<PAGE>

                                                                     Exhibit 4.1

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                                ICOS CORPORATION

                                       and

                    WELLS FARGO BANK, NATIONAL ASSOCIATIONS,

                                   as Trustee

                                   ----------

                                    INDENTURE

                            Dated as of June 20, 2003

                                   ----------

               2% Convertible Subordinated Notes Due July 1, 2023

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

<PAGE>

                              CROSS-REFERENCE TABLE

Trust Indenture                                                        Indenture
  Act Section                                                           Section
---------------                                                       ----------

310 (a)(1)..........................................................  8.10
    (a)(2)..........................................................  8.10
    (a)(3)..........................................................  N.A.
    (a)(4)..........................................................  N.A.
    (a)(5)..........................................................  N.A.
    (b).............................................................  8.08; 8.10
    (c).............................................................  N.A.

311 (a).............................................................  8.11
    (b).............................................................  8.11
    (c).............................................................  N.A.

312 (a).............................................................  2.05
    (b).............................................................  13.03
    (c).............................................................  13.03

313 (a).............................................................  8.06
    (b)(1)..........................................................  N.A.
    (b)(2)..........................................................  8.06
    (c).............................................................  8.06
    (d).............................................................  8.06

314 (a).............................................................  5.02; 5.03
    (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).............................................................  8.01(b)
    (b).............................................................  8.05
    (c).............................................................  8.01(a)
    (d).............................................................  8.01(c)
    (e).............................................................  7.11

316 (a) (last sentence).............................................  2.09
    (a) (1)(A)......................................................  7.05
    (a) (1)(B)......................................................  7.04
    (a) (2) ........................................................  N.A.
    (b).............................................................  7.07
    (c).............................................................  N.A.

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Trust Indenture                                                        Indenture
  Act Section                                                           Section
---------------                                                       ----------

317 (a)(1)..........................................................  7.08
    (a)(2)..........................................................  7.09
    (b).............................................................  2.04

318 (a).............................................................  13.01

----------
N.A. means Not Applicable.

NOTE: This  Cross-Reference  Table shall not, for any purpose, be deemed to be a
         part of the Indenture.

<PAGE>

                                    CONTENTS

ARTICLE 1.  DEFINITIONS AND INCORPORATION BY REFERENCE........................1

     SECTION 1.01.  DEFINITIONS...............................................1

     SECTION 1.02.  OTHER DEFINITIONS.........................................4

     SECTION 1.03.  INCORPORATION BY REFERENCE OF TRUST INDENTURE ACT.........5

     SECTION 1.04.  RULES OF CONSTRUCTION.....................................5

ARTICLE 2.  THE SECURITIES....................................................6

     SECTION 2.01.  FORM AND DATING...........................................6

     SECTION 2.02.  EXECUTION AND AUTHENTICATION..............................7

     SECTION 2.03.  REGISTRAR, PAYING AGENT, CONVERSION AGENT AND
            NEW YORK PRESENTING AGENT.........................................8

     SECTION 2.04.  PAYMENT ON SECURITIES; 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...................................10

     SECTION 2.08.  OUTSTANDING SECURITIES...................................11

     SECTION 2.09.  TREASURY SECURITIES......................................11

     SECTION 2.10.  TEMPORARY SECURITIES.....................................11

     SECTION 2.11.  CANCELLATION.............................................11

     SECTION 2.12.  DEFAULTED INTEREST.......................................12

     SECTION 2.13.  CUSIP NUMBERS............................................12

     SECTION 2.14.  ADDITIONAL TRANSFER AND EXCHANGE REQUIREMENTS............12

                                      -i-

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ARTICLE 3.  REDEMPTION.......................................................18

     SECTION 3.01.  OPTIONAL REDEMPTION; NOTICE TO TRUSTEE...................18

     SECTION 3.02.  SELECTION OF SECURITIES TO BE REDEEMED...................19

     SECTION 3.03.  NOTICE OF REDEMPTION.....................................19

     SECTION 3.04.  EFFECT OF NOTICE OF REDEMPTION...........................20

     SECTION 3.05.  DEPOSIT OF REDEMPTION PRICE..............................20

     SECTION 3.06.  SECURITIES REDEEMED IN PART..............................20

ARTICLE 4.  REPURCHASES......................................................21

     SECTION 4.01.  PURCHASE OF SECURITIES AT OPTION OF THE HOLDER...........21

     SECTION 4.02.  REPURCHASE UPON FUNDAMENTAL CHANGE.......................25

     SECTION 4.03.  NOTICES, ETC.............................................25

     SECTION 4.04.  EXERCISING FUNDAMENTAL CHANGE REPURCHASE RIGHT...........25

     SECTION 4.05.  CERTAIN DEFINITIONS......................................26

ARTICLE 5.  COVENANTS........................................................28

     SECTION 5.01.  PAYMENT OF SECURITIES....................................28

     SECTION 5.02.  COMMISSION REPORTS.......................................28

     SECTION 5.03.  COMPLIANCE CERTIFICATE...................................28

     SECTION 5.04.  CORPORATE EXISTENCE......................................29

     SECTION 5.05.  NOTICE OF DEFAULTS.......................................29

     SECTION 5.06.  FURTHER INSTRUMENTS AND ACTS.............................29

     SECTION 5.07.  RESALE OF CERTAIN SECURITIES.............................29

                                      -ii-

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     SECTION 5.08.  REGISTRATION RIGHTS......................................29

ARTICLE 6.  SUCCESSORS.......................................................31

     SECTION 6.01.  WHEN COMPANY MAY MERGE, ETC..............................31

ARTICLE 7.  DEFAULTS AND REMEDIES............................................32

     SECTION 7.01.  EVENTS OF DEFAULT........................................32

     SECTION 7.02.  ACCELERATION.............................................33

     SECTION 7.03.  OTHER REMEDIES...........................................34

     SECTION 7.04.  WAIVER OF PAST DEFAULTS..................................34

     SECTION 7.05.  CONTROL BY MAJORITY......................................34

     SECTION 7.06.  LIMITATION ON SUITS......................................34

     SECTION 7.07.  RIGHTS OF HOLDERS TO RECEIVE PAYMENT.....................35

     SECTION 7.08.  COLLECTION SUIT BY TRUSTEE...............................35

     SECTION 7.09.  TRUSTEE MAY FILE PROOFS OF CLAIM.........................35

     SECTION 7.10.  PRIORITIES...............................................36

     SECTION 7.11.  UNDERTAKING FOR COSTS....................................36

ARTICLE 8.  TRUSTEE..........................................................37

     SECTION 8.01.  DUTIES OF TRUSTEE........................................37

     SECTION 8.02.  RIGHTS OF TRUSTEE........................................38

     SECTION 8.03.  INDIVIDUAL RIGHTS OF TRUSTEE.............................38

     SECTION 8.04.  TRUSTEE'S DISCLAIMER.....................................39

     SECTION 8.05.  NOTICE OF DEFAULTS.......................................39

     SECTION 8.06.  REPORTS BY TRUSTEE TO HOLDERS............................39

     SECTION 8.07.  COMPENSATION AND INDEMNITY...............................39

     SECTION 8.08.  REPLACEMENT OF TRUSTEE...................................40

                                     -iii-

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     SECTION 8.09.  SUCCESSOR TRUSTEE, AGENTS BY MERGER, ETC.................41

     SECTION 8.10.  ELIGIBILITY; DISQUALIFICATION............................41

     SECTION 8.11.  PREFERENTIAL COLLECTION OF CLAIMS AGAINST COMPANY........42

ARTICLE 9.  DISCHARGE OF INDENTURE...........................................42

     SECTION 9.01.  TERMINATION OF COMPANY'S OBLIGATIONS.....................42

     SECTION 9.02.  APPLICATION OF TRUST MONEY...............................43

     SECTION 9.03.  REPAYMENT TO COMPANY.....................................43

     SECTION 9.04.  INDEMNITY FOR GOVERNMENT OBLIGATIONS.....................43

     SECTION 9.05.  REINSTATEMENT............................................43

ARTICLE 10. AMENDMENTS, SUPPLEMENTS AND WAIVERS..............................44

     SECTION 10.01. WITHOUT CONSENT OF HOLDERS...............................44

     SECTION 10.02. WITH CONSENT OF HOLDERS..................................44

     SECTION 10.03. COMPLIANCE WITH TRUST INDENTURE ACT......................45

     SECTION 10.04. REVOCATION AND EFFECT OF CONSENTS........................45

     SECTION 10.05. NOTATION ON OR EXCHANGE OF SECURITIES....................46

     SECTION 10.06. TRUSTEE TO SIGN AMENDMENTS, ETC..........................46

ARTICLE 11. CONVERSION.......................................................46

     SECTION 11.01. CONVERSION PRIVILEGE.....................................46

     SECTION 11.02. CONVERSION PROCEDURE.....................................47

     SECTION 11.03. FRACTIONAL SHARES........................................47

     SECTION 11.04. TAXES ON CONVERSION......................................48

     SECTION 11.05. COMPANY TO PROVIDE STOCK.................................48

                                      -iv-

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     SECTION 11.06. ADJUSTMENT FOR CHANGE IN CAPITAL STOCK...................48

     SECTION 11.07. ADJUSTMENT FOR RIGHTS ISSUE..............................49

     SECTION 11.08. ADJUSTMENT FOR CERTAIN DISTRIBUTIONS.....................50

     SECTION 11.09. ADJUSTMENT FOR ALL CASH DISTRIBUTION.....................51

     SECTION 11.10. ADJUSTMENT FOR TENDER OR EXCHANGE OFFER..................52

     SECTION 11.11. CURRENT MARKET PRICE.....................................53

     SECTION 11.12. WHEN ADJUSTMENT MAY BE DEFERRED..........................53

     SECTION 11.13. WHEN NO ADJUSTMENT REQUIRED..............................53

     SECTION 11.14. NOTICE OF ADJUSTMENT.....................................54

     SECTION 11.15. VOLUNTARY REDUCTION......................................54

     SECTION 11.16. NOTICE OF CERTAIN TRANSACTIONS...........................55

     SECTION 11.17. PROVISIONS IN CASE OF CONSOLIDATION, MERGER
            OF THE COMPANY OR TRANSFER OR LEASE..............................55

     SECTION 11.18. COMPANY DETERMINATION FINAL..............................56

     SECTION 11.19. TRUSTEE'S DISCLAIMER...................../...............56

ARTICLE 12. SUBORDINATION....................................................56

     SECTION 12.01. AGREEMENT TO SUBORDINATE.................................56

     SECTION 12.02. CERTAIN DEFINITIONS......................................56

     SECTION 12.03. LIQUIDATION; DISSOLUTION; BANKRUPTCY.....................57

     SECTION 12.04. COMPANY NOT TO MAKE PAYMENTS WITH RESPECT
            TO SECURITIES IN CERTAIN CIRCUMSTANCES...........................58

     SECTION 12.05. ACCELERATION OF SECURITIES...............................58

     SECTION 12.06. WHEN DISTRIBUTION MUST BE PAID OVER......................58

                                       -v-

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     SECTION 12.07. NOTICE BY COMPANY........................................59

     SECTION 12.08. SUBROGATION..............................................59

     SECTION 12.09. RELATIVE RIGHTS..........................................59

     SECTION 12.10. SUBORDINATION MAY NOT BE IMPAIRED BY COMPANY.............59

     SECTION 12.11. DISTRIBUTION OR NOTICE TO REPRESENTATIVE.................59

     SECTION 12.12. RIGHTS OF TRUSTEE AND PAYING AGENT.......................60

     SECTION 12.13. EFFECTUATION OF SUBORDINATION BY TRUSTEE.................61

ARTICLE 13. MISCELLANEOUS....................................................61

     SECTION 13.01. TRUST INDENTURE ACT CONTROLS.............................61

     SECTION 13.02. NOTICES..................................................61

     SECTION 13.03. COMMUNICATIONS BY HOLDERS WITH OTHER HOLDERS.............62

     SECTION 13.04. CERTIFICATE AND OPINION AS TO CONDITIONS PRECEDENT.......62

     SECTION 13.05. STATEMENTS REQUIRED IN CERTIFICATE OR OPINION............63

     SECTION 13.06. RULES BY TRUSTEE AND AGENTS..............................63

     SECTION 13.07. LEGAL HOLIDAYS...........................................63

     SECTION 13.08. GOVERNING LAW............................................63

     SECTION 13.09. NO RECOURSE AGAINST OTHERS...............................63

     SECTION 13.10. SUCCESSORS...............................................64

     SECTION 13.11. COUNTERPART ORIGINALS....................................64

     SECTION 13.12. SEVERABILITY.............................................64

EXHIBIT A FORM OF SECURITY..................................................A-1

                                      -vi-

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NOTE: This Table of Contents shall not, for any purpose,  be deemed to be a part
      of the Indenture.

                                     -vii-

<PAGE>

     INDENTURE dated as of June 20, 2003, between ICOS CORPORATION, a Delaware
corporation (the "Company"), and Wells Fargo Bank, National Association, a
national banking association organized under the laws of the United States (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 2% Convertible
Subordinated Notes Due July 1, 2023 (the "Security" or "Securities"):

                                   ARTICLE 1.

                   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
the purposes of this definition, "control" when used with respect to any
specified Person means the power to direct the management and policies of such
Person, directly or indirectly, whether through the ownership of voting
securities, by contract or otherwise, and the terms "controlling" and
"controlled" have meanings correlative to the foregoing.

     "Agent" means any Registrar, Paying Agent, Conversion Agent, New York
Presenting Agent or Co-Registrar.

     "Applicable Procedures" means, with respect to any transfer or transaction
involving a Global Security or, beneficial interest therein, the rules and
procedures of the Depositary that are applicable to such transfer or transaction
and as in effect from time to time.

     "Board of Directors" or "Board" means the Board of Directors of the Company
or any duly authorized committee of the Board.

     "Business Day" means any day that is not a Legal Holiday.

     "Certificated Security" means a Security that is in substantially the form
attached hereto as EXHIBIT A and that does not include the information or the
schedule called for by footnotes 1, 3 and 4 thereof.

     "Common Stock" shall mean the Company's common stock, $0.01 par value per
share, as it exists on the date of this Indenture or any other capital stock of
the Company into which such Common Stock shall be reclassified or changed.

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

<PAGE>

     "Corporate Trust Office" means the principal office of the Trustee at 707
Wilshire Blvd., 17/th/ Floor, Los Angeles, CA 90017, Attention: Corporate Trust
Department  (ICOS  Corporation,  2% Convertible  Subordinated  Notes due July 1,
2023), or such other office,  designated by the Trustee by written notice to the
Company  and  approved  by the  Company,  at  which at any  particular  time its
corporate trust business shall be administered.

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

     "Global Security" means a permanent Global Security that is in
substantially the form attached hereto as EXHIBIT A and that includes the
information and schedule called for by footnotes 1, 3 and 4 thereof and which is
deposited with the Depositary or its custodian and registered in the name of the
Depositary or its nominee.

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

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

     "Initial Purchasers Option" means the option granted by the Company to the
Initial Purchasers to purchase up to $50,000,000 aggregate principal amount of
additional Securities pursuant to the Purchase Agreement.

     "Officer" means the Chairman, the President, Vice President, Secretary,
General Counsel or the Treasurer of the Company.

     "Officers' Certificate" means a certificate signed by two Officers. See
Sections 13.04 and 13.05.

     "Opinion of Counsel" means a written opinion from legal counsel who is
acceptable to the Trustee. The counsel may be an employee of or counsel to the
Company. See Sections 13.04 and 13.05.

     "Person" means any individual, corporation, limited liability company,
partnership, joint venture, association, joint-stock company, trust,
unincorporated organization or government or any agency or political subdivision
thereof and, for purposes of Article 4, shall have the additional meaning set
forth in Section 4.04(c).

     "Purchase Agreement" means the Purchase Agreement, dated June 16, 2003,
among the Company and Credit Suisse First Boston LLC and Goldman, Sachs & Co. as
representatives for the initial purchasers (collectively, the "Initial
Purchasers").

     "Quoted Prices" means the price per share of Common Stock on the relevant
date, determined on the basis of the last reported sale price regular way of the
Common Stock or, in case no such sale takes place on such day, the average of
the closing bid and asked prices

                                       -2-

<PAGE>

regular way of the Common Stock, in either case, at 4:00 p.m. (or such earlier
time as the last sale prior to 4:00 p.m.), New York City time, on the New York
Stock Exchange Composite Tape, or, if the Common Stock is not listed or admitted
to trading on such Exchange, as reported on the national securities exchange in
or nearest the City of New York on which the Common Stock is listed or admitted
to trading, or if the Common Stock is not listed or admitted to trading on any
national securities exchange, the last reported sale price regular way of the
Common Stock or, in case no such sale takes place on such day, the average of
the highest reported bid and lowest reported asked prices of the Common Stock as
furnished by the National Association of Securities Dealers, Inc. through Nasdaq
or a similar organization if Nasdaq is no longer reporting such information, or
if on any such day the Common Stock is not quoted by any such organization, the
average of the highest reported bid and lowest reported asked prices of the
Common Stock as available in any other over-the-counter market, or if on such
day the Common Stock is not reported in any such market, the fair value of a
share of Common Stock on such day, as determined in good faith by, and evidenced
by a resolution of, the Board of Directors.

     "Record Date," has the meaning set forth in the applicable Section.

     "Restricted Certificated Security" means a Certificated Security which is a
Transfer Restricted Security.

     "Restricted Global Security" means a Global Security that is a Transfer
Restricted Security.

     "Rule 144" means Rule 144 under the Securities Act or any successor to such
Rule.

     "SEC" means the Securities and Exchange Commission.

     "Security" or "Securities" means the Securities described above issued,
authenticated and delivered under this Indenture.

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

     "Securities Custodian" means Wells Fargo Bank, National Association, as
custodian with respect to the Securities in global form, or any successor entity
thereto.

     "Subsidiary" means a corporation, a majority of the voting stock of which
is owned, directly or indirectly, by the Company or by one or more Subsidiaries,
or by the Company and one or more other Subsidiaries.

     "TIA" means the Trust Indenture Act of 1939, as amended by the Trust
Indenture Reform Act of 1990 and as in effect on the date of this Indenture,
except to the extent any amendment to the Trust Indenture Act expressly provides
for application of the Trust Indenture Act as in effect on another date.

                                       -3-

<PAGE>

     "Trading Day" means each Monday, Tuesday, Wednesday, Thursday and Friday
other than any day on which securities are not traded on the principal exchange
or market on which the securities in question are traded.

     "Trust Officer" means any officer or assistant officer of the Trustee
assigned by the Trustee to administer its corporate trust matters.

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

     "Unrestricted Global Security" means a Global Security that is not a
Transfer Restricted Security.

SECTION 1.02.  OTHER DEFINITIONS

Term                                                          Defined in Section
----                                                          ------------------
"Agent Members".............................................................2.01
"Bankruptcy Law"............................................................7.01
"Capital Stock"..........................................................4.05(a)
"Company Notice".........................................................4.01(c)
"Conversion Agent"..........................................................2.03
"Current Market Price".....................................................11.11
"Custodian".................................................................7.01
"Depositary".............................................................2.01(a)
"DTC"....................................................................2.01(a)
"Event of Default"..........................................................7.01
"Exchange Act"...........................................................4.05(b)
"Expiration Time"..........................................................11.10
"Final Surrender Date"......................................................4.04
"Fundamental Change".....................................................4.05(b)
"Fundamental Change Company Notice".........................................4.03
"Fundamental Change Purchase Date".......................................4.04(a)
"Fundamental Change Purchase Price".........................................4.02
"Legal Holiday"............................................................13.07
"New York Presenting Agent".................................................2.03
"Paying Agent"..............................................................2.03
"Purchase Date"..........................................................4.01(a)
"Purchase Notice"...........................................................4.01
"Purchase Price"............................................................4.01
"Purchased Shares".........................................................11.10
"QIB"....................................................................2.01(a)
"Registrar".................................................................2.03
"Registration Default"......................................................5.08

                                       -4-

<PAGE>

Term                                                          Defined in Section
----                                                          ------------------
"Registration Rights Agreement".............................................2.06
"Representative"...........................................................12.02
"Senior Indebtedness"......................................................12.02
"Shelf Registration Statement"..............................................5.08
"Transfer Certificate"...................................................2.14(f)
"Transfer Restricted Securities".........................................2.14(f)
"U.S. Government Obligations"...............................................9.01
"Voting Shares"..........................................................4.05(d)

Whenever the definition contained in such section limits its application to the
term as used in specific sections, the foregoing shall not be deemed to expand
the application of such definition to the term as used in any section other than
such specific sections.

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 Securityholder.

     "INDENTURE TO BE QUALIFIED" means this Indenture.

     "INDENTURE TRUSTEE" or "INSTITUTIONAL TRUSTEE" means the Trustee.

     "OBLIGOR" on the indenture securities means the Company or any other
obligor on the Securities.

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

SECTION 1.04.  RULES OF CONSTRUCTION

     Unless the context otherwise requires:

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

     (b)  an accounting term not otherwise defined has the meaning assigned to
          it in accordance with generally accepted accounting principles;

                                       -5-

<PAGE>

     (c)  "or" is not exclusive;

     (d)  words in the singular include the plural, and words in the plural
          include the singular; and

     (e)  provisions apply to successive events and transactions.

                                   ARTICLE 2.

                                 THE SECURITIES

SECTION 2.01.  FORM AND DATING

     The Securities shall be substantially in the form set forth in EXHIBIT A,
which Exhibit is incorporated in and made 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. The
Securities are being offered and sold by the Company pursuant to the Purchase
Agreement in transactions exempt from, or not subject to, the registration
requirements of the Securities Act.

     (a)  RESTRICTED GLOBAL SECURITIES. Securities offered and sold to qualified
institutional buyers as defined in Rule 144A (collectively, "QIBs" or
individually, each a "QIB") in reliance on Rule 144A under the Securities Act or
outside the United States in an offshore transaction in accordance with
Regulation S under the Securities Act shall be issued initially in the form of
one or more Restricted Global Securities, which shall be deposited on behalf of
the purchasers of the Securities represented thereby with the Trustee, at its
Corporate Trust Office, as custodian for the depositary, The Depository Trust
Company ("DTC") (such depositary, or any successor thereto, being hereinafter
referred to as the "Depositary"), and registered in the name of its nominee,
Cede & Co., duly executed by the Company and authenticated by the Trustee as
hereinafter provided. The aggregate principal amount of the Restricted Global
Security may from time to time be increased or decreased by adjustments made on
the records of the Securities Custodian as hereinafter provided, subject in each
case to compliance with the Applicable Procedures.

     (b)  GLOBAL SECURITIES IN GENERAL. Each Global Security shall represent
such of the outstanding Securities as shall be specified therein and each shall
provide that it shall represent the aggregate amount of outstanding Securities
from time to time endorsed thereon and that the aggregate amount of outstanding
Securities represented thereby may from time to time be reduced or increased, as
appropriate, to reflect exchanges, redemptions, purchases or conversions of such
Securities. Any endorsement of a Global Security to reflect the amount of any
increase or decrease in the amount of outstanding Securities represented thereby
shall be made by the Securities Custodian in accordance with the standing
instructions and procedures existing between the Depositary and the Securities
Custodian.

                                       -6-

<PAGE>

     Members of, or participants in, the Depositary ("Agent Members") shall have
no rights under this Indenture with respect to any Global Security held on their
behalf by the Depositary or under any Global Security, and the Depositary
(including, for this purpose, its nominee) may be treated by the Company, the
Trustee and any agent of the Company or the Trustee as the absolute owner and
Holder of such Global Security for all purposes whatsoever. Notwithstanding the
foregoing, nothing herein shall (A) 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 Depositary or (B)
impair, as between the Depositary and its Agent Members, the operation of
customary practices governing the exercise of the rights of a Holder of any
Security.

     (c)  CERTIFICATED SECURITIES. Certificated Securities shall be issued only
under the limited circumstances provided in Section 2.14(a)(1) hereof.

SECTION 2.02.  EXECUTION AND AUTHENTICATION

     Two Officers shall sign the Securities on behalf of the Company by manual
or facsimile signature. The Company's seal shall be reproduced on the
Securities.

     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 Trustee's signature shall be conclusive evidence that the
Security has been authenticated under this Indenture.

     The Trustee shall authenticate and make available for delivery Securities
for original issue in an aggregate principal amount of $250,000,000 upon a
Company order without any further action by the Company; PROVIDED, HOWEVER, that
in the event that the Company sells any Securities pursuant to the Initial
Purchaser Option, then the Trustee shall authenticate and deliver Securities for
original issue in an aggregate principal amount of $250,000,000 plus up to an
additional $50,000,000 aggregate principal amount of the Securities sold
pursuant to the Initial Purchaser Option upon a Company order without any
further action by the Company. The aggregate principal amount of the Securities
outstanding at any time may not exceed the amount set forth in the foregoing
sentence, subject to the proviso set forth therein, except as provided in
Section 2.07.

     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, other than upon original issuance or pursuant to
Section 2.07. 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.

                                       -7-

<PAGE>

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

SECTION 2.03.  REGISTRAR, PAYING AGENT, CONVERSION AGENT AND NEW YORK PRESENTING
     AGENT

     The Company shall maintain an office or agency where Securities may be
presented for registration of transfer or exchange (the "Registrar"), an office
or agency where Securities may be presented for payment (the "Paying Agent") and
an office or agency where Securities may be presented for conversion (the
"Conversion Agent"). The Registrar shall keep a register of the Securities and
of their transfer and exchange. The Company may appoint one or more
Co-Registrars, one or more additional Paying Agents and one or more additional
Conversion Agents. The Company may act as Registrar, Paying Agent, Conversion
Agent or Co-Registrar. The term "Paying Agent" includes any additional paying
agent; the term "Conversion Agent" includes any additional conversion agent. The
Company shall notify the Trustee of the name and address of any Agent not a
party to this Indenture and shall give the Trustee at least thirty days' notice
prior to changing the Registrar, Paying Agent or Conversion Agent. 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.

     If there is not at least one of each such Registrar or Co-Registrar, Paying
Agent and Conversion Agent located in the Borough of Manhattan, the City of New
York, the Company shall also maintain an office in the Borough of Manhattan, the
City of New York where the securities may be presented for purposes of transfer
and exchange, payment and conversion (the "New York Presenting Agent"). The
Company initially appoints Wells Fargo Bank, National Association having an
office at 45 Broadway, 12/th/ Floor, New York, NY 10006, to serve as New York
Presenting Agent.

SECTION 2.04.  PAYMENT ON SECURITIES; PAYING AGENT TO HOLD MONEY IN TRUST

     (a)  Subject to the following provisions, no later than 11:00 a.m. on the
due date of principal of and premium, if any, and interest on the Securities,
the Company will pay to the Paying Agent in immediately available funds the
amounts, in money of the United States that at the time of payment is legal
tender for payment of public or private debts, in the manner, at the times and
for the purposes set forth herein and in the text of the Securities, and the
Company hereby authorizes and directs the Paying Agent from funds so paid to it
to make or cause to be made payment of the principal of and premium, if any, and
interest on the Securities set forth herein and in the text of the Securities.
The Paying Agent will make payment, from the funds furnished by the Company, of
the principal of and premium, if any, and interest on the Securities by check
drawn upon a bank in the city in which the Paying Agent's principal office is
located, or make payment by wire transfer upon terms acceptable to the Paying
Agent.

                                       -8-

<PAGE>

     (b)  Interest on a Security (other than defaulted interest) shall be paid
on each interest payment date to the Holder thereof at the close of business on
the relevant record date specified in the Securities. Principal of and premium,
if any, on Securities shall be payable only against presentation and surrender
thereof at the principal office of the Paying Agent, unless the Company shall
have otherwise instructed the Trustee in writing.

     (c)  The Company shall require each Paying Agent other than the Trustee to
agree in writing that the Paying Agent will hold in trust for the benefit of
Securityholders or the Trustee all money held by the Paying Agent for the
payment of principal of or premium, if any, or interest on the Securities, and
will 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. If the Company acts as Paying
Agent, it shall segregate the money held by it for the payment of principal of
and premium, if any, and interest on the Securities and hold it as a separate
trust fund. The Company shall provide ten days prior written notice to the
Trustee that it is to act as Paying Agent with respect to such payment and the
Trustee may rely on such notice. The Company at any time may require a Paying
Agent to pay all money held by the Paying Agent to the Trustee. Upon doing so
the Paying Agent shall have no further liability for the money so paid.

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
Securityholders. If the Trustee is not the Registrar, the Company shall furnish
to the Trustee not less than five days prior to 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 Securityholders.

SECTION 2.06.  TRANSFER AND EXCHANGE

     (a)  Subject to compliance with any applicable additional requirements
contained in Section 2.14, when a Security is presented to a Registrar with a
request to register a transfer thereof or to exchange such Security for an equal
principal amount of Securities of other authorized denominations, the Registrar
shall register the transfer or make the exchange as requested; PROVIDED,
HOWEVER, that every Security presented or surrendered for registration of
transfer or exchange shall be duly endorsed or accompanied by an assignment form
and, if applicable, a transfer certificate each in the form included in EXHIBIT
A, and in form satisfactory to the Registrar duly executed by the Holder thereof
or its attorney duly authorized in writing. To permit registration of transfers
and exchanges, upon surrender of any Security for registration of transfer or
exchange at an office or agency maintained pursuant to Section 2.03, the Company
shall execute and the Trustee shall authenticate Securities of a like aggregate
principal amount at the Registrar's request. Any exchange or transfer shall be
without charge, except that the Company or the Registrar may require payment of
a sum sufficient to cover any tax or other governmental charge that may be

                                       -9-

<PAGE>

imposed in relation thereto, and provided, that this sentence shall not apply to
any exchange pursuant to Section 2.07, 2.10, 2.14(a)(1), 3.06, 4.01(g), 4.04(d),
10.05 or 11.02.

     Neither the Company, any Registrar nor the Trustee shall be required to
exchange or register a transfer of (a) any Securities for a period of 15 days
next preceding any mailing of a notice of Securities to be redeemed, (b) any
Securities or portions thereof selected or called for redemption (except, in the
case of redemption of a Security in part, the portion not to be redeemed) or (c)
any Securities or portions thereof in respect of which a Purchase Notice has
been delivered and not withdrawn by the Holder thereof (except, in the case of
the purchase of a Security in part, the portion not to be purchased).

     All Securities issued upon any transfer or exchange of Securities shall be
valid obligations of the Company, evidencing the same debt and entitled to the
same benefits under this Indenture, as the Securities surrendered upon such
transfer or exchange.

     (b)  Any Registrar appointed pursuant to Section 2.03 hereof shall provide
to the Trustee such information as the Trustee may reasonably require in
connection with the delivery by such Registrar of Securities upon transfer or
exchange of Securities.

     (c)  Each Holder of a Security agrees to indemnify the Company and the
Trustee against any liability that may result from the transfer, exchange or
assignment of such Holder's Security in violation of any provision of this
Indenture and/or applicable United States federal or state securities law.

     The Trustee shall have no obligation or duty to monitor, determine or
inquire as to compliance with any restrictions on transfer imposed under this
Indenture or under applicable law with respect to any transfer of any interest
in any Security (including any transfers between or among Agent Members or other
beneficial owners of interests in any Global Security) other than to require
delivery of such certificates and other documentation or evidence as are
expressly required by, and to do so if and when expressly required by the terms
of, this Indenture, and the Registration Rights Agreement relating to the
Securities (the "Registration Rights Agreement") and to examine the same to
determine substantial compliance as to form with the express requirements
hereof.

SECTION 2.07.  REPLACEMENT SECURITIES

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

                                      -10-

<PAGE>

     Every replacement Security shall be an additional obligation of the
Company.

SECTION 2.08.  OUTSTANDING SECURITIES

     The Securities outstanding at any time are all Securities authenticated by
the Trustee (or an authenticating agent appointed pursuant to Section 2.02)
except for those cancelled by the Trustee, those delivered to the Trustee for
cancellation, those reductions in the interests in a global Security effected by
the Trustee hereunder, and those described in this Section as not outstanding.

     A Security does not cease to be outstanding because the Company or an
Affiliate 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 that the
replaced Security is held by a bona fide purchaser.

     If Securities are considered paid under Section 5.01, they cease to be
outstanding and interest on them ceases to accrue.

SECTION 2.09.  TREASURY SECURITIES

     In determining whether the Holders of the required principal amount of
Securities have concurred in any direction, waiver or consent, Securities owned
by the Company 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 the Trustee 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 execute 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.
Every temporary Security shall be executed by the Company and authenticated by
the Trustee, and registered by the Registrar, upon the conditions, and with like
effect, as a definitive Security. 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 promptly
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,

                                      -11-

<PAGE>

payment, conversion or cancellation and may destroy cancelled Securities and
deliver a certificate of such destruction to the Company, unless the Company
directs the Trustee to deliver 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 Securityholder has converted
pursuant to Article 11.

SECTION 2.12.  DEFAULTED INTEREST

     If the Company defaults in a payment of interest on the Securities, it
shall pay the defaulted interest in any lawful manner not inconsistent with the
requirements of any securities exchange on which the Securities are listed. It
may pay the defaulted interest, plus any interest payable on the defaulted
interest, to the Persons who are Securityholders on a subsequent special record
date. The Company shall fix the record date and payment date for the payment of
any defaulted interest. At least 15 days before the record date, the Company
shall mail to each Securityholder and the Trustee 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 "CUSIP" numbers (if then
generally in use), and, if so, the Trustee shall use "CUSIP" numbers in notices
of redemption as a convenience to Holders; provided that any such notice may
state that no representation is made as to the correctness of such numbers
either as printed on the Securities or as contained in any notice of a
redemption and that reliance may be placed only on the other identification
numbers printed on the Securities, and any such redemption shall not be affected
by any defect in or omission of such numbers. The Company will promptly notify
the Trustee of any change in the CUSIP numbers.

SECTION 2.14.  ADDITIONAL TRANSFER AND EXCHANGE REQUIREMENTS

     (a)  TRANSFER AND EXCHANGE OF GLOBAL SECURITIES

          (1)  Certificated Securities shall be issued in exchange for interests
     in the Global Securities only if (x) the Depositary notifies the Company
     that it is unwilling or unable to continue as depositary for the Global
     Securities or if it at any time ceases to be a "clearing agency" registered
     under the Exchange Act, if so required by applicable law or regulation and
     a successor depositary is not appointed by the Company within 90 days, or
     (y) an Event of Default has occurred and is continuing. In either case, the
     Company shall execute, and the Trustee shall, upon receipt of a Company
     order (which the Company agrees to delivery promptly), authenticate and
     deliver Certificated Securities in an aggregate principal amount equal to
     the principal amount of such Global Securities in exchange therefor. Only
     Restricted Certificated Securities shall be issued in exchange for
     beneficial interests in Restricted Global Securities, and only Unrestricted
     Certificated Securities shall be issued in exchange for beneficial
     interests in Unrestricted Global Securities. Certificated Securities

                                      -12-

<PAGE>

     issued in exchange for beneficial interests in Global Securities shall be
     registered in such names and shall be in such authorized denominations as
     the Depositary, pursuant to instructions from its direct or indirect
     participants or otherwise, shall instruct the Trustee. The Trustee shall
     deliver or cause to be delivered such Certificated Securities to the
     persons in whose names such Securities are so registered. Such exchange
     shall be effected in accordance with the Applicable Procedures.

          (2)  Notwithstanding any other provisions of this Indenture other than
     the provisions set forth in Section 2.14(a)(1), a Global Security may not
     be transferred as a whole except by the Depositary to a nominee of the
     Depositary or by a nominee of the Depositary to the Depositary or another
     nominee of the Depositary or by the Depositary or any such nominee to a
     successor Depositary or a nominee of such successor Depositary.

     (b)  TRANSFER AND EXCHANGE OF CERTIFICATED SECURITIES. In the event that
Certificated Securities are issued in exchange for beneficial interests in
Global Securities in accordance with Section 2.14(a)(1) of this Indenture, on or
after such event when Certificated Securities are presented by a Holder to a
Registrar with a request:

          (x)  to register the transfer of the Certificated Securities to a
     person who will take delivery thereof in the form of Certificated
     Securities only; or

          (y)  to exchange such Certificated Securities for an equal principal
     amount of Certificated Securities of other authorized denominations, such
     Registrar shall register the transfer or make the exchange as requested;

PROVIDED, HOWEVER, that the Certificated Securities presented or surrendered for
register of transfer or exchange:

          (1)  shall be duly endorsed or accompanied by a written instrument of
     transfer in accordance with the proviso to the first paragraph of Section
     2.06(a); and

          (2)  in the case of a Restricted Certificated Security, such request
     shall be accompanied by the following additional information and documents,
     as applicable:

               (i)   if such Restricted Certificated Security is being delivered
          to the Registrar by a Holder for registration in the name of such
          Holder, without transfer, or such Restricted Certificated Security is
          being transferred to the Company or a Subsidiary, a certification to
          that effect from such Holder (in substantially the form set forth in
          the Transfer Certificate);

               (ii)  (x) if such Restricted Certificated Security is being
          transferred to a person the Holder reasonably believes is a QIB in
          accordance with Rule 144A or pursuant to an effective registration
          statement or (y) if such Restricted Certificated Security is being
          transferred to a non-U.S. person in an

                                      -13-

<PAGE>

          offshore transaction in accordance with Rule 903 or Rule 904, under
          the Securities Act, a certification to that effect from such Holder
          (in substantially the form set forth in the Transfer Certificate); or

               (iii) if such Restricted Certificated Security is being
          transferred (i) pursuant to an exemption from the registration
          requirements of the Securities Act in accordance with Rule 144 or (ii)
          pursuant to an exemption from the registration requirements of the
          Securities Act (other than pursuant to Rule 144A or Rule 144) and as a
          result of which, in the case of a Security transferred pursuant to
          this clause (ii), such Security shall cease to be a "restricted
          security" within the meaning of Rule 144, a certification to that
          effect from the Holder (in substantially the form set forth in the
          Transfer Certificate) and, if the Company or such Registrar so
          requests, a customary opinion of counsel, certificates and other
          information reasonably acceptable to the Company and such Registrar to
          the effect that such transfer is in compliance with the registration
          requirements of the Securities Act.

     (c)  TRANSFER OF A BENEFICIAL INTEREST IN A RESTRICTED GLOBAL SECURITY FOR
A BENEFICIAL INTEREST IN AN UNRESTRICTED GLOBAL SECURITY. Any person having a
beneficial interest in a Restricted Global Security may upon request, subject to
the Applicable Procedures, transfer such beneficial interest to a person who is
required or permitted to take delivery thereof in the form of an Unrestricted
Global Security. Upon receipt by the Trustee of written instructions, or such
other form of instructions as is customary for the Depositary, from the
Depositary or its nominee on behalf of any person having a beneficial interest
in a Restricted Global Security and the following additional information and
documents in such form as is customary for the Depositary from the Depositary or
its nominee on behalf of the person having such beneficial interest in the
Restricted Global Security (all of which may be submitted by facsimile or
electronically):

          (1)  if such beneficial interest is being transferred pursuant to an
     effective registration statement under the Securities Act, a certification
     to that effect from the transferor (in substantially the form set forth in
     the Transfer Certificate); or

          (2)  if such beneficial interest is being transferred (i) pursuant to
     an exemption from the registration requirements of the Securities Act in
     accordance with Rule 144 or (ii) pursuant to an exemption from the
     registration requirements of the Securities Act (other than pursuant to
     Rule 144A or Rule 144) and as a result of which, in the case of a Security
     transferred pursuant to this clause (ii), such Security shall cease to be a
     "restricted security" within the meaning of Rule 144, a certification to
     that effect from the transferor (in substantially the form set forth in the
     Transfer Certificate) and, if the Company or the Trustee so requests, a
     customary opinion of counsel, certificates and other information reasonably
     acceptable to the Company and the Trustee to the effect that such transfer
     is in compliance with the registration requirements of the Securities Act,
     the Trustee, as a Registrar and Securities

                                      -14-

<PAGE>

     Custodian, shall reduce or cause to be reduced the aggregate principal
     amount of the Restricted Global Security by the appropriate principal
     amount and shall increase or cause to be increased the aggregate principal
     amount of the Unrestricted Global Security by a like principal amount. Such
     transfer shall otherwise be effected in accordance with the Applicable
     Procedures. If no Unrestricted Global Security is then outstanding, the
     Company shall execute and the Trustee shall, upon receipt of a Company
     Order (which the Company agrees to deliver promptly), authenticate and
     deliver an Unrestricted Global Security.

     (d)  TRANSFER OF A BENEFICIAL INTEREST IN AN UNRESTRICTED GLOBAL SECURITY
FOR A BENEFICIAL INTEREST IN A RESTRICTED GLOBAL SECURITY. Any person having a
beneficial interest in an Unrestricted Global Security may upon request, subject
to the Applicable Procedures, transfer such beneficial interest to a person who
is required or permitted to take delivery thereof in the form of a Restricted
Global Security (it being understood that only QIBs or a person acquiring
Securities pursuant to the exemption provided under Regulation S under the
Securities Act may own beneficial interests in Restricted Global Securities).
Upon receipt by the Trustee of written instructions or such other form of
instructions as is customary for the Depositary, from the Depositary or its
nominee, on behalf of any person having a beneficial interest in an Unrestricted
Global Security and, in such form as is customary for the Depositary, from the
Depositary or its nominee on behalf of the person having such beneficial
interest in the Unrestricted Global Security (all of which may be submitted by
facsimile or electronically) a certification from the transferor (in
substantially the form set forth in the Transfer Certificate) to the effect that
such beneficial interest is being transferred to a person that the transferor
reasonably believes is a QIB in accordance with Rule 144A or is being
transferred to a non U.S. person in an offshore transaction in accordance with
Rule 903 or 904, under the Securities Act. The Trustee, as a Registrar and
Securities Custodian, shall reduce or cause to be reduced the aggregate
principal amount of the Unrestricted Global Security by the appropriate
principal amount and shall increase or cause to be increased the aggregate
principal amount of the Restricted Global Security by a like principal amount.
Such transfer shall otherwise be effected in accordance with the Applicable
Procedures. If no Restricted Global Security is then outstanding, the Company
shall execute and the Trustee shall, upon receipt of a Company Order (which the
Company agrees to deliver promptly), authenticate and deliver a Restricted
Global Security.

     (e)  TRANSFERS OF CERTIFICATED SECURITIES FOR BENEFICIAL INTEREST IN GLOBAL
SECURITIES. In the event that Certificated Securities are issued in exchange for
beneficial interests in Global Securities and, thereafter, the events or
conditions specified in Section 2.14(a)(1) which required such exchange shall
cease to exist, the Company shall mail notice to the Trustee and to the Holders
stating that Holders may exchange Certificated Securities for interests in
Global Securities by complying with the procedures set forth in this Indenture
and briefly describing such procedures and the events or circumstances requiring
that such notice be given. Thereafter, if Certificated Securities are presented
by a Holder to a Registrar with a request:

                                      -15-

<PAGE>

               (x)   to register the transfer of such Certificated Securities to
          a person who will take delivery thereof in the form of a beneficial
          interest in a Global Security, which request shall specify whether
          such Global Security will be a Restricted Global Security or an
          Unrestricted Global Security; or

               (y)   to exchange such Certificated Securities for an equal
          principal amount of beneficial interests in a Global Security, which
          beneficial interests will be owned by the Holder transferring such
          Certificated Securities (provided that in the case of such an
          exchange, Restricted Certificated Securities may be exchanged only for
          Restricted Global Securities and Unrestricted Certificated Securities
          may be exchanged only for Unrestricted Global Securities), the
          Registrar shall register the transfer or make the exchange as
          requested by canceling such Certificated Security and causing, or
          directing the Securities Custodian to cause, the aggregate principal
          amount of the applicable Global Security to be increased accordingly
          and, if no such Global Security is then outstanding, the Company shall
          issue and the Trustee shall authenticate and deliver a new Global
          Security;

PROVIDED, HOWEVER, that the Certificated Securities presented or surrendered for
registration of transfer or exchange:

          (1)  shall be duly endorsed or accompanied by a written instrument of
     transfer in accordance with the proviso to the first paragraph of Section
     2.06(a);

          (2)  in the case of a Restricted Certificated Security to be
     transferred for a beneficial interest in an Unrestricted Global Security,
     such request shall be accompanied by the following additional information
     and documents, as applicable:

               (i)   if such Restricted Certificated Security is being
          transferred pursuant to an effective registration statement under the
          Securities Act, a certification to that effect from such Holder (in
          substantially the form set forth in the Transfer Certificate); or

               (ii)  if such Restricted Certificated Security is being
          transferred pursuant to (i) an exemption from the registration
          requirements of the Securities Act in accordance with Rule 144 or (ii)
          pursuant to an exemption from the registration requirements of the
          Securities Act (other than pursuant to Rule 144A or Rule 144) and as a
          result of which, in the case of a Security transferred pursuant to
          this clause (ii), such Security shall cease to be a "restricted
          security" within the meaning of Rule 144, a certification to that
          effect from such Holder (in substantially the form set forth in the
          Transfer Certificate), and, if the Company or the Registrar so
          requests, a customary opinion of counsel, certificates and other
          information reasonably acceptable to the Company and the Trustee to
          the effect that such transfer is in compliance with the registration
          requirements of the Securities Act;

                                      -16-

<PAGE>

          (3)  in the case of a Restricted Certificated Security to be
     transferred or exchanged for a beneficial interest in a Restricted Global
     Security, such request shall be accompanied by a certification from such
     Holder (in substantially the form set forth in the Transfer Certificate) to
     the effect that such Restricted Certificated Security is being transferred
     to a person the Holder reasonably believes is a QIB (which, in the case of
     an exchange, shall be such Holder) in accordance with Rule 144A or is being
     transferred to a non U.S. person in an offshore transaction in accordance
     with Rule 903 or 904, under the Securities Act;

          (4)  in the case of an Unrestricted Certificated Security to be
     transferred or exchanged for a beneficial interest in an Unrestricted
     Global Security, such request need not be accompanied by any additional
     information or documents; and

          (5)  in the case of an Unrestricted Certificated Security to be
     transferred or exchanged for a beneficial interest in a Restricted Global
     Security, such request shall be accompanied by a certification from such
     Holder (in substantially the form set forth in the Transfer Certificate) to
     the effect that such Unrestricted Certificated Security is being
     transferred to a person the Holder reasonably believes is a QIB (which, in
     the case of an exchange, shall be such Holder) in accordance with Rule 144A
     or is being transferred to a non U.S. person in an offshore transaction in
     accordance with Rule 903 or 904, under the Securities Act.

     (f)  LEGENDS

          (1)  Except as permitted by the following paragraphs (2) and (3), each
     Global Security and Certificated Security (and all Securities issued in
     exchange therefor or upon registration of transfer or replacement thereof)
     shall bear a legend in substantially the form called for by footnote 2 to
     EXHIBIT A hereto (each a "Transfer Restricted Security" for so long as it
     is required by this Indenture to bear such legend). Each Transfer
     Restricted Security shall have attached thereto a certificate (a "Transfer
     Certificate") in substantially the form called for by footnote 5 to EXHIBIT
     A hereto.

          (2)  Upon any sale or transfer of a Transfer Restricted Security (w)
     after the expiration of the holding period applicable to sales of the
     Securities under Rule 144(k) of the Securities Act, (x) pursuant to Rule
     144, (y) pursuant to an effective registration statement under the
     Securities Act or (z) pursuant to any other available exemption (other than
     Rule 144A) from the registration requirements of the Securities Act and as
     a result of which, in the case of a Security transferred pursuant to this
     clause (z), such Security shall cease to be a "restricted security" within
     the meaning of Rule 144:

               (i)   in the case of any Restricted Certificated Security, any
          Registrar shall permit the Holder thereof to exchange such Restricted
          Certificated Security for an Unrestricted Certificated Security, or
          (under the circumstances described in Section 2.14(e)) to transfer
          such Restricted

                                      -17-

<PAGE>

          Certificated Security to a transferee who shall take such Security in
          the form of a beneficial interest in an Unrestricted Global Security,
          and in each case shall rescind any restriction on the transfer of such
          Security; PROVIDED, HOWEVER, that the Holder of such Restricted
          Certificated Security shall, in connection with such exchange or
          transfer, comply with the other applicable provisions of this Section
          2.14; and

               (ii)  in the case of any beneficial interest in a Restricted
          Global Security, the Trustee shall permit the beneficial owner thereof
          to transfer such beneficial interest to a transferee who shall take
          such interest in the form of a beneficial interest in an Unrestricted
          Global Security and shall rescind any restriction on transfer of such
          beneficial interest; PROVIDED, that such Unrestricted Global Security
          shall continue to be subject to the provisions of Section 2.14(a)(2);
          and PROVIDED, FURTHER, that the owner of such beneficial interest
          shall, in connection with such transfer, comply with the other
          applicable provisions of this Section 2.14.

          (3)  Upon the exchange, registration of transfer or replacement of
     Securities not bearing the legend described in paragraph (1) above, the
     Company shall execute, and the Trustee shall authenticate and deliver
     Securities that do not bear such legend and that do not have a Transfer
     Certificate attached thereto.

          (4)  After the expiration of the holding period pursuant to Rule
     144(k) of the Securities Act, the Company may with the consent of the
     Holder of a Restricted Global Security or Restricted Certificated Security,
     remove any restriction of transfer on such Security, and the Company shall
     execute, and the Trustee shall authenticate and deliver Securities that do
     not bear such legend and that do not have a Transfer Certificate attached
     thereto.

                                   ARTICLE 3.

                                   REDEMPTION

SECTION 3.01.  OPTIONAL REDEMPTION; NOTICE TO TRUSTEE

     The Securities may not be redeemed prior to July 5, 2010 and are redeemable
on such date and thereafter at the option of the Company, in accordance with
this Article 3 and paragraph 5 of the Securities, as a whole at any time, or in
part from time to time, at 100% of the principal amount, plus accrued and unpaid
interest up to, but not including, the redemption date. Subject to Section 3.03,
in case of any redemption at the elected of the Company of any of the
Securities, the Company shall, at least 45 days prior to the redemption date
fixed by the Company (unless a shorter notice shall be satisfactory to the
Trustee), notify the Trustee in writing of such redemption date.

                                      -18-

<PAGE>

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 by lot, or in its discretion, on a pro rata
basis from Securities outstanding and not previously called for redemption
(unless the Company specifically directs the Trustee otherwise), in such manner
as the Trustee shall deem fair and appropriate. The Trustee shall make the
selection (and provide the Company with written notice of such selection) at
least 30 days but not more than 60 days before the redemption date. Securities
and portions of them the Trustee selects for redemption shall be in amounts of
$1,000 or integral multiples of $1,000. In the event that the Trustee is not the
Registrar, the Registrar shall provide to the Trustee such information as the
Trustee may reasonably request to implement the selection. Provisions of this
Indenture that apply to Securities called for redemption also apply to portions
of Securities called for redemption.

SECTION 3.03.  NOTICE OF REDEMPTION.

     At least 20 days but not more than 60 days before a redemption date, the
Company shall mail a notice of redemption to each Holder whose Securities are to
be redeemed at such Holder's address as shown on the register kept by the
Registrar, and to beneficial owners as required by applicable law. The notice
shall identify the Securities (including CUSIP numbers, if any) to be redeemed
and shall state:

     (1)  the redemption date;

     (2)  the redemption price;

     (3)  the conversion price;

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

     (5)  that Securities called for redemption may be converted at any time
before the close of business on the date that is two Trading Days immediately
preceding the redemption date;

     (6)  that Holders who want to convert Securities must satisfy the
requirements set forth in paragraph 8 of the Securities;

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

     (8)  that interest on Securities called for redemption ceases to accrue on
and after the redemption date (unless funds in the requisite amount are not paid
or made available for payment on that date), and the amount of interest accrued
on the Securities called for redemption up to but not including the redemption
date;

                                      -19-

<PAGE>

     (9)  if less than all of any Security is to be redeemed, the principal
amount of such Security to be redeemed;

     (10) the CUSIP number, if any, printed on the Securities being redeemed;
and

     (11) that no representation is made as to the correctness or accuracy of
the CUSIP number, if any, listed in such notice or printed on the Securities.

     If any of the Securities to be redeemed is in the form of a Global
Security, then the Company shall modify such notice to the extent necessary to
accord with the Applicable Procedures. Upon ten days prior notice to the
Trustee, the Company may request that the Trustee mail the notice of redemption
(prepared by the Company) in the Company's name and at its expense.

SECTION 3.04.  EFFECT OF NOTICE OF REDEMPTION

     Once notice of redemption is mailed, Securities called for redemption,
unless theretofore converted into Common Stock pursuant to the terms of this
Indenture, shall become due and payable on the redemption date at the redemption
price. Upon surrender to the Paying Agent, such Securities shall be paid at the
redemption price, plus accrued interest to the redemption date; PROVIDED,
HOWEVER, that any regular semi-annual payment of interest becoming due on the
redemption date shall be payable to the Holder of any such Security as provided
in paragraph 2 of the Securities.

SECTION 3.05.  DEPOSIT OF REDEMPTION PRICE

     No later than 11:00 a.m. on the redemption date, the Company shall deposit
in immediately available funds with the Paying Agent money sufficient to pay the
redemption price of and interest accrued to the redemption date on all
Securities to be redeemed on that date other than Securities or portions thereof
called for redemption on that date which have been delivered by the Company to
the Trustee for cancellation. The Paying Agent shall return to the Company any
money not required for that purpose because of conversion of Securities.

SECTION 3.06.  SECURITIES REDEEMED IN PART

     Upon surrender to the Trustee 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.

                                      -20-

<PAGE>

                                   ARTICLE 4.

                                   REPURCHASES

SECTION 4.01.  PURCHASE OF SECURITIES AT OPTION OF THE HOLDER

     (a)  Subject to the terms and conditions of this Article, the Company shall
purchase, at the option of the Holder thereof, all or any portion of the
Securities held by such Holder on July 1, 2010, July 1, 2013 and July 1, 2018
(each, a "Purchase Date") at a purchase price per Security equal to 100% of the
aggregate principal amount of the Security (the "Purchase Price"), together with
accrued interest up to but not including the Purchase Date; provided that if the
Purchase Date is on or after an interest record date but on or prior to the
related interest payment date, interest will be payable to the Holders in whose
names the Securities are registered at the close of business on the relevant
record date.

     Purchases of Securities hereunder shall be made, at the option of the
Holder thereof, upon:

          (1)  delivery to the Paying Agent by the Holder of a written notice of
     purchase (a "Purchase Notice") at any time from the opening of business on
     the date that is 20 Business Days prior to the Purchase Date until the
     close of business on the fifth Business Day prior to such Purchase Date
     stating:

               (A)  the certificate number of the Security which the Holder will
          deliver to be purchased,

               (B)  the portion of the principal amount of the Security which
          the Holder will deliver to be purchased, which portion must be in
          principal amounts at maturity of $1,000 or an integral multiple
          thereof,

               (C)  that such Security shall be purchased as of the Purchase
          Date pursuant to the terms and conditions specified in paragraph 6 of
          the Securities and in this Indenture, and

               (D)  delivery of such Security to the Paying Agent prior to, on
          or after the Purchase Date (together with all necessary endorsements)
          at the offices of the Paying Agent, such delivery being a condition to
          receipt by the Holder of the Purchase Price therefor, together with
          all accrued interest, shall be so paid pursuant to this Section 4.01
          only if the Security so delivered to the Paying Agent shall conform in
          all respects to the description thereof in the related Purchase
          Notice, as determined by the Company.

                                      -21-

<PAGE>

     The Company shall purchase from the Holder thereof, pursuant to this
Section 4.01, a portion of a Security if the principal amount of such portion is
$1,000 or an integral multiple of $1,000. Provisions of this Indenture that
apply to the purchase of all of a Security also apply to the purchase of such
portion of such Security.

     Any purchase by the Company contemplated pursuant to the provisions of this
Section 4.01 shall be consummated by the delivery of the consideration to be
received by the Holder promptly following the later of the Purchase Date and the
time of delivery of the Security.

     Notwithstanding anything herein to the contrary, any Holder delivering to
the Paying Agent the Purchase Notice contemplated by this Section 4.01 shall
have the right to withdraw such Purchase Notice at any time prior to the close
of business on the second Business Day prior to the Purchase Date by delivery of
a written notice of withdrawal to the Paying Agent in accordance with Section
4.01(e).

     The Paying Agent shall promptly notify the Company of the receipt by it of
any Purchase Notice or written notice of withdrawal thereof.

     (b)  The Purchase Price of Securities in respect of which a Purchase Notice
pursuant to Section 4.01(a) has been given shall be paid in U.S. legal tender
(cash).

     (c)  In connection with any purchase of Securities pursuant to this Section
4.01, the Company shall give written notice of the Purchase Date to the Holders
(the "Company Notice"). The Company Notice shall be sent by first-class mail to
the Trustee and to each Holder (and to each beneficial owner as required by
applicable law) not less than 20 Business Days prior to any Purchase Date (the
"Company Notice Date"). Each Company Notice shall include a form of Purchase
Notice to be completed by a Securityholder and shall state:

          (i)    the Purchase Price and the conversion price;

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

          (iii)  that Securities as to which a Purchase Notice has been given
     may be converted if they are otherwise convertible only in accordance with
     Article 11 hereof and paragraph 8 of the Securities if the applicable
     Purchase Notice has been withdrawn in accordance with the terms of this
     Indenture;

          (iv)   that Securities must be surrendered to the Paying Agent to
     collect payment;

          (v)    that the Purchase Price for, and any accrued interest on, any
     Security as to which a Purchase Notice has been given and not withdrawn
     will be paid promptly following the later of the Purchase Date and the time
     of surrender of such Security as described in subclause (iv) above;

                                      -22-

<PAGE>

          (vi)   the procedures the Holder must follow to exercise rights under
     this Section and a brief description of those rights;

          (vii)  briefly, the conversion rights of the Securities;

          (viii) the procedures for withdrawing a Purchase Notice (including
     pursuant to the terms of Section 4.01(e);

          (ix)   that, unless the Company defaults in making payment on
     Securities for which a Purchase Notice has been submitted, interest on such
     Securities will cease to accrue on the Purchase Date, and

          (x)    the CUSIP number of the Securities.

     If any of the Securities are to be redeemed in the form of a Global
Security, the Company shall modify such notice to the extent necessary to accord
with the Applicable Procedures.

     At the Company's request, the Trustee shall give such Company Notice in the
Company's name and at the Company's expense; provided, however, that, in all
cases, the text of such Company Notice shall be prepared by the Company.

     (d)  The Company shall deposit cash, in respect of purchases under this
Section 4.01, at the time and in the manner as provided in Section 4.01(f),
sufficient to pay the aggregate Purchase Price of all Securities, together with
all accrued interest to, but not including, the Purchase Date, to be purchased
pursuant to this Section 4.01.

     (e)  Upon receipt by the Paying Agent of the Purchase Notice specified in
Section 4.01(a), the Holder of the Security in respect of which such Purchase
Notice was given shall (unless such Purchase Notice is withdrawn as specified in
the following two paragraphs) thereafter be entitled to receive solely the
Purchase Price, together with all accrued interest to, but not including, the
Purchase Date thereon, with respect to such Security. Such Purchase Price,
together with all accrued interest to, but not including, the Purchase Date
thereon, shall be paid to such Holder, subject to receipt of funds by the Paying
Agent, promptly following the later of (x) the Purchase Date with respect to
such Security (provided the conditions in Section 4.01(a) have been satisfied)
and (y) the time of delivery of such Security to the Paying Agent by the Holder
thereof in the manner required by Section 4.01(a). Securities in respect of
which a Purchase Notice has been given by the Holder thereof may not be
converted pursuant to Article 11 hereof on or after the date of the delivery of
such Purchase Notice, unless such Purchase Notice has first been validly
withdrawn as specified in the following two paragraphs.

                                      -23-

<PAGE>

     A Purchase Notice may be withdrawn by means of a written notice of
withdrawal delivered to the office of the Paying Agent in accordance with the
Purchase Notice at any time prior to the close of business on the second
Business Day prior to the Purchase Date specifying:

          (1)  the certificate number, if any, of the Security in respect of
     which such notice of withdrawal is being submitted,

          (2)  the principal amount of the Security with respect to which such
     notice of withdrawal is being submitted, and

          (3)  the principal amount, if any, of such Security which remains
     subject to the original Purchase Notice and which has been or will be
     delivered for purchase by the Company.

     A written notice of withdrawal of a Purchase Notice shall be in the form
set forth in the preceding paragraph.

     There shall be no purchase of any Securities pursuant to this Section 4.01
if there has occurred (prior to, on or after as the case may be, the giving, by
the Holders of such Securities, of the required Purchase Notice) and is
continuing an Event of Default (other than a default in the payment of the
Purchase Price with respect to such Securities). The Paying Agent will promptly
return to the respective Holders thereof any Securities (x) with respect to
which a Purchase Notice has been withdrawn in compliance with this Indenture, or
(y) held by it during the continuance of an Event of Default (other than a
default in the payment of the Purchase Price with respect to such Securities) in
which case, upon such return, the Purchase Notice with respect thereto shall be
deemed to have been withdrawn.

     (f)  Prior to 10:00 a.m. (local time in the City of New York) on the
Business Day following the Purchase Date, the Company shall deposit with the
Trustee or with the Paying Agent (or, if the Company or a Subsidiary or an
Affiliate of either of them is acting as the Paying Agent, shall segregate and
hold in trust as provided in Section 2.04(c)) an amount of money (in immediately
available funds if deposited on such Business Day) sufficient to pay the
aggregate Purchase Price of, together with all accrued interest to, but not
including, the Purchase Date on, all the Securities or portions thereof which
are to be purchased as of the Purchase Date.

     (g)  Any Security which is to be repurchased only in part shall be
surrendered to the Trustee (with, if the Company or the Trustee so requires, due
endorsement by, or a written instrument of transfer in form 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 without service charge, a new
Security or Securities, 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.

                                      -24-

<PAGE>

SECTION 4.02.  REPURCHASE UPON FUNDAMENTAL CHANGE

     The Company covenants and agrees that, in the event that there occurs a
Fundamental Change (as defined in Section 4.05(b) hereof), each Holder will have
the right, at such Holder's option, to require the Company to repurchase all, or
any portion that is an integral multiple of $1,000, of such Holder's Securities
on the Fundamental Change Purchase Date (as defined in Section 4.04 below)
selected by the Company as provided below at a repurchase price (the
"Fundamental Change Purchase Price") which is equal to 100% of the principal
amount of such Securities plus accrued interest to the Fundamental Change
Purchase Date.

SECTION 4.03.  NOTICES, ETC.

     Unless the Company shall have theretofore called for redemption all the
outstanding Securities, on or before the 30th day after the occurrence of a
Fundamental Change, the Company shall deliver to the Trustee, and the Company
shall, or, if so requested by the Company upon ten days' prior written notice,
the Trustee shall, in the name of the Company and at its expense, mail to each
Holder at such Holder's address appearing in the Securities Register a written
notice (the "Fundamental Change Company Notice") describing the occurrence of
the Fundamental Change and of the repurchase right set forth herein arising as a
result thereof, as well as stating the final date by which the Securities must
be surrendered for repurchase, the conversion price then in effect, the
Fundamental Change Purchase Date, the Fundamental Change Purchase Price and the
procedure which the Holder must follow to elect repurchase. The Company shall
also cause a copy of such notice of the repurchase right to be published in a
newspaper of general circulation in the Borough of Manhattan, The City of New
York.

     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 Securities is in the form of a Global Security, then the
Company shall modify such notice to the extent necessary to accord with the
Applicable Procedures.

SECTION 4.04.  EXERCISING FUNDAMENTAL CHANGE REPURCHASE RIGHT

     (a)  To elect repurchase of any Securities or portion thereof upon a
Fundamental Change, the Holder will be required to surrender, on or before the
Final Surrender Date (as defined below), (i) in the case of Global Securities,
to the Conversion Agent by book-entry delivery of the interest in the Security
in global form to be repurchased, or (ii) in the case of definitive Securities,
at any place where principal is payable, such Security duly endorsed or assigned
to the Company or in blank, in any event together with written notice of the
Holder's election to have the Company repurchase all or any $1,000 portion of
such Security specified in such notice. Election of repurchase by a Holder shall
be irrevocable (unless the Company defaults in payment of the Fundamental Change
Purchase Price for the Securities on the Fundamental Change Purchase Date) and
the right to convert the Securities as to which such

                                      -25-

<PAGE>

Holder has made such election shall expire when such Securities are so
surrendered (unless the Company defaults in payment of the Fundamental Change
Purchase Price for the Securities on the Fundamental Change Purchase Date and
such election is revoked). "Final Surrender Date" shall mean the date, which is
subject to any contrary requirements of applicable law, 60 days after the date
of mailing of the Company Notice. "Fundamental Change Purchase Date" shall mean
the date selected by the Company for the repurchase of the Securities that is
not less than 10 and not more than 30 days after the Final Surrender Date.

     (b)  In the event a repurchase right shall be exercised in accordance with
the terms hereof, the Company shall pay or cause to be paid the Fundamental
Change Purchase Price in cash to the Holder on the Fundamental Change Purchase
Date; PROVIDED, HOWEVER, that installments of interest that mature on or prior
to the Fundamental Change Purchase Date shall be payable in cash to the Holders
of such Securities, registered as such at the close of business on the relevant
record date specified in the Securities according to the terms and provisions of
Article 2.

     (c)  If any Security surrendered for repurchase shall not be so paid on the
Fundamental Change Purchase Date, the principal amount which is payable at
maturity shall, until the Fundamental Change Purchase Price (as calculated at
the date of payment) is paid, continue to bear interest from the Fundamental
Change Purchase Date at the rate borne by the Security and each such Security
shall continue to remain convertible into Common Stock until said Fundamental
Change Purchase Price shall have been paid to the Holder or duly provided for by
deposit with the Paying Agent in immediately available funds without
restriction.

     (d)  Any Security which is to be repurchased only in part shall be
surrendered to the Trustee (with, if the Company or the Trustee so requires, due
endorsement by, or a written instrument of transfer in form 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 without service charge, a new
Security or Securities, 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.

SECTION 4.05.  CERTAIN DEFINITIONS

     For purposes of this Article:

     (a)  The term "Capital Stock" shall mean capital stock of the Company that
does not rank prior, as to the payment of dividends or as to the distribution of
assets upon any voluntary or involuntary liquidation, dissolution or winding up
of the Company, to shares of capital stock of any other class of the Company;

                                      -26-

<PAGE>

     (b)  The term "Fundamental Change" shall mean any of the following:

          (1)  a "person" or "group" (within the meaning of Sections 13(d) and
     14(d)(2) of the Securities Exchange Act of 1934, as amended (the "Exchange
     Act")), becoming the "beneficial owner" (as defined in Rule l3d-3 under the
     Exchange Act) of Voting Shares (as defined below) of the Company entitled
     to exercise more than 50% of the total voting power of all outstanding
     Voting Shares of the Company (including any right to acquire Voting Shares
     that are not then outstanding of which such person or group is deemed the
     beneficial owner); or

          (2)  a change in the Board of Directors in which the individuals who
     constituted the Board of Directors at the beginning of the two-year period
     immediately preceding such change (together with any other director whose
     election by the Board of Directors or whose nomination for election by the
     stockholders of the Company was approved by a vote of at least two-thirds
     of the directors then in office who either were directors at the beginning
     of such period or whose election or nomination for election was previously
     so approved) cease for any reason to constitute a majority of the directors
     then in office; or

          (3)  any consolidation of the Company with, or merger of the Company
     into, any other Person, any merger of another Person into the Company, or
     any sale or transfer of all or substantially all of the assets of the
     Company to another Person (other than (i) a stock-for-stock merger, (ii) a
     merger that does not result in any reclassification, conversion, exchange
     or cancellation of outstanding shares of Common Stock, (iii) a merger that
     is effected solely to change the jurisdiction of incorporation of the
     Company or (iv) any consolidation with or merger of the Company into a
     wholly-owned Subsidiary, or any sale or transfer by the Company of all or
     substantially all of its assets to one or more of its wholly-owned
     Subsidiaries, in any one transaction or a series of transactions, provided,
     in any such case, that the resulting corporation or each such subsidiary
     assumes or guarantees the Company's obligations under the Securities);

     PROVIDED, HOWEVER, that a Fundamental Change shall not occur with respect
     to any such transaction if either (x) the last sale price of the Common
     Stock for any five Trading Days during the ten Trading Days immediately
     preceding the public announcement by the Company of such transaction is at
     least equal to 105% of the conversion price in effect on such Trading Day
     or (y) the consideration in such transaction to the holders of Common Stock
     consists of cash, securities that are, or immediately upon issuance will
     be, listed on a national securities exchange or quoted on The Nasdaq
     National Market, or a combination of cash and such securities, and the
     aggregate fair market value of such consideration (which, in the case of
     such securities, shall be equal to the average of the last sale prices of
     such securities during the ten consecutive Trading Days commencing with the
     sixth Trading Day following

                                      -27-

<PAGE>

     consummation of the transaction) is at least 105% of the conversion price
     in effect on the date immediately preceding the closing date of such
     transaction;

     (c)  The term "Person" shall include any syndicate or group which would be
deemed to be a "person" under Section 13(d)(3) of the Exchange Act as in effect
on the date of the original execution of this Indenture; and

     (d)  The term "Voting Shares" shall mean all outstanding shares of any
class or series (however designated) of Capital Stock entitled to vote generally
in the election of members of the Board of Directors.

                                   ARTICLE 5.

                                   COVENANTS

SECTION 5.01.  PAYMENT OF SECURITIES

     The Company shall pay the principal of and premium, if any, and interest
on, and Purchase Price and Fundamental Change Purchase Price, if any, of the
Securities on the dates and in the manner provided in the Securities and this
Indenture. Principal, premium, if any, Purchase Price and Fundamental Change
Purchase Price, if any, and interest shall be considered paid on the date due if
the Paying Agent (other than the Company) holds on that date money sufficient to
pay all principal, premium, if any, and interest then due and that is
immediately available on such date for payment to the Holders and that is not
subject to restriction including, but not limited to, the restrictions set forth
in Article 12 hereof.

     The Company shall pay interest on overdue principal and premium, if any, at
the rate per annum borne by the Securities; it shall pay interest on overdue
installments of interest at the same rate per annum to the extent lawful.

SECTION 5.02.  COMMISSION REPORTS

     The Company shall comply with the provisions of TIA Section 314(a).

SECTION 5.03.  COMPLIANCE CERTIFICATE

     The Company shall deliver to the Trustee within 120 days after the end of
each fiscal year of the Company a brief certificate from the principal executive
officer, principal financial officer or principal accounting officer as to his
or her knowledge of the Company's compliance with all conditions and covenants
under this Indenture, specifying any known Events of Default. For purposes of
this Section 5.03, such compliance shall be determined without regard to any
period of grace or requirement of notice provided under this Indenture. The
first certificate pursuant to this Section shall be for the year ending on
December 31, 2003.

                                      -28-

<PAGE>

SECTION 5.04.  CORPORATE EXISTENCE

     Subject to Article 6, the Company will do or cause to be done all things
necessary to preserve and keep in full force and effect its corporate existence,
rights (charter and statutory) and franchise; PROVIDED, HOWEVER, that the
Company shall not be required to preserve any such right or franchise if the
Board of Directors shall determine that the preservation thereof is no longer
desirable in the conduct of the business of the Company and that the loss
thereof is not disadvantageous in any material respect to the Holders.

SECTION 5.05.  NOTICE OF DEFAULTS

     In the event that the Company becomes aware of an Event of Default
described in Section 7.01(4), the Company will promptly give written notice to
the Trustee of such occurrence, or of the occurrence of an event which, with the
giving of notice or the passage of time, or both, would entitle the holder or
holders of such indebtedness to declare such indebtedness due and payable before
its maturity.

SECTION 5.06.  FURTHER INSTRUMENTS AND ACTS

     Upon request of the Trustee, the Company will execute and deliver such
further instruments and do such further acts as may be reasonably necessary or
proper to carry out more effectively the purposes of this Indenture.

SECTION 5.07.  RESALE OF CERTAIN SECURITIES

     During the period beginning on the last date of original issuance of the
Securities and ending on the date that is two years from such date, the Company
will not, and will use its best efforts not to permit any of its "affiliates"
(as defined under Rule 144 under the Securities Act or any successor provision
thereto) to, resell (x) any Securities which constitute "restricted securities"
under Rule 144 or (y) any securities into which the Securities have been
converted under this Indenture which constitute "restricted securities" under
Rule 144, that in either case have been reacquired by any of them. The Trustee
shall have no responsibility in respect of the Company's performance of its
agreement in the preceding sentence.

SECTION 5.08.  REGISTRATION RIGHTS

     The Company agrees that the Holders (and any Person that has a beneficial
interest in a Security) from time to time of Transfer Restricted Securities are
entitled to the benefits of the Registration Rights Agreement. Pursuant to the
Registration Rights Agreement, the Company will, at its cost, (a) use its best
efforts to file within 90 days after the first date of original issuance of the
Securities a Registration Statement on Form S-3 (a "Shelf Registration
Statement") covering resales of the Securities and the Common Stock issuable
upon the conversion pursuant to Rule 415 under the Securities Act, (b) use its
best efforts to cause the Shelf Registration Statement to be declared effective
under the Securities Act no

                                      -29-

<PAGE>

later than 180 days after the first date of original issuance of the Securities
and (c) use its best efforts to keep the Shelf Registration Statement effective
after its effective date until the date which is the earliest of (i) the second
anniversary of the effective date of the Shelf Registration Statement, (ii) such
time as all the Securities or Common Stock issuable upon conversion thereof (the
"Registrable Securities") have been sold pursuant to the Shelf Registration
Statement, transferred pursuant to Rule 144 under the Securities Act or
otherwise transferred in a manner that results in such securities not being
subject to transfer restrictions under the Securities Act and the absence of a
need for a restrictive legend regarding registration under the Securities Act,
and (iii) such time as all of the Registrable Securities held by non-affiliates
of the Company are eligible for sale pursuant to Rule 144(k) under the
Securities Act or any successor rule or regulation thereto. Notwithstanding the
foregoing, the Company may suspend the use of the prospectus that is part of the
Shelf Registration Statement for a period not to exceed 45 days in any
three-month period or 90 days in any 12-month period, if the Company determines
in good faith that it is in its best interest to suspend such use of the
prospectus and provides the Holders with written notice of such suspension. The
Company will, in the event a Shelf Registration Statement is filed, among other
things, provide to each Holder named in such Shelf Registration Statement copies
of the prospectus which is a part of the Shelf Registration Statement, notify
each such Holder when the Shelf Registration Statement has become effective and
take certain other actions as are required to permit unrestricted resales of the
Securities and the Common Stock issuable upon the conversion thereof by such
Holders to third parties.

     If (i) on or prior to the 90th day after the first date of original
issuance of the Securities, the Shelf Registration Statement has not been filed
with the Commission; (ii) on or prior to the 180th day after the first date of
original issuance of the Securities, the Shelf Registration Statement has not
been declared effective by the Commission; or (iii) after the Shelf Registration
Statement has been declared effective, such Shelf Registration Statement ceases
to be effective or usable (subject to certain exceptions described in the
Registration Rights Agreement) in connection with resales of Securities and the
Common Stock issuable upon the conversion thereof in accordance with and during
the periods specified in the Registration Rights Agreement (each such event
referred to in clauses (i) through (iii), a "Registration Default"), additional
interest will accrue on the Securities over and above the rate set forth in the
title of the Securities, from and including the date on which any such
Registration Default shall occur to but excluding the date on which all
Registration Defaults have been cured, at the rate of 0.25% per annum until and
including the 90/th/ day after the Registration Default, and at a rate of 0.5%
per annum from and after the 91/st/ day after the Registration Default. In no
event shall the Company be required to pay additional interest in excess of the
applicable maximum amount of 0.5% per annum set forth above regardless of
whether one or multiple Registration Defaults exist. The Company will have no
other liabilities for monetary damages with respect to its registration
obligations; PROVIDED, HOWEVER, that in the event the Company breaches, fails to
comply with or violates certain provisions of the Registration Rights Agreement,
the Holders shall be entitled to, and the Company shall not oppose the granting
of, equitable relief, including injunction and specific performance.

                                      -30-

<PAGE>

     The above description of certain provisions of the Registration Rights
Agreement is qualified by reference to, and is subject in its entirety to, the
more complete description thereof contained in the Registration Rights
Agreement.

                                   ARTICLE 6.

                                   SUCCESSORS

SECTION 6.01.  WHEN COMPANY MAY MERGE, ETC.

     The Company shall not consolidate or merge with or into, or sell, lease,
convey or otherwise dispose of all or substantially all of its assets to, any
Person unless:

     (1)  the Company is the surviving person or that Person is a corporation
organized under the laws of the United States, any state thereof or the District
of Columbia or a corporation or comparable legal entity organized under the laws
of a foreign jurisdiction and whose equity securities are listed on a national
securities exchange in the United States or authorized for quotation on The
Nasdaq National Market;

     (2)  that Person assumes by supplemental indenture executed and delivered
to the Trustee, in form satisfactory to the Trustee, all the obligations of the
Company under the Securities and this Indenture, except that it need not assume
the obligations of the Company as to conversion of Securities if pursuant to
Section 11.17 the Company or another Person enters into a supplemental indenture
obligating it to deliver securities, cash or other assets upon conversion of
Securities;

     (3)  immediately after giving effect to such transaction, no Event of
Default shall have occurred and be continuing; and

     (4)  the Company has delivered to the Trustee an Officers' Certificate and
an Opinion of Counsel, each stating that such consolidation, merger, transfer or
lease and such supplemental indenture comply with this Article and that all
conditions precedent herein provided for related to such transaction have been
complied with.

     The surviving, transferee or lessee corporation shall be the successor
Company, but the predecessor Company in the case of a transfer or lease shall
not be released from the obligation to pay the principal amount or Purchase
Price or Fundamental Change Purchase Price of and premium, if any, and interest
on the Securities.

                                      -31-

<PAGE>

                                   ARTICLE 7.

                              DEFAULTS AND REMEDIES

SECTION 7.01.  EVENTS OF DEFAULT

     An "Event of Default" occurs if:

     (1)  the Company defaults in the payment of interest on any Security when
the same becomes due and payable and the Default continues uncured for a period
of 30 days, whether or not such payment is prohibited or restricted by the
provisions of Article 12;

     (2)  the Company defaults in the payment of (A) principal of or premium, if
any, on any Security when the same becomes due and payable, whether at maturity,
upon redemption or otherwise, or (B) the Purchase Price or Fundamental Change
Purchase Price in respect of any Security when due, in either case whether or
not such payment is prohibited or restricted by the provisions of Article 12;

     (3)  the Company defaults in the performance of any other covenants or
agreements in this Indenture and such default continues for the period and after
the notice specified below;

     (4)  the Company defaults in the payment when due, including any applicable
grace period, in respect of indebtedness for borrowed money of the Company,
which payment is in an amount in excess of $20,000,000, or the Company defaults
with respect to any indebtedness for borrowed money of the Company, which
default results in acceleration of any such indebtedness which is in an amount
of in excess of $20,000,000;

     (5)  the Company pursuant to or within the meaning of any Bankruptcy Law
(as defined below):

          (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 (as defined below) of
     it or for all or substantially all of its property; or

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

                                      -32-

<PAGE>

     (6)  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 or for all or substantially
     all of its property, and the order or decree remains unstayed and in effect
     for 90 consecutive days; 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.

     A Default under clause (3) above is not an Event of Default until the
Trustee or, subject to Section 2.09, the Holders of at least 25% in aggregate
principal amount of the Securities notify the Company in writing of the Default
and the Company does not cure the Default within 60 days after receipt of the
notice. The notice must specify the Default, demand that it be remedied and
state that the notice is a "Notice of Default". When a Default is cured, it
ceases to exist.

SECTION 7.02.  ACCELERATION

     If any Event of Default described in Section 7.01(1) through (4) occurs and
is continuing, the Trustee, by written notice to the Company, or, subject to
Section 2.09, the Holders of at least 25% in aggregate principal amount of the
outstanding Securities, by written notice to the Company and the Trustee, may
declare the principal of and accrued interest on all Securities to be due and
payable. Upon such declaration such principal and interest shall be due and
payable immediately. If any Event of Default described in Section 7.01(5) or (6)
occurs the principal of and accrued interest on all Securities shall
automatically become due and payable, without any action required of the Trustee
or the Holders. The Holders of a majority in principal amount of the Securities
by notice to the Trustee may rescind an acceleration and its consequences if all
existing Events of Default have been cured or waived except nonpayment of
principal or interest that has become due solely because of the acceleration, if
the rescission would not conflict with any judgment or decree of a court of
competent jurisdiction, and if all payments (including fees and expenses) due to
the Trustee have been paid.

                                      -33-

<PAGE>

SECTION 7.03.  OTHER REMEDIES

     If an Event of Default occurs and is continuing, the Trustee may pursue any
available remedy to collect the payment of principal or the Purchase Price or
Fundamental Change Purchase Price of or premium, if any, or 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 the Trustee 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 Securityholder 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. To the extent
permitted by law. No remedy is exclusive of any other remedy and all remedies
are cumulative.

SECTION 7.04.  WAIVER OF PAST DEFAULTS

     Subject to Section 2.09, the Holders of a majority in aggregate principal
amount of the Securities by written notice to the Trustee may waive an existing
Default and its consequences except a Default in the payment of the principal of
or premium, if any, or interest on any Security or a Default under Article 11.
When a Default is waived, it is cured and ceases to exist. This Section 7.04
shall be in lieu of TIA Section 316(a)(1)(B), and TIA Section 316(a)(1)(B) is
hereby expressly excluded from this Indenture and Section, as permitted by the
TIA.

SECTION 7.05.  CONTROL BY MAJORITY

     Subject to Section 2.09, the Holders of a majority in aggregate principal
amount of the Securities 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 another Securityholder, or would expose the Trustee to liability or expense
for which it has not been offered reasonably satisfactory indemnity. This
Section 7.05 shall be in lieu of TIA Section 316(a)(1)(A), and TIA
Section 316(a)(1)(A) is hereby expressly excluded from this Indenture and
Section, as permitted by the TIA.

SECTION 7.06.  LIMITATION ON SUITS

     A Securityholder may pursue any 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 principal amount of the Securities make
a written request to the Trustee to pursue the remedy;

                                      -34-

<PAGE>

     (3)  such Holder or Holders offer to the Trustee indemnity satisfactory to
the Trustee against any loss, liability or expense to be, or which may be,
incurred by the Trustee in pursuing the remedy;

     (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 principal
amount of the Securities do not give the Trustee a direction inconsistent with
the request.

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

SECTION 7.07.  RIGHTS OF HOLDERS TO RECEIVE PAYMENT

     Notwithstanding any other provision of this Indenture, the right of any
Holder to receive payment of the principal of and premium, if any, and interest
on the Security on or after the respective due dates expressed in the Security,
and to convert such Security in accordance with Article 11, or to bring suit for
the enforcement of any such payment on or after such respective due dates and
such right to convert, is absolute and unconditional and shall not be impaired
or affected without the consent of the Holder.

SECTION 7.08.  COLLECTION SUIT BY TRUSTEE

     If an Event of Default specified in Section 7.01(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, premium,
if any, Purchase Price or Fundamental Change Purchase Price, if any, and
interest remaining unpaid together with interest on overdue principal and
premium, if any, and on the principal amount of any Security for which the
Purchase Price or Fundamental Change Purchase Price is overdue, and, to the
extent that payment of such interest is lawful, interest on overdue installments
of interest, in each case at the rate per annum set forth in the title of the
Securities.

SECTION 7.09.  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 and the
Securityholders allowed in any judicial proceeding 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 Securityholder 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 Securityholder in any such proceedings.

                                      -35-

<PAGE>

SECTION 7.10.  PRIORITIES

     If the Trustee collects any money or property pursuant to this Article 7,
it shall pay out the money or property in the following order:

          First: to the Trustee for amounts due under Section 8.07 or any other
          provision of this Indenture;

          Second: to holders of Senior Indebtedness to the extent required by
          Article 12;

          Third: to Securityholders for amounts due and unpaid on the Securities
          for principal, premium, if any, Purchase Price or Fundamental Change
          Purchase Price, 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, Purchase Price or
          Fundamental Change Purchase Price, if any, and interest, respectively;
          and

          Fourth:  to the Company.

     The Trustee may fix a record date and payment date for any payment to
Securityholders pursuant to this Section 7.10.

SECTION 7.11.  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 require the filing by any party litigant
in the suit 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 does
not apply to a suit by the Trustee, a suit by a Holder pursuant to Section 7.07,
or a suit by a Holder or Holders of more than 10% in aggregate principal amount
of the Securities then outstanding.

                                      -36-

<PAGE>

                                   ARTICLE 8.

                                     TRUSTEE

SECTION 8.01.  DUTIES OF TRUSTEE

     (a)  If to the knowledge of the Trustee 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 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. However,
     the Trustee shall examine the certificates and opinions to determine
     whether or not they conform to the requirements of this Indenture, but need
     not verify the accuracy of the contents thereof.

     (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;

          (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;

          (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 7.05; and

          (4)  no provision of this Indenture shall require the Trustee to
     expend or risk its own funds or otherwise incur any financial liability in
     the performance of any of its duties hereunder, or in the exercise of any
     of its rights or powers, if it shall have reasonable grounds for believing
     that repayment of such funds or adequate indemnity against such risk or
     liability is not reasonably assured to it.

     (d)  Every provision of this Indenture that in any way relates to the
Trustee is subject to paragraphs (a), (b) and (c) of this Section.

                                      -37-

<PAGE>

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

SECTION 8.02.  RIGHTS OF TRUSTEE

     Subject to Section 8.01:

     (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;

     (b)  before the Trustee acts or refrains from acting, it may require an
Officers' Certificate 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)  the Trustee may act through agents and shall not be responsible for
the misconduct or negligence of any agent appointed with due care;

     (d)  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 rights or
powers;

     (e)  the Trustee may consult with counsel reasonably acceptable to the
Trustee, which may be counsel to the Company, and the advice of such counsel as
to matters of law shall be full and complete authorization and protection in
respect of any action taken, omitted or suffered by it hereunder in good faith
and in accordance with the advice or opinion of such counsel;

     (f)  the Trustee shall not be bound to ascertain or inquire as to the
performance or observance of any covenants, conditions or agreements on the part
of the Company under this Indenture; but the Trustee may require of the Company
full information and advice as to the performance of the covenants, conditions
and agreements aforesaid; and

     (g)  the Trustee shall not be required to give any bond or surety in
respect of the execution of its trusts and powers or in respect of this
Indenture.

SECTION 8.03.  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
with the same rights the Trustee would have if it were not Trustee. Any Agent
may do the same with like rights.

                                      -38-

<PAGE>

SECTION 8.04.  TRUSTEE'S DISCLAIMER

     The Trustee makes no representation as to the validity or adequacy of this
Indenture or the Securities, shall not be accountable for the Company's use of
the proceeds from the sale of the Securities or the use or application of any
money received by any Paying Agent other than the Trustee, and shall not be
responsible for any statement in the Securities other than the Trustee's
certificate of authentication.

SECTION 8.05.  NOTICE OF DEFAULTS

     If a Default occurs and is continuing and if it is known to the Trustee,
the Trustee shall mail to each Securityholder, at the name and address that
appear in the Securities Register, a notice of the Default within 90 days after
the Default occurs. Except in the case of a Default in payment of the principal
of or premium, if any, or interest on any Security, the Trustee may withhold the
notice if and so long as its board of directors, the executive committee, or a
trust committee of its directors and/or responsible officers in good faith
determines that withholding the notice is in the interests of Securityholders.
The Trustee shall not be deemed to have notice of any Default or Event of
Default other than as described in clauses (1) or (2) of Section 7.01 unless it
shall have received written notice thereof from the Company or any
Securityholder, or a Trust Officer has actual knowledge thereof. The foregoing
sentence of this Section 8.05 shall be in lieu of the proviso to TIA Section
315(b), and such proviso to TIA Section 315(b) is hereby expressly excluded from
this Indenture and Section, as permitted by the TIA.

SECTION 8.06.  REPORTS BY TRUSTEE TO HOLDERS

     If required by TIA Section 313(a), within 60 days after each June 1
beginning with the June 1 following the date of this Indenture, the Trustee
shall mail to each Securityholder a report dated as of such April 1 that
complies with TIA Section 313(a). The Trustee also shall comply with TIA Section
313(b), (c) and (d).

     A copy of each such report at the time of its mailing to Securityholders
shall also be mailed to the Company and shall be filed with the SEC and each
stock exchange, if any, on which the Securities are listed.

     The Company shall promptly notify the Trustee in writing if the Securities
become listed on any stock exchange or of any delisting thereof.

SECTION 8.07.  COMPENSATION AND INDEMNITY

     The Company shall from time to time pay to the Trustee reasonable
compensation for its services. 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, within 45 days after receiving request therefor, for all
reasonable out-of-pocket disbursements, fees and expenses incurred by the
Trustee in connection with the performance of its duties under this Indenture,

                                      -39-

<PAGE>

including without limitation those incurred in connection with the enforcement
of any remedy hereunder or the interpretation of any provision hereunder. Such
expenses may include the reasonable compensation and out-of-pocket expenses of
the Trustee's agents and counsel. All rights, protections and benefits of the
Trustee shall extend to the Trustee acting as Conversion Agent, Paying Agent,
Registrar or other Agent with respect hereto.

     The Company shall indemnify the Trustee for, and hold it harmless against,
any loss or liability incurred by it in connection with this Indenture. The
Trustee shall promptly notify the Company of any claim for which the Trustee may
seek indemnity, including costs and expenses of defending itself against any
claim for liability arising from the exercise or performance of any of its
powers or duties hereunder.

     The Company need not reimburse any expense or indemnify against any loss or
liability incurred by the Trustee through its negligence or bad faith.

     To secure the Company's payment obligations in this Section, 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 principal of,
premium, if any, and interest on particular Securities.

     When the Trustee incurs expenses or renders services after an Event of
Default specified in Section 7.01(5) or (6) occurs, the expenses and the
compensation for such services are intended to constitute expenses of
administration under any Bankruptcy Law.

     Notwithstanding any provision hereof to the contrary, the Trustee's lien
shall not be subordinated to that of Senior Indebtedness.

SECTION 8.08.  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.

     The Trustee may resign by so notifying the Company. The Holders of a
majority in principal amount of the Securities may remove the Trustee by so
notifying the Trustee and the Company. The Company may remove the Trustee if:

     (1)  the Trustee fails to comply with Section 8.10;

     (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.

                                      -40-

<PAGE>

     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 principal amount of the Securities may appoint a successor
Trustee to replace the successor Trustee appointed by the Company.

     If a successor Trustee does not take office within 60 days after the
retiring Trustee resigns or is removed, the retiring Trustee, the Company or the
Holders of at least 10% in principal amount of the Securities may petition any
court of competent jurisdiction for the appointment of a successor Trustee.

     If the Trustee fails to comply with Section 8.10, any Securityholder or
beneficial owner 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 retiring Trustee shall
transfer all property held by it as Trustee to the successor Trustee (subject to
the lien provided for in Section 8.07), 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 Securityholders.

SECTION 8.09.  SUCCESSOR TRUSTEE, AGENTS BY MERGER, ETC.

     If the Trustee or any Agent 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 or Agent, as the case may be.

SECTION 8.10.  ELIGIBILITY; DISQUALIFICATION

     This Indenture shall always have a Trustee who satisfies the requirement of
TIA Sections 310(a)(1) and 310(a)(5). The Trustee (or in the case of a
corporation included in a bank holding company system, the related bank holding
company) shall have a combined capital and surplus of at least $100,000,000 as
set forth in its most recent published annual report of condition. In addition,
if the Trustee is a corporation included in a bank holding company system, the
Trustee, independently of such bank holding company, shall meet the capital
requirements of TIA Section 310(a)(2). The Trustee shall comply with TIA Section
310(b).

                                      -41-

<PAGE>

SECTION 8.11.  PREFERENTIAL COLLECTION OF CLAIMS AGAINST COMPANY

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

                                   ARTICLE 9.

                             DISCHARGE OF INDENTURE

SECTION 9.01.  TERMINATION OF COMPANY'S OBLIGATIONS

     The Company may terminate all of its obligations under this Indenture if:

     (a)  (1)  the Securities mature within one year or all of them are to be
called for redemption (and the Securities are redeemable) within one year and
arrangements satisfactory to the Trustee are made with respect to the giving of
the notice of redemption; and

          (2)  the Company irrevocably deposits in trust with the Trustee money
     or U.S. Government Obligations sufficient to pay, when due, the principal
     of and premium, if any, and interest on the Securities to maturity or
     redemption, as the case may be. The Company may make such deposit only
     during the one-year period referred to in paragraph (1) above and only if
     Article 12 permits it; or

     (b)  all Securities previously authenticated and delivered (other than
destroyed, lost or stolen Securities which have been replaced or paid or
Securities for whose payment money or securities have theretofore been held in
trust and thereafter repaid to the Company, as provided in Section 9.03) have
been delivered to the Trustee for cancellation and the Company has paid all sums
payable by it hereunder.

     However, the obligations in Sections 2.03, 2.04, 2.05, 2.06, 2.07, 2.14,
5.01, 8.07, 8.08, 9.03, 9.04 and 9.05 and in Article 11 shall survive until the
Securities are no longer outstanding. Thereafter the obligations in Sections
8.07, 9.03 and 9.04 shall survive.

     After a termination of the Company's obligations in accordance with this
Section, the Trustee upon request shall acknowledge in writing the discharge of
the Company's obligations under this Indenture except for those surviving
obligations specified above.

     In order to have money available on a payment date to pay principal of and
premium, if any, or interest on the Securities, the U.S. Government Obligations
shall be payable as to principal or interest on or before such payment date in
such amounts as will provide the necessary money.

                                      -42-

<PAGE>

     "U.S. Government Obligations" means direct obligations of the United States
of America for the payment of which the full faith and credit of the United
States of America is pledged and which are not callable at the issuer's option.

SECTION 9.02.  APPLICATION OF TRUST MONEY

     The Trustee shall hold in trust money or U.S. Government Obligations
deposited with it pursuant to Section 9.01. 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 principal of and premium, if
any, and interest on the Securities. Money and securities so held in trust are
not subject to Article 12.

SECTION 9.03.  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.

     Subject to the requirements of applicable law, the Trustee and the Paying
Agent shall pay to the Company upon request any money held by them for the
payment of principal or premium, if any, or interest that remains unclaimed for
two years; PROVIDED, HOWEVER, that, before being required to make any such
repayment, the Trustee or such Paying Agent shall, if the Company so requests
and at the expense of the Company, cause to be published once a week for two
successive weeks, in each case on any day of the week, in an authorized
newspaper in the Borough of Manhattan, The City of New York, or mail to each
such Holder, a notice (in such form as may be deemed appropriate by such Trustee
or Paying Agent) that said monies remain unclaimed and that, after a date named
therein, which shall not be less than 30 days from the date of such publication
or mailing, any unclaimed balance of said monies then remaining will be returned
to the Company. After payment to the Company, Securityholders entitled to the
money must look to the Company for payment as general creditors unless an
applicable abandoned property law designates another Person.

SECTION 9.04.  INDEMNITY FOR GOVERNMENT OBLIGATIONS

     The Company shall pay and shall indemnify the Trustee and each
Securityholder against any tax, fee or other charge imposed on or assessed
against deposited U.S. Government Obligations or the principal and interest
received on such obligations.

SECTION 9.05.  REINSTATEMENT

     If the Trustee is unable to apply any money or United States Government
Obligations in accordance with Section 9.01 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 9.01 until such
time as the Trustee is permitted to apply all such money or United

                                      -43-

<PAGE>

States Government Obligations in accordance with Section 9.01; PROVIDED,
HOWEVER, that if the Company has made any payment of interest on or principal of
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 United States Government Obligations held by the
Trustee.

                                   ARTICLE 10.

                       AMENDMENTS, SUPPLEMENTS AND WAIVERS

SECTION 10.01. WITHOUT CONSENT OF HOLDERS

     The Company and the Trustee may amend or supplement this Indenture or the
Securities without the consent of any Securityholder:

     (1)  to cure any ambiguity, defect or inconsistency herein or in the
Securities;

     (2)  to comply with Section 6.01;

     (3)  to make any change that does not materially adversely affect the
rights of any Securityholder; or

     (4)  to make provision with respect to the conversion rights of Holders
pursuant to the requirements of Section 11.17.

SECTION 10.02. WITH CONSENT OF HOLDERS

     The Company and the Trustee may amend or supplement this Indenture or the
Securities with the written consent of the Holders of at least a majority in
aggregate principal amount of the Securities, and the Holders of a majority in
aggregate principal amount of the Securities may waive compliance by the Company
with any provision of this Indenture or the Securities. However, without the
consent of each Securityholder affected, an amendment, supplement or waiver
under this Section may not:

     (1)  change the stated maturity date of the principal of, or interest on,
any Security or adversely affect the right of a Holder to convert any Security;

     (2)  reduce the principal amount Purchase Price or Fundamental Change
Purchase Price of, or premium, if any, or interest on, any Security;

     (3)  change the currency for payment of principal of, or interest on, any
Security;

     (4)  impair the right to institute suit for the enforcement of any payment
on or with respect to any Security;

                                      -44-

<PAGE>

     (5)  make any change in Article 12 that adversely affects the rights of any
Securityholder;

     (6)  reduce the principal amount of Securities whose Holders must consent
to an amendment or supplement of this Indenture or the waiver of defaults or
compliance hereunder; or

     (7)  make any change in Section 7.04, 7.07 or this 10.02 (second sentence).

     An amendment under this Section may not make any change that adversely
affects the rights under Article 12 of any holder of an issue of Senior
Indebtedness unless the holders of the issue pursuant to its terms consent to
the change.

     It shall not be necessary for the consent of the Holders under this Section
to approve the particular form of any proposed amendment, supplement or waiver,
but it shall be sufficient if such consent approves the substance thereof. The
Company may establish, by delivery of an Officers' Certificate to the Trustee, a
record date for determining Securityholders of record entitled to give any
consent or waiver.

     After an amendment or supplement under this Section becomes effective, the
Company shall mail to Securityholders a notice briefly describing the amendment
or supplement. Any failure of the Company to mail any such notice, or any defect
therein, shall not, however, in any way impair or affect the validity of any
supplemental indenture.

SECTION 10.03. COMPLIANCE WITH TRUST INDENTURE ACT

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

SECTION 10.04. REVOCATION AND EFFECT OF CONSENTS

     Until an amendment, supplement or waiver becomes effective, a consent to it
by a Holder of a Security 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 such Security or portion of a Security if a Trust Officer of
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
Securityholder. Notwithstanding the foregoing, if a record date has been
established for the purpose of determining Securityholders entitled to consent,
such written notice of revocation must be signed by the Securityholder of record
as of the record date or his duly appointed proxy.

                                      -45-

<PAGE>

SECTION 10.05. NOTATION ON OR EXCHANGE OF SECURITIES

     The Trustee may place an appropriate notation relating to an amendment,
supplement or waiver on any Security thereafter authenticated. The Company in
exchange for all Securities may issue, and the Trustee shall authenticate, new
Securities that reflect the amendment, supplement or waiver.

SECTION 10.06. TRUSTEE TO SIGN AMENDMENTS, ETC.

     In executing, or accepting the additional trusts created by, any
supplemental indenture permitted by this Article or Section 11.17 or the
modifications thereby of the trusts created by this Indenture, the Trustee shall
be entitled to receive, and (subject to Section 8.01) shall be fully protected
in relying upon, an Opinion of Counsel and an Officers' Certificate stating that
the execution of such supplemental indenture is authorized or permitted by this
Indenture.

     The Trustee shall sign any amendment or supplement authorized pursuant to
this Article if the amendment or supplement does not adversely affect the rights
of the Trustee. If the amendment or supplement does adversely affect the
Trustee's rights, the Trustee may, but need not, sign it.

                                   ARTICLE 11.

                                   CONVERSION

SECTION 11.01. CONVERSION PRIVILEGE

     Subject to and upon compliance with the provisions of this Article and in
paragraph 8 of the Securities, at the option of the Holder thereof, any Security
may be converted into fully paid and non-assessable shares of Common Stock at
any time on or prior to July 1, 2023, subject in the case of conversion of any
Global Security to any Applicable Procedures. The conversion right with respect
to a Security or the portion thereof that the Company has elected to redeem or
the Holder has elected to have repurchased by the Company in accordance with
Article 4 hereof will terminate on the date (i) that is two Trading Days
immediately preceding the redemption date or the Purchase Date (provided, that
the Holder has withdrawn the Purchase Notice by such date in accordance with
Section 4.01), as the case may be, or (ii) that the Holder has elected to
participate in a repurchase upon a Fundamental Change, unless, in any case, the
Company defaults in making the payment due upon such redemption or repurchase
(in which case the conversion right will terminate at the close of business on
the date such default is cured). The number of shares issuable upon conversion
of a Security is determined by dividing the principal amount to be converted by
the conversion price in effect on the conversion date, and rounding the result
to the nearest 1/l00th of a share, with 500/1,000 of a share to be rounded up.

     The initial conversion price is stated in paragraph 8 of the Securities.
The conversion price is subject to adjustment as provided in this Article 11.

                                      -46-

<PAGE>

SECTION 11.02. CONVERSION PROCEDURE

     To convert a Security, a Holder must satisfy the requirements set forth in
paragraph 8 of the Securities. The first date on which the Holder satisfies all
those requirements in respect of a Security is the conversion date. As soon as
practical on or after the conversion date, the Company shall deliver through the
Conversion Agent a certificate for the number of full shares of Common Stock
issuable upon the conversion of that Security and a check for 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. Anything herein to
the contrary notwithstanding, in the case of Global Securities, conversion
notices may be delivered and such Securities may be surrendered for conversion
in accordance with the Applicable Procedures.

     No payment or adjustment will be made for accrued interest on a converted
Security (other than the payment of interest to the Holder of a Security at the
close of business on a record date pursuant to Section 2.04(b) hereof), or for
dividends or distributions on any Common Stock issued upon conversion of any
Security.

     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.

     If Common Stock is to be issued in the name of a Person other than the
Holder thereof, and the restrictions on transfer of such Security set forth in
the first paragraph of the face of the Security remain in effect, the Holder
must provide certification regarding compliance with the restrictions on
transfer, by executing an assignment in the form attached to the Security.

     Upon surrender of a Security that is converted in part, the Company shall
execute and 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,
the Security may be surrendered to that Conversion Agent on the next succeeding
Business Day with the same force and effect as if surrendered on such last day.

SECTION 11.03. FRACTIONAL SHARES

     The Company will not issue a fractional share of Common Stock upon
conversion of a Security. Instead the Company will deliver to the converting
Securityholder its check for the current market value of the 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, with 0.5 cents to be rounded up.

                                      -47-

<PAGE>

     For purposes of this Section, the current market price of a share of Common
Stock is the Quoted Price of the Common Stock on the last Trading Day prior to
the conversion date.

SECTION 11.04. TAXES ON CONVERSION

     If a Holder of a Security converts it, 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. The Holder shall pay any such tax that is
due because the shares are issued in a name other than such Holder's.

SECTION 11.05. COMPANY TO PROVIDE STOCK

     The Company shall reserve at all times and keep available, free from
preemptive rights, out of its authorized but unissued Common Stock, enough
shares of Common Stock to permit the conversion of the Securities.

     All shares of Common Stock that may be issued upon conversion of the
Securities shall be fully paid and nonassessable.

     The Company shall endeavor to comply with all applicable securities laws
regulating the offer and delivery of shares of Common Stock upon conversion of
Securities and shall endeavor to list such shares on each national securities
exchange on which the Common Stock is listed, or to have such shares approved
for quotation on The Nasdaq National Market or other over-the-counter market on
which the Common Stock is traded.

SECTION 11.06. ADJUSTMENT FOR CHANGE IN CAPITAL STOCK

     If the Company:

     (1)  issues any shares of its capital stock as a dividend (or other
distribution) on the Common Stock;

     (2)  subdivides its outstanding shares of Common Stock into a greater
number of shares of Common Stock;

     (3)  combines its outstanding shares of Common Stock into a smaller number
of shares of Common Stock; or

     (4)  issues by reclassification of its Common Stock any shares of its
capital stock,

then the conversion privilege and the conversion price in effect immediately
prior to such action shall be adjusted so that the Holder of a Security
thereafter converted will receive the number of shares of capital stock of the
Company that would have been received (and if there is more than one class or
series of such capital stock, then shares of each class or series in the same
proportions that would have been received) upon consummation of such action by a
Holder of the number of shares of Common Stock into which such Security might
have been

                                      -48-

<PAGE>

converted immediately prior to such action, with the aggregate conversion price
to be divided evenly among the shares to be issued upon conversion thereof.

     The adjustment described in the preceding paragraph shall become effective
immediately after the record date in the case of a dividend or distribution and
immediately after the effective date in the case of a subdivision, combination
or reclassification.

     If, after an adjustment, a Holder of a Security may receive shares of two
or more classes or series of capital stock of the Company upon conversion of
such Security, the Company shall determine the allocation of the adjusted
conversion price between or among such classes or series of capital stock. After
such allocation, the conversion privilege and the conversion price of each class
of capital stock shall thereafter be subject to adjustment on terms comparable
to those applicable to Common Stock in this Article.

SECTION 11.07. ADJUSTMENT FOR RIGHTS ISSUE

     If the Company distributes any rights or warrants to all holders of its
Common Stock entitling them to subscribe for or purchase shares of Common Stock
at a price per share less than the current market price per share (as defined in
Section 11.11), then, on the Record Date (as defined in this Section 11.07), the
conversion price shall be adjusted in accordance with the formula:

                                    O + (N x P)
                                        -------
                       AC = CC             M
                                    -----------
                       x
                                    O + N

               where:

                      AC  =  the adjusted conversion price.

                      CC  =  the conversion price in effect immediately prior to
                             the close of business on the Record Date.

                      O   =  the number of shares of Common Stock outstanding at
                             the close of business on the Record Date.

                      N   =  the number of additional shares of Common Stock
                             offered.

                      P   =  the offering price per share of the additional
                             shares.

                      M   =  the current market price per share of Common Stock
                             on the Record Date (as defined in this Section
                             11.07).

                                      -49-

<PAGE>

     The adjustment shall become effective immediately after the record date for
the determination of stockholders entitled to receive such rights or warrants
(for purposes of this Section 11.07 only, the "Record Date").

SECTION 11.08. ADJUSTMENT FOR CERTAIN DISTRIBUTIONS

     Subject to the last paragraph of this Section 11.08, if the Company
distributes to all holders of its Common Stock any cash, debt securities (or
other evidences of indebtedness) or other assets (excluding dividends or
distributions for which adjustment is required to be made under Sections 11.06,
11.07 or 11.09), the conversion price shall be reduced in accordance with the
following formula:

                       AC = CC x  M - P
                                ---------
                                    M
               where:

                      AC  =  the adjusted conversion price.

                      CC  =  the conversion price in effect immediately prior to
                             the close of business on the Record Date.

                      M   =  the current market price per share of Common Stock
                             on the Record Date (as defined in this Section
                             11.08).

                      P   =  the aggregate fair market value on the Record Date
                             (as defined in this Section 11.08) (as determined
                             in good faith by the Board of Directors and set
                             forth in a certified resolution filed with the
                             Trustee) of the cash, debt securities (or other
                             evidences of indebtedness) or other assets
                             distributed applicable to one share of Common
                             Stock.

     The adjustment shall become effective immediately after the record date for
the determination of stockholders entitled to receive such distribution (for
purposes of this Section 11.08 only, the "Record Date").

     No adjustment will be made with respect to this Section 11.08 if, in lieu
of such adjustment, the Securityholders, upon conversion, will be entitled to
receive, in addition to the shares of Common Stock into which such Securities
are convertible, the kind and amount of cash, debt securities (or other
evidences of indebtedness) or other assets comprising the distribution that such
Holders would have received had they converted their Securities immediately
prior to the Record Date (as defined in this Section 11.08). In addition, no
adjustment will be made in the event that the then fair market value (as so
determined) of the

                                      -50-

<PAGE>

cash, debt securities (or other evidences of indebtedness) or other assets so
distributed applicable to one share of Common Stock is equal to or greater than
the current market price per share of the Common Stock, in which case, in lieu
of such adjustment, adequate provision shall be made so that each Securityholder
shall have the right to receive upon conversion the amount of cash, debt
securities (or other evidences of indebtedness) or other assets such Holder
would have received had such Holder converted each Security on the Record Date
(as defined in this Section 11.08).

SECTION 11.09. ADJUSTMENT FOR ALL CASH DISTRIBUTION

     Subject to the last two paragraphs of this Section 11.09, if the Company
shall pay or make a dividend or other distribution consisting exclusively of
cash to all holders of its Common Stock, the conversion price shall be reduced
in accordance with the following formula:

                       AC = CC x  M - C
                                ---------
                                    M
               where:

                      AC  =  the adjusted conversion price.

                      CC  =  the conversion price in effect immediately prior to
                             the close of business on the Record Date (as
                             defined in this Section 11.09).

                      M   =  the current market price per share of Common Stock
                             on the Record Date (as defined in this Section
                             11.09).

                      C   =  the amount of cash so distributed and not excluded
                             applicable to one share of Common Stock.

     The adjustment shall become effective immediately after the record date for
the determination of stockholders entitled to receive such distribution (for
purposes of this Section 11.09 only, the "Record Date").

     No adjustment will be made in the event that the amount of cash so
distributed applicable to one share of Common Stock is equal to or greater than
the current market price per share of the Common Stock, in which case, in lieu
of such adjustment, adequate provision shall be made so that each Securityholder
shall have the right to receive upon conversion the amount of cash such Holder
would have received had such Holder converted each Security immediately prior to
the record date for the distribution of the cash.

                                      -51-

<PAGE>

     Notwithstanding the foregoing, on and after July 1, 2010, the conversion
price shall be adjusted pursuant to this Section 11.09 only if and to the extent
such distribution amounts per share of Common Stock plus all other distribution
amounts during the previous 12-month period exceed the interest payable per
annum on the Securities on a per share basis, based on the number of shares of
Common Stock into which the Securities are convertible immediately prior to such
distribution.

SECTION 11.10. ADJUSTMENT FOR TENDER OR EXCHANGE OFFER

     Subject to the last paragraph of this Section 11.10, in the event that a
tender or exchange offer (other than an odd-lot offer) made by the Company or
any Subsidiary for all or a portion of the Common Stock shall expire and such
tender or exchange offer (including any amendment in effect immediately prior to
the expiration thereof) shall require the payment to stockholders of
consideration per share of Common Stock having a fair market value (as
determined in good faith by the Board of Directors and set forth in a certified
resolution filed with the Trustee) that, as of the last time (the "Expiration
Time") tenders or exchanges may be made pursuant to such tender or exchange
offer, exceeds 110% of the current market price per share of Common Stock at the
Expiration Time, the conversion price shall be reduced in accordance with the
following formula:

                       AC = CC x      O x M
                                 ---------------
                                   P + (T x M)
               where:

                      AC  =  the adjusted conversion price.

                      CC  =  the conversion price in effect immediately prior to
                             the close of business on the date of the Expiration
                             Time.

                      O   =  the number of shares of Common Stock outstanding
                             (including any tendered or exchanged shares) at the
                             Expiration Time.

                      P   =  the fair market value of the aggregate
                             consideration payable to holders of Common Stock
                             based on the acceptance (up to any maximum
                             specified in the terms of the tender or exchange
                             offer) of all shares of Common Stock validly
                             tendered or exchanged and not withdrawn as of the
                             Expiration Time (the shares of Common Stock so
                             accepted, up to any such maximum, being referred to
                             as the "Purchased Shares").

                      T   =  the number of shares of Common Stock outstanding
                             (less

                                      -52-

<PAGE>

                             any Purchased Shares) on the Expiration Time.

                      M   =  the current market price per share of Common Stock
                             at the Expiration Time.

     The adjustment shall become effective immediately prior to the opening of
business on the day following the Expiration Time.

     In the event that the Company or any Subsidiary, if applicable, 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.

SECTION 11.11. CURRENT MARKET PRICE

     For purposes of Sections 11.07, 11.08, 11.09 and 11.10, the current market
price per share of Common Stock on any date is the volume weighted average of
the Quoted Prices of the Common Stock for five consecutive Trading Days selected
by the Company commencing not more than 10 Trading Days before, and ending not
later than, the earlier of the date in question and the Trading Day before the
"ex" date, if any, with respect to the issuance or distribution requiring such
computation. The term "ex" date, when used with respect to any issuance or
distribution, means the first Trading Day on which the Common Stock trades
regular way in the market from which the Quoted Price is then to be determined
without the right to receive such issuance or distribution.

SECTION 11.12. WHEN ADJUSTMENT MAY BE DEFERRED

     No adjustment in the conversion price need be made unless the adjustment
would require an increase or decrease of at least 1% in the conversion price
then in effect. Any adjustments which are not made shall be earned forward and
taken into account in any subsequent adjustment. All calculations under this
Article shall be made to the nearest cent or to the nearest 1/100th of a share,
as the case may be, with 0.005 cents and 500/1,000 of a share to be rounded up.

SECTION 11.13. WHEN NO ADJUSTMENT REQUIRED

     No adjustment need be made for rights to purchase Common Stock pursuant to
a Company plan for reinvestment of dividends or interest.

     No adjustment need be made for a change in the par value (including a
change to no par value) of the Common Stock.

     To the extent the Securities become convertible into cash, no adjustment
need be made thereafter as to the cash. Interest will not accrue on the cash.

                                      -53-

<PAGE>

     Notwithstanding any provision to the contrary in this Indenture, no
adjustment shall be made in the conversion price, which would have the effect of
reducing the conversion price below the par value of the Common Stock.

     Notwithstanding any provision to the contrary in this Indenture, rights
distributed by the Company to its stockholders pursuant to the Company's Rights
Agreement dated as of August 9, 2002 between the Company and Mellon Investor
Services, LLC as Rights Agent, as it may be amended from time to time, and any
successor or similar stockholders rights plan, which rights are not exercisable
until the occurrence of a specified event or events (a "Triggering Event") shall
be deemed not have been distributed for purposes of this Article 11 (and no
adjustment to the conversion price shall be required) until the occurrence of
such Triggering Event.

SECTION 11.14. NOTICE OF ADJUSTMENT

     Whenever the conversion price is adjusted, the Company shall promptly mail
to Securityholders a notice of the adjustment and file with the Trustee a
certificate from the Company's independent public accountants briefly stating
the facts requiring the adjustment and the manner of computing it. In the
absence of manifest error, such certificate shall be presumptive evidence that
the adjustment is correct.

SECTION 11.15. VOLUNTARY REDUCTION

     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 20 days and if the reduction is
irrevocable during the period; provided, however, that no such reduction shall
be taken into account for purposes of determining whether the last sale price of
the Common Stock equals or exceeds 105% of the conversion price in connection
with an event that would otherwise be a Fundamental Change pursuant to Section
4.05. Notwithstanding any provision to the contrary in this Indenture, the
reduction of the conversion price pursuant to this Section 11.15 shall not
require the consent of the Trustee or any Securityholder.

     Whenever the conversion price is reduced, the Company shall mail to
Securityholders and the Trustee a notice of the reduction. The Company shall
mail the notice at least 15 days before the date the reduced conversion price
takes effect. The notice shall state the reduced conversion price and the period
during which it will be in effect.

     A reduction of the conversion price is deemed not to be in effect for
purposes of calculating adjustments pursuant to Sections 11.06 through 11.10.

     Subject to the first paragraph of this Section 11.15, the Company may
reduce the conversion price, for the remaining term of the Securities or any
shorter term, in addition to those adjustments required by Sections 11.06,
11.07, 11.08, 11.09 and 11.10, as it considers to be advisable in order to avoid
or diminish any income tax to any holders of shares of Common Stock resulting
from any dividend or distribution of stock or issuance of rights or

                                      -54-

<PAGE>

warrants to purchase or subscribe for stock or from any event treated as such
for income tax purposes.

SECTION 11.16. NOTICE OF CERTAIN TRANSACTIONS

     If:

     (1)  the Company takes any action which would require an adjustment in the
conversion price pursuant to Section 11.08 but, in lieu of such adjustment, the
Securityholders are entitled to participate therein (as described in the last
paragraph of Section 11.08);

     (2)  the Company takes any action that would require a supplemental
indenture pursuant to Section 11.17; or

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

the Company shall mail to Securityholders and the Trustee a notice stating the
record date for any such distribution or the effective date of any such
subdivision, combination, reclassification, consolidation, merger, transfer,
lease, liquidation or dissolution. The Company shall mail the notice at least 15
days before such record date. Failure to mail the notice or any defect in it
shall not affect the validity of any transaction referred to in clause (1), (2)
or (3) of this Section.

SECTION 11.17. PROVISIONS IN CASE OF CONSOLIDATION, MERGER OF THE COMPANY OR
     TRANSFER OR LEASE

     If the Company is a party to a consolidation or merger or a transfer or
lease of all or substantially all of its assets not prohibited by Section 6.01
or a merger which reclassifies or changes its outstanding Common Stock, the
Person formed by such consolidation or resulting from such merger or which
assumes or leases such assets shall enter into a supplemental indenture.

     The supplemental indenture shall provide that the Holder of a Security may
convert it into the kind and amount of securities, cash or other assets
receivable upon the consolidation, merger, transfer or lease by a Holder (other
than any party to such transaction or any of its affiliates) of the number of
shares of Common Stock into which such Security might have been converted
immediately before the effective date of such transaction, assuming such holder
of Common Stock failed to exercise his rights of election, if any, as to the
kind or amount of securities, cash or other property receivable upon such
consolidation, merger, transfer or lease (provided that, if the kind or amount
of securities, cash or other property receivable upon such consolidation,
merger, transfer or lease is not the same for each share of Common Stock held
immediately prior to such consolidation, merger, transfer or lease by others
than the parties to such transaction or their affiliates and in respect of which
such rights of election shall not have been exercised ("non-electing share"),
then for the purposes

                                      -55-

<PAGE>

of this Section the kind and amount of securities, cash and other property
receivable upon such consolidation, merger, transfer or lease by each
non-electing share shall be deemed to be the kind and amount so receivable per
share by a plurality of the non-electing shares). The supplemental indenture
shall provide for adjustments, which shall be as nearly equivalent as may be
practical to the adjustments provided for in this Article. If the issuer of
securities deliverable upon conversion of Securities is an affiliate of the
surviving, transferee or lessee corporation, that issuer shall join in the
supplemental indenture. The successor Company shall mail to each Securityholder
a notice briefly describing the supplemental indenture.

     If this Section applies to a particular event, Section 11.06 shall not
apply to such event.

SECTION 11.18. COMPANY DETERMINATION FINAL

     Subject to compliance with the terms of this Indenture (including, without
limitation, Section 11.14) and of the Securities, any determination which the
Company or its Board of Directors must make pursuant to Section 11.03, 11.06,
11.08, 11.10, 11.11 or 11.12 shall be conclusive.

SECTION 11.19. TRUSTEE'S DISCLAIMER

     The Trustee has no duty to determine when an adjustment under this Article
should be made, how it should be made or what it should be. The Trustee has no
duty to determine the market price or market value of any fractional or other
share. The Trustee has no duty to determine whether any provisions of a
supplemental indenture under Section 11.17 are correct. The Trustee makes no
representation as to the validity or value of any securities or assets issued
upon conversion of the 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 as the Trustee.

                                   ARTICLE 12.

                                  SUBORDINATION

SECTION 12.01. AGREEMENT TO SUBORDINATE

     The Company agrees, and each Securityholder by accepting a Security agrees,
that the indebtedness evidenced by the Securities is subordinated in right of
payment, to the extent and in the manner provided in this Article, to the prior
payment in full of all Senior Indebtedness, and that the subordination is for
the benefit of the holders of Senior Indebtedness.

SECTION 12.02. CERTAIN DEFINITIONS

     "Senior Indebtedness" means:

                                      -56-

<PAGE>

     (a)  the principal of, interest (including, to the extent permitted by
applicable law, interest on or after the commencement of a proceeding referred
to in clauses (5) or (6) of Section 7.01 whether or not representing an allowed
claim in such proceeding) on and any other amounts owing with respect to (i) any
indebtedness of the Company and any Subsidiary, now or hereafter outstanding, in
respect of borrowed money (other than the Securities), (ii) any indebtedness of
the Company and any Subsidiary, now or hereafter outstanding, evidenced by a
bond, note, debenture, capitalized lease, reimbursement obligation with respect
to any letter of credit or other similar instrument, (iii) any other written
obligation of the Company and any Subsidiary, now or hereafter outstanding, to
pay money issued or assumed as all or part of the consideration for the
acquisition of property, assets or securities and (iv) any guaranty or
endorsement (other than for collection or deposit in the ordinary course of
business) or discount with recourse of, or other agreement (contingent or
otherwise) to purchase, repurchase or otherwise acquire, to supply or advance
funds or to become liable with respect to (directly or indirectly), any
indebtedness or obligation of any person of the type referred to in the
preceding subclauses (i), (ii) and (iii) now or hereafter outstanding; and

     (b)  any refundings, renewals or extensions of any indebtedness or other
obligation described in clause (a) of this Section 12.02.

     Notwithstanding the foregoing, if, by the terms of the instrument creating
or evidencing any indebtedness or obligation referred to in clauses (a) and (b)
above, it is expressly provided that such indebtedness or obligation is not
senior in right of payment to the Securities, such indebtedness or obligation
shall not be included as Senior Indebtedness.

     "Representative" means the indenture trustee or other trustee, agent or
representative for an issue of Senior Indebtedness.

SECTION 12.03. LIQUIDATION; DISSOLUTION; BANKRUPTCY

     Upon any distribution to creditors of the Company in a liquidation,
dissolution or winding up of the Company or in a bankruptcy, reorganization,
insolvency, receivership or similar proceeding relating to the Company or its
property:

     (1)  holders of Senior Indebtedness shall be entitled to receive payment in
full, in cash or in a manner satisfactory to the holders of such Senior
Indebtedness, of all Senior Indebtedness before Securityholders shall be
entitled to receive any payments of principal of or premium, if any, or interest
on Securities; and

     (2)  until the Senior Indebtedness is paid in full in cash or in a manner
satisfactory to the holders of such Senior Indebtedness, any distribution to
which Securityholders would be entitled but for this Article shall be made to
holders of Senior Indebtedness as their interests may appear, except that
Securityholders may receive securities that are subordinated to Senior
Indebtedness to at least the same extent as the Securities.

                                      -57-

<PAGE>

     A distribution may consist of cash, securities or other property.

SECTION 12.04. COMPANY NOT TO MAKE PAYMENTS WITH RESPECT TO SECURITIES IN
     CERTAIN CIRCUMSTANCES

     (a)  Upon the maturity of any Senior Indebtedness by lapse of time,
acceleration or otherwise, all principal thereof, premium, if any, and interest
thereon and any other amounts owing in respect thereof shall first be paid in
full, or such payment duly provided for in cash or in a manner satisfactory to
the holders of such Senior Indebtedness, before any payment is made on account
of the principal of or premium, if any, or interest on the Securities or to
acquire any of the Securities.

     (b)  Upon the happening of a default or event of default in the payment of
the principal, premium, if any, or interest on the Senior Indebtedness, then,
unless such default or event of default has been cured or waived or shall have
ceased to exist, no payment shall be made by the Company with respect to the
principal, premium, if any, or interest on (or otherwise in respect of) the
Securities or to acquire any of the Securities.

     (c)  Upon the happening of a default or event of default in respect of the
Senior Indebtedness (other than a default or event of default in payment of the
principal, premium, if any, or interest on the Senior Indebtedness) and if the
Trustee and the Company receives a notice of such default or event of default
from the holders of the Senior Indebtedness or their Representative (a "Payment
Blockage Notice"), then no payment shall be made by the Company with respect to
the principal, premium, if any, or interest on (or otherwise in respect of) the
Securities until the earlier of (i) the date on which such default or event of
default shall have been cured or waived or shall have ceased to exist or (ii)
the 179th day after the date of such receipt of such Payment Blockage Notice. No
more than one Payment Blockage Notice shall be effective for purposes of this
section during any 365 consecutive day period. For purposes of this paragraph,
no such default or event of default that existed upon first delivery of any
Payment Blockage Notice shall be, or be made, the basis for a subsequent Payment
Blockage Notice unless such default or event of default shall have been cured or
waived for a period of 180 consecutive days.

SECTION 12.05. ACCELERATION OF SECURITIES

     If payment of the Securities is accelerated because of an Event of Default,
the Company shall promptly notify holders of Senior Indebtedness of the
acceleration.

SECTION 12.06. WHEN DISTRIBUTION MUST BE PAID OVER

     If a distribution is made to Securityholders that, because of this Article,
should not have been made to them, the Securityholders who receive the
distribution shall hold it in trust for holders of Senior Indebtedness and pay
it over to them as their interests may appear.

                                      -58-

<PAGE>

SECTION 12.07. NOTICE BY COMPANY

     The Company shall promptly notify the Trustee and the Paying Agent of any
facts known to the Company that would cause a payment of principal of or
premium, if any, or interest on the Securities to violate this Article.

SECTION 12.08. SUBROGATION

     After all Senior Indebtedness is paid in full and until the Securities are
paid in full, Securityholders shall be subrogated to the rights of holders of
Senior Indebtedness to receive distributions applicable to Senior Indebtedness
to the extent that distributions otherwise payable to the Securityholders have
been applied to the payment of Senior Indebtedness. A distribution made under
this Article to holders of Senior Indebtedness which otherwise would have been
made to Securityholders is not, as between the Company and Securityholders, a
payment by the Company on Senior Indebtedness.

SECTION 12.09. RELATIVE RIGHTS

     This Article defines the relative rights of Securityholders and holders of
Senior Indebtedness. Nothing in this Indenture shall:

     (1)  impair, as between the Company and Securityholders, the obligation of
the Company, which is absolute and unconditional, to pay principal of and
premium, if any, and interest on the Securities in accordance with their terms;

     (2)  affect the relative rights of Securityholders and creditors of the
Company, other than holders of Senior Indebtedness; or

     (3)  prevent the Trustee or any Securityholder from exercising its
available remedies upon a Default, subject to the rights of holders of Senior
Indebtedness to receive distributions otherwise payable to Securityholders.

     If the Company fails because of this Article to pay principal of or
premium, if any, or interest on a Security on the due date, such failure shall
nevertheless be deemed a Default.

SECTION 12.10. SUBORDINATION MAY NOT BE IMPAIRED BY COMPANY

     No right of any holder of Senior Indebtedness to enforce the subordination
of the indebtedness evidenced by the Securities shall be impaired by any act or
failure to act by the Company or by its failure to comply with the terms of this
Indenture.

SECTION 12.11. DISTRIBUTION OR NOTICE TO REPRESENTATIVE

     Whenever a distribution is to be made or a notice given to holders of
Senior Indebtedness, the distribution may be made and the notice given to their
Representative.

                                      -59-

<PAGE>

SECTION 12.12. RIGHTS OF TRUSTEE AND PAYING AGENT

     Notwithstanding any provisions of this Indenture to the contrary, the
Trustee and any Paying Agent may continue to make payments on the Securities and
shall not at any time be charged with knowledge of the existence of any facts
which would prohibit the making of such payments until it receives written
notice (received by a Trust Officer, in the case of the Trustee) reasonably
satisfactory to it that payments may not be made under this Article and, prior
to the receipt of any such notice, the Trustee, subject to the provisions of
Section 8.01, and any Agent shall be entitled to assume conclusively that no
such facts exist. The Company, an Agent, a Representative or a holder of Senior
Indebtedness may give the notice. If an issue of Senior Indebtedness has a
Representative, only the Representative (or any Representative, if more than
one) may give the notice with respect to such Senior Indebtedness.

     The Trustee shall be entitled to rely on the delivery to it of a written
notice by a Person representing himself to be a holder of Senior Indebtedness
(or a Representative) to establish that such notice has been given by a holder
of Senior Indebtedness (or a Representative), and shall be entitled to rely on
any written notice by a Person representing himself to be a holder of Senior
Indebtedness to the effect that such issue of Senior Indebtedness has no
Representative.

     Except as provided in Section 9.02, any deposit of monies by the Company
with the Trustee or any Paying Agent (whether or not in trust) for the payment
of the principal of or premium, if any, or interest on, or Purchase Price or
Fundamental Change Purchase Price, if any, of any Securities shall be subject to
the provisions of this Article 12, except that if, at least three Business Days
prior to the date on which by the terms of this Indenture any such monies may
become payable for any purpose (including, without limitation, the payment of,
principal of, or premium, if any, or interest on any Security), the Trustee
shall not have received with respect to such monies the notice provided for in
this Section 12.12, then the Trustee shall have full power and authority to
receive such monies and to 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 within three Business Days prior to or on or after such date.
This Section shall be construed solely for the benefit of the Trustee and Paying
Agent and shall not otherwise affect the rights of holders of Senior
Indebtedness. In the event that the Trustee determines in good faith that
further evidence is required with respect to the right of any Person as a holder
of Senior Indebtedness to participate in any payment or distribution pursuant to
this Article 12, the Trustee may request such Person to furnish evidence to the
reasonable satisfaction of the Trustee as to the amount of the Senior
Indebtedness held by such Person, the extent to which such Person is entitled to
participate in such payment or distribution and any other facts pertinent to the
rights of such Person under this Article 12, and, if such evidence is not
furnished, the Trustee may defer any payment to such Person pending judicial
determination as to the right of such Person to receive payment.

                                      -60-

<PAGE>

     The Trustee shall not be deemed to owe any fiduciary duty to holders of
Senior Indebtedness by virtue of the provisions of this Article 12. The
Trustee's responsibilities to the holders of Senior Indebtedness are limited to
those set forth in this Article and no implied covenants or obligations shall be
read into this Indenture. The Trustee shall not become liable to the holders of
Senior Indebtedness if it makes a payment prohibited by this Article in good
faith.

     The Trustee in its individual or any other capacity may hold Senior
Indebtedness with the same rights it would have if it were not Trustee. Any
Agent may do the same with like rights.

SECTION 12.13. EFFECTUATION OF SUBORDINATION BY TRUSTEE

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

                                   ARTICLE 13.

                                  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 to the Company or the Trustee by the other
shall be duly given if in writing and delivered in person or by overnight
courier or mailed by first class mail or transmitted by telephone facsimile
transmission (and receipt confirmed) addressed as follows:

     If to the Company:    ICOS Corporation
                           22021 - 20/th/ Avenue N.E.
                           Bothell, Washington  98021
                           Attention: General Counsel
                           Facsimile: (425) 398-8950

                                      -61-

<PAGE>

     With a copy to:       Orrick, Herrington & Sutcliffe LLP
                           719 Second Avenue, Suite 900
                           Seattle, Washington 98104
                           Attention: Stephen M. Graham
                           Facsimile: (206) 839-4301

     If to the Trustee:    Wells Fargo Bank, National Association
                           707 Wilshire Blvd., 17/th/ Floor
                           Los Angeles, California  90017
                           Attention: Corporate Trust Department
                           Facsimile: (213) 614-3355

     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 Securityholder shall be mailed by
first-class mail to his address as shown on the register kept by the Registrar.
Failure to mail a notice or communication to a Securityholder or any defect in
it shall not affect its sufficiency with respect to other Securityholders. If
the Company mails a notice or communication to Securityholders, it shall mail a
copy to the Trustee and each Agent at the same time.

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

SECTION 13.03. COMMUNICATIONS BY HOLDERS WITH OTHER HOLDERS

     Securityholders may communicate pursuant to TIA Section 312(b) with other
Securityholders with respect to their rights under this Indenture or the
Securities. The Company, the Trustee, the Registrar and any other person shall
have the protection of TIA Section 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.

                                      -62-

<PAGE>

SECTION 13.05. STATEMENTS REQUIRED IN CERTIFICATE OR OPINION

     Each certificate or opinion with respect to compliance with a condition or
covenant provided for in this Indenture (other than pursuant to Section 5.03)
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, such examination or
investigation as is necessary to enable him to express an informed opinion as to
whether or not such covenant or condition has been complied with; and

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

SECTION 13.06. RULES BY TRUSTEE AND AGENTS

     The Trustee may make reasonable rules for action by or a meeting of
Securityholders. The Registrar, Paying Agent, New York Presenting Agent and
Conversion Agent may each make reasonable rules and set reasonable requirements
for its respective functions.

SECTION 13.07. LEGAL HOLIDAYS

     A "Legal Holiday" is a Saturday, Sunday or a day on which banking
institutions in either New York, New York or in Los Angeles, California are not
required to be open. If a payment date is a Legal Holiday at a place of payment,
payment may be made at such place on the next succeeding day that is not a Legal
Holiday, and no interest shall accrue for the intervening period. If a regular
record date is a Legal Holiday, the record date shall not be affected.

SECTION 13.08. GOVERNING LAW

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

SECTION 13.09. NO RECOURSE AGAINST OTHERS

     A director, officer, employee or stockholder, as such, of the Company shall
not have any liability for any obligations of the Company under the Securities
or this Indenture or for any claim based on, in respect of or by reason of such
obligations or their creation. Each Securityholder 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.

                                      -63-

<PAGE>

SECTION 13.10. 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.

SECTION 13.11. COUNTERPART 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 13.12. SEVERABILITY

     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.


                [Remainder of the page intentionally left blank]

                                      -64-

<PAGE>

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


                                      ICOS CORPORATION


                                      By: /s/ John Kliewer
                                          --------------------------------------
                                      Name:   John Kliewer
                                              ----------------------------------
                                      Title:  Vice President and General Counsel
                                              ----------------------------------


                                      WELLS FARGO BANK,
                                      NATIONAL ASSOCIATION


                                      By: /s/ Jeanie Mar
                                          --------------------------------------
                                      Name:   Jeanie Mar
                                              ----------------------------------
                                      Title:
                                              ----------------------------------


<PAGE>

                                    EXHIBIT A

                                FORM OF SECURITY

     [UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF
THE DEPOSITORY TRUST COMPANY 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 THE DEPOSITORY TRUST COMPANY (AND ANY PAYMENT HEREON IS MADE
TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY), ANY TRANSFER, PLEDGE OR OTHER
USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL SINCE THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN. THIS SECURITY IS A
GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND
IS REGISTERED IN THE NAME OF A DEPOSITARY OR A NOMINEE THEREOF. THIS SECURITY IS
EXCHANGEABLE FOR SECURITIES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE
DEPOSITARY OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE
INDENTURE AND, UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR
SECURITIES IN DEFINITIVE FORM, THIS SECURITY MAY NOT BE TRANSFERRED EXCEPT AS A
WHOLE BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE
DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE
DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH
SUCCESSOR DEPOSITARY.](1)

     [THIS SECURITY (OR ITS PREDECESSOR) WAS ORIGINALLY ISSUED IN A TRANSACTION
EXEMPT FROM REGISTRATION UNDER THE UNITED STATES SECURITIES ACT OF 1933, AS
AMENDED (THE "SECURITIES ACT"), AND THIS SECURITY AND THE COMMON STOCK (AND ANY
OTHER SECURITIES) ISSUABLE UPON CONVERSION THEREOF 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.](2)


----------
(1)  These paragraphs should be included only if the Security is a Global
     Security.

                                       A-1

<PAGE>

     [THE HOLDER OF THIS SECURITY AGREES FOR THE BENEFIT OF THE COMPANY THAT (A)
THIS SECURITY AND THE COMMON STOCK (AND ANY OTHER SECURITIES) ISSUABLE UPON
CONVERSION THEREOF 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) TO A NON U.S.
PERSON IN AN OFFSHORE TRANSACTION IN ACCORDANCE WITH RULE 903 OR 904 UNDER THE
SECURITIES ACT, (III) PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE
SECURITIES ACT PROVIDED BY RULE 144 THEREUNDER (IF AVAILABLE) OR (IV) PURSUANT
TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT, IN EACH OF
CASES (I) THROUGH (IV) 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. IN ANY CASE, THE HOLDER HEREOF WILL NOT
DIRECTLY OR INDIRECTLY, ENGAGE IN ANY HEDGING TRANSACTIONS WITH REGARD TO THE
SECURITIES EXCEPT AS PERMITTED UNDER THE SECURITIES ACT.](2)

     [THE HOLDER OF THIS SECURITY IS ENTITLED TO THE BENEFITS OF A REGISTRATION
RIGHTS AGREEMENT TO WHICH THE COMPANY IS A PARTY DATED AS OF JUNE 20, 2003
RELATING TO THE SECURITY AND, BY ITS ACCEPTANCE HEREOF, AGREES TO BE BOUND BY
AND TO COMPLY WITH THE PROVISIONS OF SUCH REGISTRATION RIGHTS AGREEMENT.](2)



----------
(2)  These paragraphs to be included only if the Security is a Transfer
     Restricted Security.

                                       A-2

<PAGE>

No.                                                                 $250,000,000
CUSIP No.


                                ICOS CORPORATION

               2% Convertible Subordinated Notes Due July 1, 2023

     ICOS Corporation, a Delaware corporation, for value received, promises to
pay to Cede & Co., or registered assigns, the principal sum of Two Hundred and
Fifty Million Dollars (U.S. $250,000,000) [or such greater or lesser amount as
is indicated on the Schedule of Exchanges of Securities on the reverse of this
Security] on July 1, 2023.(3)

          Interest Payment Dates:       January 1 and July 1,
                                        commencing January 1, 2004

          Record Dates:                 December 15 and June 15



----------
(3)  This phrase should be included only if the Security is a Global Security.

                                       A-3

<PAGE>

     Reference is hereby made to the further provisions of this Security set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

                                        ICOS CORPORATION


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


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

Authenticated:

WELLS FARGO BANK, NATIONAL
ASSOCIATION, as Trustee


By:
   -----------------------------------
   Authorized Signer



                                       A-4

<PAGE>

                              (Reverse of Security)
                                ICOS CORPORATION

               2% Convertible Subordinated Notes Due July 1, 2023


1.   INTEREST

     ICOS CORPORATION (the "Company"), a Delaware corporation, promises to pay
interest on the principal amount of this Security at the rate of 2% per annum.
The Company will pay interest semi-annually on January 1 and July 1 of each
year, commencing on January 1, 2004 to holders of Securities at the close of
business on the relevant record dates specified above. Interest on the
Securities will accrue from the most recent date to which interest has been paid
or, if no interest has been paid, from June 20,2003. Interest will be computed
on the basis of a 360-day year of twelve 30-day months.

2.   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 December 15 or June 15 next preceding the interest payment date
(including Securities that are cancelled after the record date and on or before
the interest payment date). Holders must surrender Securities to a Paying Agent
to collect principal and any premium payments. The Company will pay principal,
premium, if any, and interest in money of the United States that at the time of
payment is legal tender for payment of public and private debts.

3.   PAYING AGENT, REGISTRAR, CONVERSION AGENT

     Initially, Wells Fargo Bank, National Association (the "Trustee") will act
as Paying Agent, Registrar and Conversion Agent. The Company may change any
Paying Agent, Registrar, Conversion Agent or Co-Registrar by giving notice to
the Trustee. The Company may act as Paying Agent, Registrar, Conversion Agent or
Co-Registrar.

4.   INDENTURE

     The Company issued this Security as one of a duly authorized issue of Notes
of the Company designated as its 2% Convertible Subordinated Notes Due July 1,
2023 (the "Securities") under an Indenture dated as of June 20, 2003 (the
"Indenture"), between the Company and the Trustee. The terms of the Securities
include those stated in the Indenture. The Securities are subject to all such
terms, and Securityholders are referred to the Indenture for a statement of such
terms. Terms used herein that are defined in the Indenture shall have the
respective meanings assigned thereto in the Indenture. The Securities are
general unsecured obligations of the Company limited to

                                       A-5

<PAGE>

$250,000,000 in aggregate principal amount ($300,000,000 if the Initial
Purchasers Option is exercised in full).

5.   OPTIONAL REDEMPTION

     The Securities may not be redeemed prior to July 5, 2010, and are
redeemable, subject to the subordination provisions described below, on such
date and thereafter at the option of the Company, as a whole at any time, or in
part from time to time, at 100% of the principal amount plus accrued and unpaid
interest up to, but not including, the redemption date. If the redemption date
is on or after an interest record date but on or prior to the related interest
payment date, interest will be payable to the Holders in whose names the
Securities are registered at the close of business on the relevant record date.

6.   PURCHASE AT OPTION OF HOLDER

     Subject to the terms and conditions of the Indenture, the Company shall
become obligated to purchase, at the option of the Holder, all or any portion of
the Securities held by such Holder, in any integral multiple of $1,000, on July
1, 2010, July 1, 2013 and July 1, 2018 (each, a "Purchase Date") at a purchase
price per Security equal to 100% of the aggregate principal amount of the
Security (the "Purchase Price"), together with accrued and unpaid interest up to
but not including the Purchase Date (provided that, if the Purchase Date is on
or after an interest record date but on or prior to the related interest payment
date, interest will be payable to the Holders in whose names the Securities are
registered at the close of business on the relevant record date) upon delivery
of a Purchase Notice containing the information set forth in the Indenture, at
any time from the opening of business on the date that is 20 Business Days prior
to such Purchase Date until the close of business on the fifth Business Day
prior to such Purchase Date, and upon delivery of the Securities to the Paying
Agent by the Holder as set forth in the Indenture.

     Holders have the right to withdraw any Purchase Notice by delivering to the
Paying Agent a written notice of withdrawal in accordance with the provisions of
the Indenture.

     If cash sufficient to pay the Purchase Price of and accrued and unpaid
interest on, all Securities or portions thereof to be purchased as of the
Purchase Date is deposited with the Paying Agent on or before the Business Day
following the Purchase Date, the holder thereof shall have no other rights other
than the right to receive the Purchase Price, together with accrued and unpaid
interest up to but not including the Purchase Date, upon surrender of such
Security.

     If a Fundamental Change (as defined below) occurs, each holder of
Securities shall have the right, at the holder's option, to require the Company
to repurchase all of such holder's Securities, or any portion thereof that is an
integral multiple of $1,000, on the date (the "Fundamental Change Purchase
Date") selected by the Company that is not less than 10 nor more than 30 days
after the Final Surrender Date (as defined below), at a price equal to

                                       A-6

<PAGE>

100% of the principal amount thereof, plus accrued interest to the Fundamental
Change Purchase Date (the "Fundamental Change Purchase Price").

     Unless the Company shall have theretofore called for redemption all the
outstanding Securities, on or before the 30th day after the occurrence of a
Fundamental Change, the Company is obligated to mail or cause the Trustee to
mail to all holders of record of the Securities a notice (the "Company Notice")
describing, among other things, the occurrence of such Fundamental Change and of
the repurchase right arising as a result thereof. The Company must deliver a
copy of the Company Notice to the Trustee and cause a copy of such notice to be
published in a newspaper of general circulation in the Borough of Manhattan, The
City of New York. To exercise the repurchase right, a holder of Securities must
surrender, on or before the date which, subject to any contrary requirements of
applicable law, is 60 days after the date of mailing of the Company Notice (the
"Final Surrender Date") the Securities with respect to which the right is being
exercised, which, in the case of definitive Securities, must be duly endorsed
for transfer to the Company.

     The term "Fundamental Change" shall mean any of the following:

     (i)   a "person" or "group" (within the meaning of Sections 13(d) and
14(d)(2) of the Securities Exchange Act of 1934, as amended) becoming the
"beneficial owner" (as defined in Rule 13d-3 under such Act) of Voting Shares
(as defined below) of the Company entitled to exercise more than 50% of the
total voting power of all outstanding Voting Shares of the Company (including
any right to acquire Voting Shares that are not then outstanding of which such
person or group is deemed the beneficial owner); or

     (ii)  a change in the Board of Directors in which the individuals who
constituted the Board of Directors at the beginning of the two-year period
immediately preceding such change (together with any other director whose
election by the Board of Directors or whose nomination for election by the
stockholders of the Company was approved by a vote of at least two-thirds of the
directors then in office who either were directors at the beginning of such
period or whose election or nomination for election was previously so approved)
cease for any reason to constitute a majority of the directors then in office;
or

     (iii) any consolidation of the Company with, or merger of the Company into,
any other Person, any merger of another Person into the Company, or any sale or
transfer of all or substantially all of the assets of the Company to another
Person (other than (a) a stock-for-stock merger, (b) a merger that does not
result in any reclassification, conversion, exchange or cancellation of
outstanding shares of Common Stock, (c) a merger that is effected solely to
change the jurisdiction of incorporation of the Company or (d) any consolidation
with or merger of the Company into a wholly owned Subsidiary, or any sale or
transfer by the Company of all or substantially all of its assets to one or more
of its wholly owned Subsidiaries, in any one transaction or a series of
transactions; PROVIDED, in any such case, that the resulting corporation or each
such subsidiary assumes or guarantees the Company's obligations under the
Securities); PROVIDED, HOWEVER, that a Fundamental Change

                                       A-7

<PAGE>

shall not occur with respect to any such transaction if either (x) the last sale
price of the Common Stock for any five Trading Days during the ten Trading Days
immediately preceding the public announcement by the Company of such transaction
is at least equal to 105% of the conversion price in effect on such Trading Day
or (y) the consideration in such transaction to the holders of Common Stock
consists of cash, securities that are, or immediately upon issuance will be,
listed on a national securities exchange or quoted on The Nasdaq National
Market, or a combination of cash and such securities, and the aggregate fair
market value of such consideration (which, in the case of such securities, shall
be equal to the average of the last sale prices of such securities during the
ten consecutive Trading Days commencing with the sixth Trading Day following
consummation of the transaction) is at least 105% of the conversion price in
effect on the date immediately preceding the closing date of such transaction.

     "Voting Shares" is defined to mean all outstanding shares of any class or
series (however designated) of Capital Stock entitled to vote generally in the
election of members of the Board of Directors.

7.   NOTICE OF REDEMPTION

     Notice of redemption pursuant to paragraph 5 must be mailed at least 20
days, but not more than 60 days, before the redemption date to each holder of
Securities to be redeemed at his address as shown on the register kept by the
Registrar, and to beneficial owners as required by applicable law. Securities in
denominations larger than $1,000 may be redeemed in part, but only in integral
multiples of $1,000. On and after the redemption date, interest shall cease to
accrue on Securities or any portion of them called for redemption; PROVIDED that
funds in the requisite amount are paid or made available for payment on that
date.

8.   CONVERSION

     Subject to the terms of the Indenture, Holders may surrender Securities for
conversion into shares of Common Stock at any time on or prior to July 1, 2023
at the conversion price then in effect. The conversion right with respect to the
Security or the portion of the Security being redeemed will expire at the close
of business on the date that is two Trading Days immediately preceding such
redemption date unless the Company defaults in making payments due upon such
redemption date. The number of shares issuable upon conversion of a Security is
determined by dividing the principal amount to be converted by the conversion
price in effect on the conversion date, and rounding the result to the nearest
1/l00th of a share, with 500/1,000 of a share to be rounded up. Upon conversion,
no payment or adjustment for accrued interest on a converted Security (other
than the payment of interest to the Holder of a Security at the close of
business on a record date pursuant to paragraph 2 hereof) or for dividends or
distributions on the Common Stock will be made. The Company will deliver a check
for the current market value of such fractional shares rounded down to the
nearest cent based on the current market price of the Common Stock.

                                       A-8

<PAGE>

     A Security in respect of which a Holder has delivered a Purchase Notice
exercising the option of such Holder to require the Company to purchase such
Security may be converted only if such notice of exercise is withdrawn in
accordance with the terms of the Indenture.

     The initial conversion price is $61.50 per share of Common Stock, subject
to adjustment in certain events described in the Indenture. No adjustment in the
conversion price will be required unless such adjustment would require a change
of at least 1% in the conversion price then in effect; PROVIDED that any
adjustment that would otherwise be required to be made shall be earned forward
and taken into account in any subsequent adjustment. The Company from time to
time may voluntarily reduce the conversion price for a period of at least 20
days.

     To convert a Security, a Holder must (1) complete and sign the conversion
notice on the reverse of the Security, (2) surrender the Security to the
Conversion Agent, (3) furnish the appropriate endorsements and transfer
documents if required by the Registrar or Conversion Agent, and (4) pay any tax
or duty which may be payable in respect of any transfer involving the issue or
delivery of Common Stock in the name of a Person other than the Holder thereof.
In the case of Global Securities, conversion notices may be delivered and such
Securities may be surrendered for conversion in accordance with the Applicable
Procedures. A Holder may convert a portion of a Security if the portion is
$1,000 or an integral multiple of $1,000.

     If the Company is a party to a consolidation or merger, or a transfer or a
lease of all or substantially all of its assets or a merger which reclassifies
or changes its outstanding Common Stock, the right to convert a Security into
Common Stock may be changed into a right to convert it into securities, cash or
other assets of the Company or another person.

9.   SUBORDINATION

     The Securities are subordinated in right of payment to Senior Indebtedness,
which is defined in the Indenture. To the extent provided in the Indenture,
Senior Indebtedness must be paid before the Securities may be paid. The Company
agrees, and each Securityholder by accepting a Security agrees, to the
subordination provisions contained in the Indenture and authorizes the Trustee
to give effect to such provisions, and each Securityholder appoints the Trustee
his attorney-in-fact for any and all such purposes.

10.  DENOMINATIONS, TRANSFER, EXCHANGE

     The Securities are in registered form without coupons in denominations of
$1,000 and integral multiples of $1,000. A Holder may register the transfer of
or exchange Securities in accordance with the Indenture. The Registrar may
require a Holder, among other things, to furnish appropriate endorsements and
transfer documents and to pay any taxes or other governmental charges that may
be imposed in relation thereto by law or permitted by the Indenture.

                                       A-9

<PAGE>

11.  AMENDMENT, SUPPLEMENT, WAIVER

     Subject to certain exceptions, the Indenture or the Securities may be
amended or supplemented, with the consent of the Company and the Holders of a
majority in aggregate principal amount of the Securities at the time
outstanding, and any existing default may be waived with the consent of the
Holders of a majority in aggregate principal amount of the Securities at the
time outstanding. Without the consent of any Securityholder, the Indenture or
the Securities may be amended, INTER ALIA, to cure any ambiguity, defect or
inconsistency, to provide for assumption of Company obligations to
Securityholders in the case of a merger or acquisition, or to make any change
that does not materially adversely affect the rights of any Securityholder.

12.  DEFAULTS AND REMEDIES

     An Event of Default is default in the payment of interest on any Security
that continues for 30 days, whether or not such payment is prohibited or
restricted by the subordination provisions of the Indenture; default in payment
of principal of or premium, if any, on any Security when due and payable,
whether or not such payment is prohibited or restricted by the subordination
provisions of the Indenture; default in payment of the Purchase Price or
Fundamental Change Purchase Price to be paid upon a purchase at the option of
the Holder pursuant to paragraph 6; default in the performance of any other of
the covenants or agreements of the Company in the Indenture that continues for
60 days after written notice to it by the Trustee or holders of at least 25%
aggregate principal amount of Securities at the time outstanding; failure to
make any payment when due, including any applicable grace period in respect of
indebtedness of the Company if such payment exceeds $20,000,000 or acceleration
of payments with respect to indebtedness of the Company in excess of
$20,000,000; and certain events of bankruptcy or insolvency. If an Event of
Default occurs and is continuing, the Trustee or the holders of at least 25% in
aggregate principal amount of the Securities at the time outstanding may declare
the principal of, and accrued interest on, all the Securities to be due and
payable immediately. If the Event of Default relates to bankruptcy, insolvency,
or reorganization, the Securities shall become due and payable immediately upon
the occurrence of such Events of Default, subject to applicable law.

     Securityholders 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 aggregate principal amount of the
Securities may direct the Trustee in its exercise of any trust or power. The
Trustee may withhold from Securityholders notice of any continuing default
(except a default in payment of principal or premium, if any, or interest) if it
determines that withholding notice is in their interests. The Company must
furnish an annual compliance certificate to the Trustee.

                                      A-10

<PAGE>

13.  TRUSTEE DEALINGS WITH COMPANY

     The Trustee and any agent under the Indenture, 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 or agent.

14.  NO RECOURSE AGAINST OTHERS

     A director, officer, employee or stockholder, as such, of the Company shall
have no 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.

15.  AUTHENTICATION

     This Security shall not be valid until authenticated by the manual
signature of the Trustee or an authenticating agent on the face hereof.

16.  ABBREVIATIONS

     Customary abbreviations may be used in the name of a Securityholder or an
assignee, such as but not limited to: TEN COM (= tenants in common), TEN ENT (=
tenants by the entireties), 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).

17.  CUSIP NUMBERS

     Pursuant to a recommendation promulgated by the Committee on Uniform
Security Identification Procedures the Company has caused CUSIP numbers to be
printed on the Securities and has directed the Trustee to use CUSIP numbers in
notices of redemption as a convenience to Securityholders. No representation is
made as to the accuracy of such numbers either as printed on the Securities or
as contained in any notice of redemption.

18.  GOVERNING LAW

     The laws of the State of New York shall govern the Indenture and the
Securities without giving effect to such state's conflicts of law principles.

     THE COMPANY WILL FURNISH TO ANY SECURITYHOLDER UPON WRITTEN REQUEST AND
WITHOUT CHARGE A COPY OF THE INDENTURE. IT ALSO WILL FURNISH THE TEXT OF THIS
SECURITY IN LARGER TYPE. REQUESTS MAY BE MADE TO: ICOS CORPORATION, 22021-20/th/
AVENUE S.E., BOTHELL, WASHINGTON, 98021, ATTENTION: INVESTOR RELATIONS

                                      A-11

<PAGE>

                                CONVERSION NOTICE


To:  ICOS Corporation

     The undersigned owner of this Security hereby irrevocably exercises the
option to convert this Security, or the portion hereof (which is $1,000 or an
integral multiple thereof) below designated, into shares of ICOS Corporation
Common Stock in accordance with the terms of the Indenture referred to in this
Security, and directs that the shares issuable and deliverable upon conversion,
together with any check in payment for fractional shares and any Securities
representing any unconverted principal amount hereof, be issued and delivered to
the registered holder hereof unless a different name has been indicated below.
If shares are to be issued in the name of a Person other than the undersigned,
the undersigned will pay all transfer taxes payable with respect thereto.

     To convert this Security into ICOS Corporation Common Stock of the Company,
check the box: [_].

     To convert only part of this Security, state the amount (must be $1,000 or
any whole multiple thereof): $__________.

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

--------------------------------------------------------------------------------
      (Insert other Person's social security or tax identification number)

--------------------------------------------------------------------------------
            (Print or type other Person's name, address and zip code)

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

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


Date:                          Your signature:
     --------------------                     ----------------------------------
                                              (Sign exactly as your name appears
                                                 on the face of this Security)

                               Signature Guaranteed:
                                                    ----------------------------

                                      A-12

<PAGE>

                                 ASSIGNMENT FORM

     To assign this Security or, in the event of conversion, shares of ICOS
Corporation Common Stock, fill in the form below:

     I or we assign and transfer this Security or, _____ shares of ICOS
Corporation Common Stock, to

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

--------------------------------------------------------------------------------
        (Insert assignee's social security or tax identification number)

--------------------------------------------------------------------------------
              (Print or type assignee's name, address and zip code)

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

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

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

and irrevocably appoint __________________________________________ agent to

transfer this Security on the books of the Company. The agent may substitute

another to act for him.


Date:                          Your signature:
     --------------------                     ----------------------------------
                                              (Sign exactly as your name appears
                                                 on the face of this Security)

                               Signature Guaranteed:
                                                    ----------------------------


                                      A-13

<PAGE>

                     SCHEDULE OF EXCHANGES OF SECURITIES(4)

     The following exchanges, redemptions, repurchases or conversions of a part
of this Global Security have been made:


 Principal Amount
  of this Global                            Amount of           Amount of
     Security                              Decrease in         Increase in
 Following  Such        Authorized          Principal           Principal
  Decrease Date        Signatory of         Amount of           Amount of
   of Exchange          Securities         this Global         this Global
  (or Increase)         Custodian           Security            Security
------------------  ------------------  ------------------  ------------------




----------
(4)  This schedule should be included only if the Security is a Global Security.

                                      A-14

<PAGE>

            CERTIFICATE TO BE DELIVERED UPON EXCHANGE OR REGISTRATION
                OR TRANSFER OF TRANSFER RESTRICTED SECURITIES(5)

Re:  2% Convertible Subordinated Notes due July 1, 2023 (the "Securities")
     of ICOS Corporation.

     This certificate relates to $__________ principal amount of Securities
owned in (check applicable box)

     [_] book-entry or [_] definitive form by _______________ (the
"Transferor").

     The Transferor has requested a Registrar or the Trustee to exchange or
register the transfer of such Securities.

     In connection with such request and in respect of each such Security, the
Transferor does hereby certify that the Transferor is familiar with transfer
restrictions relating to the Securities as provided in Section 2 of the
Indenture dated as of June 20, 2003 between ICOS Corporation and Wells Fargo
Bank, National Association (the "Indenture"), and the transfer of such Security
is being made pursuant to an effective registration statement under the
Securities Act of 1933, as amended (the "Securities Act") (check applicable box)
or the transfer or exchange, as the case may be, of such Security does not
require registration under the Securities Act because (check applicable box):

     [_]  Such Security is being transferred pursuant to an effective
          registration statement under the Securities Act.

     [_]  Such Security is being acquired for the Transferor's own account,
          without transfer.

     [_]  Such Security is being transferred to the Company or a Subsidiary (as
          defined in the Indenture)

     [_]  Such Security is being transferred to a person the Transferor
          reasonably believes is a "qualified institutional buyer" (as defined
          in Rule 144A or any successor provision thereto ("Rule 144A") under
          the Securities Act) that is purchasing for its own account or for the
          account of a "qualified institutional buyer", in each case to whom
          notice has been given that the transfer is being made in reliance on
          such Rule 144A, and in each case in reliance on Rule 144A.

     [_]  Such Security is being transferred to a non-U.S. person in an offshore
          transaction in accordance with Rule 903 and Rule 904 under the
          Securities Act.

                                      A-15

<PAGE>

     [_]  Such Security is being transferred pursuant to and in compliance with
          an exemption from the registration requirements under the Securities
          Act in accordance with Rule 144 (or any successor thereto) ("Rule
          144") under the Securities Act.

     [_]  Such Security is being transferred pursuant to and in compliance with
          an exemption from the registration requirements of the Securities Act
          (other than an exemption referred to above) and as a result of which
          such Security will, upon such transfer, cease to be a "restricted
          security" within the meaning of Rule 144 under the Securities Act.

     The Transferor acknowledges and agrees that, if the transferee will hold
any such Securities in the form of beneficial interests in a global Security
which is a "restricted security" within the meaning of Rule 144 under the
Securities Act, then such transfer can only be made (a) pursuant to Rule 144A
under the Securities Act and such transferee must be a "qualified institutional
buyer" (as defined in Rule 144A) or (b) to a non-U.S. person in an offshore
transaction in accordance with Rule 903 and Rule 904 under the Securities Act.


Date:
     ---------------------------------  ----------------------------------------
                                               (Insert Name of Transferor



----------
(5)  This certificate should only be included if this Security is a Transfer
     Restricted Security.

                                      A-16