
Form S-3 (File No. 333-     ) filed by the Company.

            We hereby certify that the prospectus delivery requirements, if any,
of the Securities Act of 1933 as amended, have been satisfied with respect to
the transfer described above and that the above-named beneficial owner of the
Securities or Stock is named as a "Selling Security Holder" in the Prospectus
dated        or in amendments or supplements thereto, and that the aggregate
principal amount of the Securities, or number of shares of Stock transferred are
[a portion of] the Securities or Stock listed in such Prospectus, as amended or
supplemented, opposite such owner's name.

                                        Very truly yours,


                                        ________________________________________
                                                      (Name)


                                      E-1
<PAGE>

                                                                       EXHIBIT F

    Form of Opinion of Counsel in Connection with Registration of Securities

                                                                          [Date]

The Chase Manhattan Bank
450 West 33rd Street, 15th Floor
New York, NY 10001
Attention: Capital Markets Fiduciary Services

            Re: Alexion Pharmaceuticals, Inc. (the "Company")
                5 3/4% Subordinated Convertible Notes Due 2007
                (the "Securities")

Ladies and Gentlemen:

            Reference is made to the Securities issued pursuant to a certain
indenture dated as of March 1, 2000 by and between the Company and The Chase
Manhattan Bank, as trustee (the "Trustee"). The Securities were issued in
transactions exempt from registration under the Securities Act of 1933, as
amended (the "Securities Act"). The Company has filed with the Securities and
Exchange Commission (the "SEC") a registration statement on Form S-3 (number
333-______) (the "Registration Statement") relating to the registration under
the Securities Act of $[______________] principal amount of the Securities and
the shares of Common Stock of the Company (the "Shares") issuable upon
conversion of the Securities being registered. The Registration Statement was
declared effective by order of the SEC dated [_____].

            We have acted as counsel for the Company in connection with the
issuance of the Securities and the preparation and filing of the Registration
Statement and are familiar with the Securities, the Indenture, the Registration
Statement, the above-mentioned SEC order and such other documents as are
necessary to render this opinion.

            Based on the foregoing, it is our opinion that (1) the Registration
Statement has become and is currently effective under the Securities act so that
the Securities covered thereby and the Shares issuable upon conversion of such
Securities are duly registered under the Securities Act; and (2) the Indenture
has been duly qualified under the Trust Indenture Act of 1939, as amended.

                                        Yours truly,


                                      F-1