<PAGE>

                                                                     EXHIBIT 4.1

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


                           ICOS CORPORATION, Issuer

                                      to

                           _______________, Trustee

                                _______________

                                   INDENTURE

                      Dated as of ___________ ___, 200__

                                _______________

                                Debt Securities


      ==================================================================
<PAGE>

Reconciliation and tie between Indenture, dated as of ____________ ___, 200__,
and the Trust Indenture Act of 1939, as amended.


<TABLE>
<CAPTION>
Trust Indenture Act                                                        Indenture
of 1939 Section                                                            Section
---------------                                                            ---------
<S>                                                                        <C>
   310(a)(1)...........................................................    6.12
      (a)(2)...........................................................    6.12
      (a)(3)...........................................................    TIA
      (a)(4)...........................................................    Not applicable
      (a)(5)...........................................................    TIA
      (b)..............................................................    6.10; 6.12; TIA

   311(a)..............................................................    TIA
      (b)..............................................................    TIA

   312(a)..............................................................    6.8
      (b)..............................................................    TIA
      (c)..............................................................    TIA

  313(a)..............................................................     6.7; TIA
      (b)..............................................................    TIA
      (c)..............................................................    TIA
      (d)..............................................................    TIA

   314(a)..............................................................    9.6; 9.7; TIA
      (b)..............................................................    Not applicable
      (c)(1)...........................................................    1.2
      (c)(2)...........................................................    1.2
      (c)(3)...........................................................    Not applicable
      (d)..............................................................    Not applicable
      (e)..............................................................    TIA
      (f)..............................................................    TIA

   315(a)..............................................................    TIA
      (b)..............................................................    6.6
      (c)..............................................................    TIA
      (d)(1)...........................................................    TIA
      (d)(2)...........................................................    TIA
      (d)(3)...........................................................    TIA
      (e)..............................................................    TIA
   316(a)(last sentence)...............................................    1.1
      (a)(1)(A)........................................................    5.2; 5.8
      (a)(1)(B)........................................................    5.7
      (b)..............................................................    5.9; 5.10
      (c)..............................................................    TIA
</TABLE>

<PAGE>

<TABLE>
<S>                                                                        <C>
   317(a)(1)...........................................................    5.3
      (a)(2)...........................................................    5.4
      (b)..............................................................    9.3

   318(a)..............................................................    1.11
      (b)..............................................................    TIA
      (c)..............................................................    1.11; TIA
</TABLE>

__________________
     This reconciliation and tie section does not constitute part of the
Indenture.

                                      -2-
<PAGE>

                                   CONTENTS
<TABLE>
<S>                                                                                                                        <C>
ARTICLE 1  Definitions and Other Provisions of General Application.......................................................   1

     Section 1.1     Definitions.........................................................................................   1
     Section 1.2     Compliance Certificates and Opinions................................................................   7
     Section 1.3     Form of Document Delivered to Trustee...............................................................   7
     Section 1.4     Acts of Holders.....................................................................................   8
     Section 1.5     Notices, etc., to Trustee and Company...............................................................   9
     Section 1.6     Notice to Holders; Waiver...........................................................................   9
     Section 1.7     Headings and Table of Contents......................................................................  10
     Section 1.8     Successors and Assigns..............................................................................  10
     Section 1.9     Separability........................................................................................  10
     Section 1.10    Benefits of Indenture...............................................................................  10
     Section 1.11    Governing Law.......................................................................................  11
     Section 1.12    Legal Holidays......................................................................................  11

ARTICLE 2  Security Forms................................................................................................  11

     Section 2.1     Forms Generally.....................................................................................  11
     Section 2.2     Form of Face of Security............................................................................  12
     Section 2.3     Form of Reverse of Security.........................................................................  13
     Section 2.4     Form of Trustee's Certificate of Authentication.....................................................  17

ARTICLE 3  The Securities................................................................................................  17

     Section 3.1     Amount Unlimited; Issuable in Series................................................................  17
     Section 3.2     Denominations.......................................................................................  20
     Section 3.3     Execution, Authentication, Delivery and Dating......................................................  20
     Section 3.4     Temporary Securities................................................................................  22
</TABLE>

                                      -i-
<PAGE>

<TABLE>
<S>                                                                                                                            <C>
     Section 3.5     Registration, Registration of Transfer and Exchange.....................................................  22
     Section 3.6     Replacement Securities..................................................................................  24
     Section 3.7     Payment of Interest; Interest Rights Preserved..........................................................  24
     Section 3.8     Persons Deemed Owners...................................................................................  26
     Section 3.9     Cancellation............................................................................................  26
     Section 3.10    Computation of Interest.................................................................................  26
     Section 3.11    CUSIP Numbers...........................................................................................  26

ARTICLE 4  Satisfaction, Discharge and Defeasance............................................................................  27

     Section 4.1     Termination of Company's Obligations Under the Indenture................................................  27
     Section 4.2     Application of Trust Funds..............................................................................  28
     Section 4.3     Applicability of Defeasance Provisions; Company's Option to Effect Defeasance or Covenant Defeasance....  28
     Section 4.4     Defeasance and Discharge................................................................................  28
     Section 4.5     Covenant Defeasance.....................................................................................  29
     Section 4.6     Conditions to Defeasance or Covenant Defeasance.........................................................  29
     Section 4.7     Deposited Money and Government Obligations to Be Held in Trust..........................................  31
     Section 4.8     Transfers and Distribution at Company Request...........................................................  31

ARTICLE 5  Defaults and Remedies.............................................................................................  32

     Section 5.1     Events of Default.......................................................................................  32
     Section 5.2     Acceleration, Rescission and Annulment..................................................................  34
     Section 5.3     Collection of Indebtedness and Suits for Enforcement by Trustee.........................................  34
     Section 5.4     Trustee May File Proofs of Claim........................................................................  35
     Section 5.5     Trustee May Enforce Claims Without Possession of Securities.............................................  35
</TABLE>

                                     -ii-
<PAGE>

<TABLE>
<S>                                                                                                                        <C>
     Section 5.6     Delay or Omission Not Waiver........................................................................  35
     Section 5.7     Waiver of Past Defaults.............................................................................  35
     Section 5.8     Control by Majority.................................................................................  35
     Section 5.9     Limitation on Suits by Holders......................................................................  36
     Section 5.10    Rights of Holders to Receive Payment................................................................  36
     Section 5.11    Application of Money Collected......................................................................  36
     Section 5.12    Restoration of Rights and Remedies..................................................................  37
     Section 5.13    Rights and Remedies Cumulative......................................................................  37

ARTICLE 6  The Trustee...................................................................................................  37

     Section 6.1     Certain Duties and Responsibilities.................................................................  37
     Section 6.2     Rights of Trustee...................................................................................  38
     Section 6.3     Trustee May Hold Securities.........................................................................  40
     Section 6.4     Money Held in Trust.................................................................................  40
     Section 6.5     Trustee's Disclaimer................................................................................  40
     Section 6.6     Notice of Defaults..................................................................................  40
     Section 6.7     Reports by Trustee to Holders.......................................................................  40
     Section 6.8     Securityholder Lists................................................................................  41
     Section 6.9     Compensation and Indemnity..........................................................................  41
     Section 6.10    Replacement of Trustee..............................................................................  42
     Section 6.11    Acceptance of Appointment by Successor..............................................................  43
     Section 6.12    Eligibility; Disqualification.......................................................................  44
     Section 6.13    Merger, Conversion, Consolidation or Succession to Business.........................................  44
     Section 6.14    Appointment of Authenticating Agent.................................................................  45
</TABLE>

                                     -iii-
<PAGE>

<TABLE>
<S>                                                                                                                        <C>
     Section 6.15    Trustee's Application for Instructions From the Company.............................................  46

ARTICLE 7  Consolidation, Merger or Sale by the Company..................................................................  47

     Section 7.1     Consolidation, Merger or Sale of Assets Permitted...................................................  47

ARTICLE 8  Supplemental Indentures.......................................................................................  47

     Section 8.1     Supplemental Indentures Without Consent of Holders..................................................  47
     Section 8.2     With Consent of Holders.............................................................................  48
     Section 8.3     Compliance With Trust Indenture Act.................................................................  49
     Section 8.4     Execution of Supplemental Indentures................................................................  49
     Section 8.5     Effect of Supplemental Indentures...................................................................  50
     Section 8.6     Reference in Securities to Supplemental Indentures..................................................  50

ARTICLE 9  Covenants.....................................................................................................  50

     Section 9.1     Payment of Principal, Premium, if Any, and Interest.................................................  50
     Section 9.2     Maintenance of Office or Agency.....................................................................  50
     Section 9.3     Money for Securities to Be Held in Trust; Unclaimed Money...........................................  51
     Section 9.4     Corporate Existence.................................................................................  52
     Section 9.5     Insurance...........................................................................................  52
     Section 9.6     Reports by the Company..............................................................................  52
     Section 9.7     Annual Review Certificate; Notice of Default........................................................  53
     Section 9.8     Provision of Financial Statements...................................................................  53

ARTICLE 10 Redemption....................................................................................................  54

     Section 10.1    Applicability of Article............................................................................  54
     Section 10.2    Election to Redeem; Notice to Trustee...............................................................  54
     Section 10.3    Selection of Securities to Be Redeemed..............................................................  54
</TABLE>

                                     -iv-
<PAGE>

<TABLE>
<S>                                                                                                                        <C>
     Section 10.4    Notice of Redemption................................................................................  55
     Section 10.5    Deposit of Redemption Price.........................................................................  55
     Section 10.6    Securities Payable on Redemption Date...............................................................  56
     Section 10.7    Securities Redeemed in Part.........................................................................  56

ARTICLE 11 Sinking Funds.................................................................................................  56

     Section 11.1    Applicability of Article............................................................................  56
     Section 11.2    Satisfaction of Sinking Fund Payments With Securities...............................................  57
     Section 11.3    Redemption of Securities for Sinking Fund...........................................................  57
</TABLE>

                                      -v-
<PAGE>

     INDENTURE, dated as of __________ __, 200__, from ICOS CORPORATION, a
Delaware corporation (the "Company"), as issuer, to _________________, a
____________ corporation, as Trustee (the "Trustee").

                                   RECITALS

     The Company has duly authorized the execution and delivery of this
Indenture to provide for the issuance from time to time of its unsecured
debentures, notes or other evidences of indebtedness ("Securities") to be issued
in one or more series as herein provided.

     All things necessary to make the Securities, when executed by the Company,
the valid obligations of the Company, and to make this Indenture a valid
agreement of the Company, in accordance with their and its terms, have been
done.

     For and in consideration of the premises and the purchase of the Securities
by the Holders thereof, it is mutually covenanted and agreed as follows for the
equal and ratable benefit of the Holders of the Securities:

                                   ARTICLE 1

            Definitions and Other Provisions of General Application

Section 1.1  Definitions

     (a)     For all purposes of this Indenture, except as otherwise expressly
provided or unless the context otherwise requires:

             (1)    the terms defined in this Article have the meanings assigned
     to them in this Article and include the plural as well as the singular;

             (2)    all other terms used herein which are defined in the Trust
     Indenture Act, either directly or by reference therein, have the meanings
     assigned to them therein;

             (3)    all accounting terms not otherwise defined herein have the
     meanings assigned to them in accordance with generally accepted accounting
     principles; and

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

     "Affiliate" of any specified Person means any Person directly or indirectly
      ---------
controlling or controlled by, or under direct or indirect common control with
such specified Person.  For 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,
<PAGE>

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 Paying Agent or Registrar.
      -----

     Authenticating Agent" means any authenticating agent appointed by the
     --------------------
Trustee pursuant to Section 6.13.

     "Authorized Newspaper" means a newspaper of general circulation, in the
      --------------------
English language, customarily published on each Business Day whether or not
published on Saturdays, Sundays or holidays, and of general circulation in the
place in connection with which the term is used or in the financial community of
such place. Whenever successive publications in an Authorized Newspaper are
required hereunder they may be made (unless otherwise expressly provided herein)
on any Business Day and in the same or different Authorized Newspapers.

     "Board" or "Board of Directors" means the Board of Directors of the
      -----      ------------------
Company, the Executive Committee or any other duly authorized committee thereof.

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

     "Business Day," when used with respect to any Place of Payment or any other
      ------------
particular location referred to in this Indenture or in the Securities, means,
unless otherwise specified with respect to any Securities pursuant to Section
3.1, each Monday, Tuesday, Wednesday, Thursday and Friday which is not a day on
which banking institutions in that Place of Payment or particular location are
authorized or obligated by law or executive order to close.

     "Commission" means the Securities and Exchange Commission, as from time to
      ----------
time constituted, created under the Securities Exchange Act of 1934, or, if at
any time after the execution of this Indenture such Commission is not existing
and performing the duties now assigned to it under the Trust Indenture Act, then
the body performing such duties at such time.

     "Company" means the Person named as the Company in the first paragraph of
      -------
this Indenture until one or more successor corporations shall have become such
pursuant to the applicable provisions of this Indenture, and thereafter means
such successors.

     "Company Order" and "Company Request" mean, respectively, a written order
      -------------       ---------------
or request signed in the name of the Company by the Chairman of the Board, the
President or any Vice President or, with respect to Sections 3.3, 3.4, 3.5 and
6.1, any other employee of the Company named in an Officers' Certificate
delivered to the Trustee.

                                      -2-
<PAGE>

     "Corporate Trust Office" means the principal office of the Trustee at which
      ----------------------
at any particular time its corporate trust business shall be principally
administered.

     "corporation" includes corporations, associations, companies and business
      -----------
trusts.

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

     "Government Obligations" means securities which are (i) direct obligations
      ----------------------
of the United States or (ii) obligations of a Person controlled or supervised by
and acting as an agency or instrumentality of the United States the payment of
which is unconditionally guaranteed as a full faith and credit obligation by the
United States, which are not callable or redeemable at the option of the issuer
thereof, and shall also include a depositary receipt issued by a bank or trust
company as custodian with respect to any such Government Obligation or a
specific payment of interest on or principal of any such Government Obligation
held by such custodian for the account of the holder of a depositary receipt,
provided that (except as required by law) such custodian is not authorized to
--------
make any deduction from the amount payable to the holder of such depositary
receipt from any amount received by the custodian in respect of the Government
Obligation evidenced by such depositary receipt.

     "Holder" means a person in whose name a Security is registered on the
      ------
Register.

     "Indenture" means this Indenture as originally executed or as amended or
      ---------
supplemented from time to time and shall include the forms and terms (but not
defined terms established in an Officers' Certificate or a Board Resolution) of
particular series of Securities established as contemplated by Section 2.1 and
Section 3.1.

     "Indexed Security" means a Security the terms of which provide that the
      ----------------
principal amount thereof payable at Stated Maturity may be more or less than the
principal face amount thereof at original issuance.

     "Interest," when used with respect to an Original Issue Discount Security
      --------
which by its terms bears interest only after maturity, means interest payable
after maturity.

     "Interest Payment Date," when used with respect to any Security, means the
      ---------------------
Stated Maturity of an installment of interest on such Security.

     "Maturity," when used with respect to any Security, means the date on which
      --------
the principal of such Security or an installment of principal becomes due and
payable as therein or herein provided, whether at the Stated Maturity or by
declaration of acceleration, call for redemption or otherwise.

     "Officer" means the Chairman of the Board of Directors, the President, any
      -------
Executive Vice President, any Senior Vice President, any Vice President or the
Corporate Secretary of the Company.

                                      -3-
<PAGE>

     "Officers' Certificate" means a certificate signed by the Chairman of the
      ---------------------
Board, the President or any Vice President.

     "Opinion of Counsel" means a written opinion of legal counsel, who may be
      ------------------
(a) the senior attorney employed by the Company, (b) Perkins Coie LLP, or (c)
other counsel designated by the Company and who shall be reasonably acceptable
to the Trustee.

     "Original Issue Discount Security" means any Security which provides for an
      --------------------------------
amount less than the stated principal amount thereof to be due and payable upon
declaration of acceleration of the Maturity thereof pursuant to Section 5.2.

     "Outstanding," when used with respect to Securities, means, as of the date
      -----------
of determination, all Securities theretofore authenticated and delivered under
this Indenture, except:

               (i)    Securities theretofore cancelled by the Trustee or
     delivered to the Trustee for cancellation;

               (ii)   Securities, or portions thereof, for whose payment or
     redemption money in the necessary amount has been theretofore deposited
     with the Trustee or any Paying Agent (other than the Company) in trust or
     set aside and segregated in trust by the Company (if the Company shall act
     as its own Paying Agent) for the Holders of such Securities provided that,
                                                                 --------
     if such Securities are to be redeemed, notice of such redemption has been
     duly given pursuant to this Indenture or provisions therefor satisfactory
     to the Trustee have been made;

               (iii)  Securities, except to the extent provided in Sections 4.4
     and 4.5, with respect to which the Company has effected defeasance and/or
     covenant defeasance as provided in Article 4; and

               (iv)   Securities which have been paid pursuant to Section 3.6 or
     in exchange for or in lieu of which other Securities have been
     authenticated and delivered pursuant to this Indenture, other than any such
     Securities in respect of which there shall have been presented to the
     Trustee proof satisfactory to it that such Securities are held by a bona
     fide purchaser in whose hands such Securities are valid obligations of the
     Company;

provided, however, that in determining whether the Holders of the requisite
--------  -------
principal amount of the Outstanding Securities have given any request, demand,
authorization, direction, notice, consent or waiver hereunder, or whether
sufficient funds are available for redemption or for any other purpose, and for
the purpose of making the calculations required by section 313 of the Trust
Indenture Act, (x) the principal amount of any Original Issue Discount
Securities that may be counted in making such determination or calculation and
that shall be deemed to be Outstanding for such purpose shall be equal to the
amount of principal thereof that would

                                      -4-
<PAGE>

be (or shall have been declared to be) due and payable, at the time of such
determination, upon a declaration of acceleration of the maturity thereof
pursuant to Section 5.2, and (y) Securities owned by the Company or any other
obligor upon the Securities or any Affiliate of the Company or of such other
obligor shall be disregarded and deemed not to be outstanding, except that, in
determining whether the Trustee shall be protected in making such calculation or
in relying upon any such request, demand, authorization, direction, notice,
consent or waiver, only Securities which the Trustee knows to be so owned shall
be so disregarded. Securities so owned which have been pledged in good faith may
be regarded as outstanding if the pledgee establishes to the satisfaction of the
Trustee the pledgee's right so to act with respect to such Securities and that
the pledgee is not the Company or any other obligor upon the Securities or any
Affiliate of the Company or of such other obligor.

     "Paying Agent" means any Person authorized by the Company to pay the
      ------------
principal of, premium, if any, or interest on any Securities on behalf of the
Company.

     "Periodic Offering" means an offering of Securities of a series from time
      -----------------
to time the specific terms of which Securities, including, without limitation,
the rate or rates of interest or formula for determining the rate or rates of
interest thereon, if any, the Stated Maturity or Stated Maturities thereof, the
original issue date or dates thereof, the redemption provisions, if any, with
respect thereto, and any other terms specified as contemplated by Section 3.1
with respect thereto, are to be determined by the Company upon the issuance of
such Securities.

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

     "Place of Payment," when used with respect to the Securities of or within
      ----------------
any series, means the place or places where, subject to the provisions of
Section 9.2 the principal of, premium, if any, and interest on such Securities
are payable as specified as contemplated by Section 3.1.

     "Predecessor Security" of any particular Security means every previous
      --------------------
Security evidencing all or a portion of the same debt as that evidenced by such
particular Security; and, for the purposes of this definition, any Security
authenticated and delivered under Section 3.6 in exchange for or in lieu of a
mutilated, destroyed, lost or stolen Security shall be deemed to evidence the
same debt as the mutilated, destroyed, lost or stolen Security.

     "Redemption Date," when used with respect to any Security to be redeemed,
      ---------------
means the date fixed for such redemption by or pursuant to this Indenture.

     "Redemption Price," when used with respect to any Security to be redeemed,
      ----------------
in whole or in part, means the price at which it is to be redeemed pursuant to
this Indenture.

     "Regular Record Date" for the interest payable on any Interest Payment Date
      -------------------
on the Securities of or within any series means the date specified for that
purpose as contemplated by Section 3.1.

                                      -5-
<PAGE>

     "Responsible Officer," when used with respect to the Trustee, shall mean
      -------------------
the chairman or any vice chairman of the board of directors, the chairman or any
vice chairman of the executive committee of the board of directors, the chairman
of the trust committee, the president, any senior vice president, any vice
president, any assistant vice president, the secretary, the treasurer, any
assistant treasurer, the cashier, any assistant cashier, any senior trust
officer, any trust officer, the controller, any assistant controller, or any
other officer of the Trustee customarily performing functions similar to those
performed by the persons who at the time shall be such officers, respectively,
and also means, with respect to a particular corporate trust matter, any other
officer to whom such corporate trust matter is referred because of his knowledge
of and familiarity with the particular subject.

     "Security" or "Securities" has the meaning stated in the first recital of
      --------      ----------
this Indenture and more particularly means any Security or Securities of the
Company issued, authenticated and delivered under this Indenture.

     "Special Record Date" for the payment of any Defaulted Interest on the
      -------------------
Securities of any issue means a date fixed by the Trustee pursuant to Section
3.7.

     "Stated Maturity," when used with respect to any Security or any
      ---------------
installment of principal thereof or interest thereon, means the date specified
in such Security as the fixed date on which the principal of such Security or
such installment of principal or interest is due and payable.

     "Subsidiary" means any corporation of which the Company at the time owns or
      ----------
controls, directly or indirectly, more than 50% of the shares of outstanding
stock having general voting power under ordinary circumstances to elect a
majority of the Board of Directors of such corporation (irrespective of whether
or not at the time stock of any other class or classes of such corporation shall
have or might have voting power by reason of the happening of any contingency).

     "Trustee" means the party named as such in the first paragraph of this
      -------
Indenture until a successor Trustee replaces it pursuant to the applicable
provisions of this Indenture, and thereafter means such successor Trustee and
if, at any time, there is more than one Trustee, "Trustee" as used with respect
to the Securities of any series shall mean the Trustee with respect to the
Securities of that series.

     "Trust Indenture Act" means the Trust Indenture Act of 1939, as amended, as
      -------------------
in effect on the date of this Indenture, except as provided in Section 8.3.

     "Yield to Maturity" means the yield to maturity, calculated by the Company
      -----------------
at the time of issuance of a series of Securities or, if applicable, at the most
recent determination of interest on such series, in accordance with accepted
financial practice.

     (b)  The following terms shall have the meanings specified in the Sections
referred to opposite such term below:

                                      -6-
<PAGE>

           Term                              Section
           ----                              -------
     "Act"                                    1.4(a)
     "Bankruptcy Law"                         5.1
     "Custodian"                              5.1
     "Defaulted Interest"                     3.7(b)
     "Event of Default"                       5.1
     "Register"                               3.5
     "Registrar"                              3.5
     "Valuation Date"                         3.7(c)

Section 1.2    Compliance Certificates and Opinions

     Upon any application or request by the Company to the Trustee to take any
action under any provision of this Indenture, the Company shall furnish to the
Trustee an Officers' Certificate stating that all conditions precedent, if any,
provided for in this Indenture relating to the proposed action have been
complied with and an Opinion of Counsel stating that in the opinion of such
counsel all such conditions precedent, if any, have been complied with, except
that in the case of any such application or request as to which the furnishing
of such documents is specifically required by any provision of this Indenture
relating to such particular application or request, no additional certificate or
opinion need be furnished.

     Every certificate or opinion with respect to compliance with a condition or
covenant provided for in this Indenture (other than pursuant to Sections 2.3,
3.3 and 9.7) shall include:

          (1)  a statement that each individual signing such certificate or
     opinion has read such condition or covenant and the definitions herein
     relating thereto;

          (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 each such individual, he has
     made such examination or investigation as is necessary to enable him to
     express an informed opinion as to whether or not such condition or covenant
     has been complied with; and

          (4)  a statement as to whether, in the opinion of each such
     individual, such condition or covenant has been complied with.

Section 1.3    Form of Document Delivered to Trustee

     In any case where several matters are required to be certified by, or
covered by an opinion of, any specified Person, it is not necessary that all
such matters be certified by, or covered by the opinion of, only one such
Person, or that they be so certified or covered by only one document, but one
such Person may certify or give an opinion with respect to some

                                      -7-
<PAGE>

matters and one or more other such Persons as to other matters, and any such
Person may certify or give an opinion as to such matters in one or several
documents.

     Any certificates or opinions of an officer of the Company may be based,
insofar as it relates to legal matters, upon a certificate or opinion of, or
representations by, counsel, unless such officer knows, or in the exercise of
reasonable care should know, that the certificate or opinion or representations
with respect to the matters upon which his certificate or opinion is based are
erroneous.  Any such certificate or Opinion of Counsel may be based, insofar as
it relates to factual matters, upon a certificate or opinion of, or
representations by, an officer or officers of the Company stating that the
information with respect to such factual matters is in the possession of the
Company, unless such counsel knows, or in the exercise of reasonable care should
know, that the certificate or opinion or representations as to such matters are
erroneous.

     Where any Person is required to make, give or execute two or more
applications, requests, consents, certificates, statements, opinions or other
instruments under this Indenture, they may, but need not, be consolidated and
form one instrument.

Section 1.4    Acts of Holders

     (a)  Any request, demand, authorization, direction, notice, consent, waiver
or other action provided by this Indenture to be given or taken by Holders may
be embodied in and evidenced by one or more instruments of substantially similar
tenor signed by such Holders in person or by agent duly appointed in writing.
Except as herein otherwise expressly provided, such action shall become
effective when such instrument or instruments are delivered to the Trustee and,
where it is hereby expressly required, to the Company.  Such instrument or
instruments (and the action embodied therein and evidenced thereby) are herein
sometimes referred to as the "Act" of the Holders signing such instrument or
instruments.  Proof of execution of any such instrument or of a writing
appointing any such agent shall be sufficient for any purpose of this Indenture
and conclusive in favor of the Trustee and the Company, if made in the manner
provided in this Section.

     (b)  The fact and date of the execution by any Person of any such
instrument or writing may be proved by the affidavit of a witness of such
execution or by a certificate of a notary public or other officer authorized by
law to take acknowledgments of deeds, certifying that the individual signing
such instrument or writing acknowledged to him the execution thereof. Where such
execution is by a signer acting in a capacity other than his individual
capacity, such certificate or affidavit shall also constitute sufficient proof
of his authority. The fact and date of the execution of any such instrument or
writing, or the authority of the Person executing the same, may also be proved
in any other reasonable manner which the Trustee deems sufficient.

     (c)  The ownership of Securities shall be proved by the Register.

                                      -8-
<PAGE>

     (d)  Any request, demand, authorization, direction, notice, consent, waiver
or other Act of the Holder of any Security shall bind every future Holder of the
same Security and the holder of every Security issued upon the registration of
transfer thereof or in exchange therefor or in lieu thereof in respect of
anything done, omitted or suffered to be done by the Trustee or the Company in
reliance thereon, whether or not notation of such action is made upon such
Security.

     (e)  If the Company shall solicit from the Holders any request, demand,
authorization, direction, notice, consent, waiver or other Act, the Company may,
at its option, by or pursuant to an Officers' Certificate delivered to the
Trustee, fix in advance a record date for the determination of Holders entitled
to give such request, demand, authorization, direction, notice, consent, waiver
or other Act, but the Company shall have no obligation to do so.  If such a
record date is fixed, such request, demand, authorization, direction, notice,
consent, waiver or other Act may be given before or after such record date, but
only the Holders of record at the close of business on such record date shall be
deemed to be Holders for the purposes of determining whether Holders of the
requisite proportion of Outstanding Securities have authorized or agreed to
consented to such request, demand, authorization, direction, notice, consent,
waiver or other Act, and for that purpose the Outstanding Securities shall be
computed as of such record date; provided that no such authorization, agreement
                                 --------
or consent by the Holders on such record date shall be deemed effective unless
it shall become effective pursuant to the provisions of clause (a) of this
Section 1.4 not later than six months after the record date.

Section 1.5    Notices, etc., to Trustee and Company

     Any request, demand, authorization, direction, notice, consent, waiver or
Act of Holders or other document provided or permitted by this Indenture to be
made upon, given or furnished to, or filed with,

          (1)  the Trustee by any Holder or by the Company shall be sufficient
     for every purpose hereunder if made, given, furnished or filed in writing
     to or with the Trustee at its Corporate Trust Office, Attention:  Corporate
     Trust Trustee Administration, or

          (2)  the Company by the Trustee or by any Holder shall be sufficient
     for every purpose hereunder (unless otherwise herein expressly provided) if
     in writing and mailed, first-class postage prepaid, to the Company
     addressed to it at ICOS Corporation, 22021 -- 20th Avenue Southeast,
     Bothell, Washington 98021, Attention:  Corporate Secretary or at any other
     address previously furnished in writing to the Trustee by the Company.

Section 1.6    Notice to Holders; Waiver

     Where this Indenture provides for notice to Holders of any event, such
notice shall be sufficiently given (unless otherwise herein expressly provided
or otherwise agreed to by a

                                      -9-
<PAGE>

Holder) if in writing and mailed, first-class postage prepaid, to each Holder
affected by such event, at his address as it appears in the Register, within the
time prescribed for the giving of such notice.

     In any case where notice to Holders is given by mail, neither the failure
to mail such notice, nor any defect in any notice so mailed, to any particular
Holder shall affect the sufficiency of such notice with respect to other
Holders.  Any notice mailed to a Holder in the manner herein prescribed shall be
conclusively deemed to have been received by such Holder, whether or not such
Holder actually receives such notice.

     If by reason of the suspension of regular mail service or by reason of any
other cause it shall be impracticable to give such notice as provided above,
then such notification as shall be made with the approval of the Trustee shall
constitute a sufficient notification for every purpose hereunder.

     Where this Indenture provides for notice in any manner, such notice may be
waived in writing by the Person entitled to receive such notice, either before
or after the event, and such waiver shall be equivalent of such notice.  Waivers
of notice by Holders shall be filed with the Trustee, but such filing shall not
be a condition precedent to the validity of any action taken in reliance upon
such waiver.

Section 1.7    Headings and Table of Contents

     The Article and Section headings herein and the Table of Contents are for
convenience only and shall not affect the construction hereof.

Section 1.8    Successors and Assigns

     All covenants and agreements in this Indenture by the Company shall bind
its successors and assigns, whether so expressed or not.

Section 1.9    Separability

     In case any provision of this Indenture or 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.

Section 1.10   Benefits of Indenture

     Nothing in this Indenture or in the Securities, expressed or implied, shall
give to any Person, other than the parties hereto and their successors hereunder
and the Holders, any benefit or any legal or equitable right, remedy or claim
under this Indenture.

                                      -10-
<PAGE>

Section 1.11  Governing Law

     THIS INDENTURE AND THE SECURITIES SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK. This Indenture is subject to
the Trust Indenture Act and if any provision hereof limits, qualifies or
conflicts with the Trust Indenture Act, the Trust Indenture Act shall control.

Section 1.12  Legal Holidays

     In any case where any Interest Payment Date, Redemption Date, sinking fund
payment date, Stated Maturity or Maturity of any Security shall not be a
Business Day at any Place of Payment, then (notwithstanding any other provision
of this Indenture of any Security other than a provision in the Securities of
any series which specifically states that such provision shall apply in lieu of
this Section) payment of principal, premium, if any, or interest need not be
made at such Place of Payment on such date, but may be made on the next
succeeding Business Day at such Place of Payment with the same force and effect
as if made on such date; provided that no interest shall accrue on the amount so
                         --------
payable for the period from and after such Interest Payment Date, Redemption
Date, sinking fund payment date, Stated Maturity or Maturity, as the case may
be.

                                   ARTICLE 2


                                Security Forms

Section 2.1  Forms Generally

     The Securities of each series shall be in substantially the form set forth
in this Article, or in such other form or forms as shall be established by
delivery to the Trustee of an Officers' Certificate or in one or more indentures
supplemental hereto, in each case with such appropriate insertions, omissions,
substitutions and other variations as are required or permitted by this
Indenture, and may have such letters, numbers or other marks of identification
and such legends or endorsements placed thereon as may be required to comply
with the rules of any securities exchange or as may, consistently herewith, be
determined by the officers executing such Securities as evidenced by their
execution of the Securities.  If temporary Securities of any series are issued
as permitted by Section 3.4, the form thereof also shall be established as
provided in the preceding sentence.  If the form of Securities of any series are
established by an Officers' Certificate, such Officers' Certificate shall be
delivered to the Trustee at or prior to the delivery of the Company Order
contemplated by Section 3.3 for the authentication and delivery of such
Securities.

     The permanent Securities shall be printed, lithographed or engraved or
produced by any combination of these methods or may be produced in any other
manner, all as determined by the officers executing such Securities as evidenced
by their execution of such Securities.

                                      -11-
<PAGE>

Section 2.2  Form of Face of Security

     [If the Security is an Original Issue Discount Security, insert--FOR
      --------------------------------------------------------------
PURPOSES OF SECTIONS 1273 AND 1275 OF THE UNITED STATES INTERNAL REVENUE CODE,
THE AMOUNT OF ORIGINAL ISSUE DISCOUNT ON THIS SECURITY IS    % OF ITS PRINCIPAL
AMOUNT AND THE ISSUE DATE IS        , 200  [, -- AND] THE YIELD TO MATURITY IS
_____%.  [THE METHOD USED TO DETERMINE THE YIELD IS ________________ AND THE
AMOUNT OF ORIGINAL ISSUE DISCOUNT APPLICABLE TO THE SHORT ACCRUAL PERIOD OF
_______________, 200__TO ____________________, 200__IS ___% OF THE PRINCIPAL
AMOUNT OF THIS SECURITY.]]

                                ICOS CORPORATION

$                                                                     No.

     ICOS CORPORATION, a corporation duly organized and existing under the laws
of the State of Delaware (herein called the "Company," which term includes any
successor corporation under the Indenture hereinafter referred to), for value
received, hereby promises to pay to

or registered assigns, the principal sum of                             Dollars
on                   [If the Security is to bear interest prior to Maturity,
                      ------------------------------------------------------
insert--, and to pay interest thereon from          or from the most recent
------
Interest Payment Date to which interest has been paid or duly provided for,
semiannually on           and                in each year, commencing         ,
[If the Security is to bear interest at a fixed rate, insert--at the rate of
 -----------------------------------------------------------
% per annum] [if the Security is to bear interest at an adjustable rate, insert-
              -----------------------------------------------------------------
-at a rate per annum computed or determined in accordance with the provisions
below], until the principal hereof is paid or made available for payment [If
                                                                          --
applicable, insert--, and (to the extent that the payment of such interest shall
------------------
be legally enforceable) at the rate of    % per annum on any overdue principal
and premium and on any overdue installment of interest].  The interest so
payable, and punctually paid or duly provided for, on any Interest Payment Date
will, as provided in such Indenture, be paid to the Person in whose name this
Security (or one or more Predecessor Securities) is registered at the close of
business on the Regular Record Date for such interest, which shall be the     or
(whether or not a Business Day), as the case may be, next preceding such
Interest Payment Date.  Any such interest not so punctually paid or duly
provided for will forthwith cease to be payable to the Holder on such Regular
Record Date and may either be paid to the Person in whose name this Security (or
one or more Predecessor Securities) is registered at the close of business on a
Special Record Date for the payment of such Defaulted Interest to be fixed by
the Trustee, notice whereof shall be given to Holders of Securities of this
series not less than 10 days prior to such Special Record Date, or be paid at
any time in any other lawful manner not inconsistent with the requirements of
any securities exchange on which the Securities of this series may be listed,
and upon such notice as may be required by such exchange, all as more fully
provided in said Indenture].

                                      -12-
<PAGE>

     [If the Security is not to bear interest prior to Maturity, insert--The
      -----------------------------------------------------------------
principal of this Security shall not bear interest except in the case of a
default in payment of principal upon acceleration or redemption or at the Stated
Maturity and in such case the overdue principal of this Security shall bear
interest at the rate of       % per annum (to the extent that the payment of
such interest shall be legally enforceable), which shall accrue from the date of
such default in payment to the date payment of such principal has been made or
duly provided for.  Interest on any overdue principal shall be payable on
demand.  Any such interest on any overdue principal that is not so paid on
demand shall bear interest at the rate of           % per annum (to the extent
that the payment of such interest shall be legally enforceable), which shall
accrue from the date of such demand for payment to the date payment of such
interest has been made or duly provided for, and such interest shall also be
payable on demand.]

     Payment of the principal of (and premium, if any, on) and [if applicable,
                                                                --------------
insert--any such] interest on this Security will be made at the office or agency
------
of the Company maintained for that purpose in the City and State of New York in
such coin or currency of the United States of America as at the time of payment
is legal tender for payment of public and private debts [if applicable, insert--
                                                         ---------------------
; provided, however, that at the option of the Company payment of interest may
  --------  -------
be made by check mailed on or before the relevant Interest Payment Date to the
address of the Person entitled thereto as such address shall appear in the
Register].

     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.

     Unless the certificate of authentication hereon has been executed by the
Trustee referred to on the reverse hereof by manual signature, this Security
shall not be entitled to any benefit under the Indenture or be valid or
obligatory for any purpose.

     IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed.

     Dated:

                              ICOS CORPORATION


                              By __________________________________

     Attest:

Section 2.3  Form of Reverse of Security

     This Security is one of a duly authorized issue of securities of the
Company (herein called the "Securities") issued and to be issued in one or more
series under an Indenture, dated as of ___________, 200__ (herein called the
"Indenture"), between the Company (which term includes any successor corporation
under the Indenture) and _________________________,

                                      -13-
<PAGE>

as Trustee (herein called the "Trustee," which term includes any successor
trustee under the Indenture with respect to the series of which this Security is
a part), to which the Indenture and all indentures supplemental thereto
reference is hereby made for a statement of the respective rights, limitations
of rights, duties and immunities thereunder of the Company, the Trustee and the
Holders of the Securities and of the terms upon which the Securities are, and
are to be, authenticated and delivered. This Security is one of the series
designated on the face hereof[, limited in aggregate principal amount to $    ].

[If applicable, insert--The Securities of this series are subject to redemption
 ---------------------
upon not less than 30 days' notice by mail, [if applicable, insert--(1) on
                                             ---------------------
___________ in any year commencing with the year __________ and ending with the
year _________ at a Redemption Price equal to     % of the principal amount and
(2)] at any time [on or after 200__], as a whole or in part, at the election of
the Company, at the following Redemption Prices (expressed as percentages of the
principal amount):  If redeemed [on or before ______, ___%, and if redeemed]
during the 12-month period beginning _________ of the years indicated,


        Year     Redemption Price         Year         Redemption Price
        ----     ----------------         ----         ----------------





and thereafter at a Redemption Price equal to __% of the principal amount,
together in the case of any such redemption with accrued interest to the
Redemption Date, but interest installments whose Stated Maturity is on or prior
to such Redemption Date will be payable to the Holders of such Securities, or
one or more Predecessor Securities, of record at the close of business on the
relevant Regular Record Dates referred to on the face hereof, all as provided in
the Indenture.]

[If applicable, insert--The Securities of this series are subject to redemption
 ---------------------
upon not less than 30 days' notice by mail, (1) on ___________ in any year
commencing with the year ____________ and ending with the year _________ through
operation of the sinking fund for this series at the Redemption Prices for
redemption through operation of the sinking fund (expressed as percentages of
the principal amount) set forth in the table below and (2) at any time [on or
after ____________], as a whole or in part, at the election of the Company, at
the Redemption Prices for redemption otherwise than through operation of the
sinking fund (expressed as percentages of the principal amount) set forth in the
table below:  If redeemed during the 12-month period beginning _____________ of
the years indicated,

          Redemption Price for Redemption       Redemption Price for Redemption
              Through Operation of the         Otherwise Than Through Operation
 Year               Sinking Fund                      of the Sinking Fund
 ----     -------------------------------      ---------------------------------




                                      -14-
<PAGE>

and thereafter at a Redemption Price equal to ____% of the principal amount,
together in the case of any such redemption (whether through operation of the
sinking fund or otherwise) with accrued interest to the Redemption Date, but
interest installments whose Stated Maturity is on or prior to such Redemption
Date will be payable to the Holders of such Securities, or one or more
Predecessor Securities, of record at the close of business on the relevant
Regular Record Dates referred to on the face hereof, all as provided in the
Indenture.]

     [Notwithstanding the foregoing, the Company may not, prior to __________,
redeem any Securities of this series as contemplated by [Clause (2) of] the
preceding paragraph as a part of, or in anticipation of, any refunding operation
by the application, directly or indirectly, of moneys borrowed having an
interest cost to the Company (calculated in accordance with generally accepted
financial practice) of less than ___% per annum.]

     [The sinking fund for this series provides for the redemption on __________
in each year beginning with the year _______________ and ending with the year
____________ of [not less than] $____________ [("mandatory sinking fund")] and
not more than $____________ aggregate principal amount of Securities of this
series.  [Securities of this series acquired or redeemed by the Company
otherwise than through [mandatory] sinking fund payments may be credited against
subsequent [mandatory] sinking fund payments otherwise required to be made in
the [describe order] order in which they become due.]]
     --------------

     [In the event of redemption of this Security in part only, a new Security
or Securities of this series for the unredeemed portion hereof will be issued in
the name of the Holder hereof upon the cancellation hereof.]

     [If applicable, insert--The Securities of this series are subject to the
      ---------------------
covenant defeasance provisions set forth in Article Four of the Indenture.]

     [If the Security is not an Original Issue Discount Security, insert--If an
      ------------------------------------------------------------------
Event of Default with respect to Securities of this series shall occur and be
continuing, the principal of the Securities of this series may be declared due
and payable in the manner and with the effect provided in the Indenture.]

     [If the Security is an Original Issue Discount Security, insert--If an
      --------------------------------------------------------------
Event of Default with respect to Securities of this series shall occur and be
continuing, an amount of principal of the Securities of this series may be
declared due and payable in the manner and with the effect provided in the
Indenture.  Such amount shall be equal to--insert formula for determining the
                                           ----------------------------------
amount.  Upon payment (i) of the amount of principal so declared due and payable
------
and (ii) of interest on any overdue principal and overdue interest (in each case
to the extent that the payment of such interest shall be legally enforceable),
all the Company's obligations in respect of the payment of the principal of and
interest, if any, on the Securities of this series shall terminate.]

                                      -15-
<PAGE>

     The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Holders of the Securities of each series to be
affected under the Indenture at any time by the Company and the Trustee with the
consent of the Holders of a majority in principal amount of the Outstanding
Securities of each series to be affected.  The Indenture also contains
provisions permitting the Holders of specified percentages in principal amount
of the Outstanding Securities of each series, on behalf of the Holders of all
Outstanding Securities of such series, to waive compliance by the Company with
certain provisions of the Indenture and certain past defaults under the
Indenture and their consequences.  Any such consent or waiver by the Holder of
this Security shall be conclusive and binding upon such Holder and upon all
future Holders of this Security and of any Security issued upon the registration
of transfer hereof or in exchange or in lieu hereof, whether or not notation of
such consent or waiver is made upon this Security.

     No reference herein to the Indenture and no provision of this Security or
of the Indenture shall alter or impair the obligation of the Company, which is
absolute and unconditional, to pay the amount of principal of (and premium, if
any, on) and interest, if any, on this Security herein provided, and at the
times, place and rate, and in the coin or currency, herein prescribed.

     As provided in the Indenture and subject to certain limitations therein set
forth, the transfer of this Security is registrable in the Security Register,
upon surrender of this Security for registration of transfer at the office or
agency of the Company in any place where the principal of (and premium, if any,
on) and interest, if any, on this Security are payable, duly endorsed by, or
accompanied by a written instrument of transfer in form satisfactory to the
Company and the Security Registrar duly executed by, the Holder hereof or his
attorney duly authorized in writing, and thereupon one or more new Securities of
this series, of authorized denominations and for the same aggregate principal
amount, will be issued to the designated transferee or transferees.

     The Securities of this series are issuable only in registered form without
coupons in denominations of $___________ and any integral multiple thereof.  As
provided in the Indenture and subject to certain limitations therein set forth,
Securities of this series are exchangeable for a like aggregate principal amount
of Securities of this series of different authorized denominations as requested
by the Holder surrendering the same.

     No service charge shall be made for any such registration of transfer or
exchange, but the Company may require payment of a sum sufficient to cover any
tax or other governmental charge payable in connection therewith.

     Prior to due presentment of this Security for registration of transfer, the
Company, the Trustee and any agent of the Company or the Trustee may treat the
Person in whose name this Security is registered as the owner hereof for all
purposes, whether or not this Security be overdue, and neither the Company nor
the Trustee nor any such agent shall be affected by notice to the contrary.

                                      -16-
<PAGE>

All terms used in this Security which are defined in the Indenture shall have
the meanings assigned to them in the Indenture.

Section 2.4  Form of Trustee's Certificate of Authentication

     The Trustee's certificate of authentication shall be in substantially the
following form:

     This is one of the Securities of a series issued under the within-mentioned
Indenture.

                                          ___________________________,
                                                           as Trustee


                                          By_______________________________
                                              Authorized Signatory

                                   ARTICLE 3


                                The Securities

Section 3.1  Amount Unlimited; Issuable in Series

     (a)  The aggregate principal amount of Securities which may be
authenticated and delivered under this Indenture is unlimited. The Securities
may be issued from time to time in one or more series.

     (b)  The following matters shall be established and (subject to Section
3.3) set forth, or determined in the manner provided, in an Officers'
Certificate and a Board Resolution of the Company or one or more indentures
supplemental hereto:

          (1)  the title of the Securities of the series (which title shall
     distinguish the Securities of the series from all other Securities);

          (2)  any limit upon the aggregate principal amount of the Securities
     of the series which may be authenticated and delivered under this Indenture
     (which limit shall not pertain to (i) Securities authenticated and
     delivered upon registration of transfer of, or in exchange for, or in lieu
     of, other Securities of the series pursuant to Section 3.4, 3.5, 3.6, 8.6,
     or 10.7 and (ii) any Securities which, pursuant to the last paragraph of
     Section 3.3, are deemed never to have been authenticated and delivered
     thereunder);

          (3)  the date or dates on which the principal of the Securities of the
     series is payable or the method of determination thereof;

          (4)  the rate or rates at which the Securities of the series shall
     bear interest, if any, or the method of calculating such rate or rates of
     interest, the date or dates from

                                      -17-
<PAGE>

     which such interest shall accrue or the method by which such date or dates
     shall be determined, the Interest Payment Dates on which any such interest
     shall be payable and the Regular Record Date, if any, for the interest
     payable on any Interest Payment Date;

          (5)  the place or places where, subject to the provisions of Section
     9.2, the principal of, premium, if any, and interest, if any, on Securities
     of the series shall be payable;

          (6)  the period or periods within which, the price or prices at which,
     and the other terms and conditions upon which, Securities of the series may
     be redeemed, in whole or in part, at the option of the Company and, if
     other than as provided in Section 10.3, the manner in which the particular
     Securities of such series (if less than all Securities of such series are
     to be redeemed) are to be selected for redemption;

          (7)  the obligation, if any, of the Company to redeem or purchase
     Securities of the series pursuant to any sinking fund or analogous
     provisions or upon the happening of a specified event or at the option of a
     Holder thereof and the period or periods within which, the price or prices
     at which, and the other terms and conditions upon which, Securities of the
     series shall be redeemed or purchased, in whole or in part, pursuant to
     such obligation;

          (8)  if other than denominations of $1,000 and any integral multiple
     thereof, the denominations in which Securities of the series shall be
     issuable;

          (9)  if the amount of payments or principal of, premium, if any, and
     interest, if any, on the Securities of the series shall be determined with
     reference to an index, formula or other method, the index, formula or other
     method by which such amounts shall be determined;

          (10) if other than the principal amount thereof, the portion of the
     principal amount of such Securities of the series which shall be payable
     upon declaration of the acceleration thereof pursuant to Section 5.2 or the
     method by which such portion shall be determined;

          (11) if other than as provided in Section 3.7, the Person to whom any
     interest on any Security of the series shall be payable and the extent to
     which, or the manner in which (including any certification requirement and
     other terms and conditions under which), any interest payable on a
     temporary Security on an Interest Payment Date will be paid if other than
     in the manner provided in Section 3.4, as applicable;

          (12) provisions, if any, granting special rights to the Holders of
     Securities of the series upon the occurrence of such events as may be
     specified;

                                      -18-
<PAGE>

          (13) any deletions from, modifications of or additions to the Events
     of Default set forth in Section 5.1 or covenants of the Company set forth
     in Article 9 pertaining to the Securities of the series;

          (14) under what circumstances, if any, the Company will pay additional
     amounts on the Securities of that series held by a Person who is not a U.S.
     Person in respect of taxes or similar charges withheld or deducted and, if
     so, whether the Company will have the option to redeem such Securities
     rather than pay such additional amounts (and the terms of any such option);

          (15) the date as of which any temporary Security representing
     outstanding Securities of the series shall be dated if other than the date
     of original issuance of the first Security of the series to be issued;

          (16) the applicability, if any, to the Securities of or within the
     series of Sections 4.4 and 4.5, or such other means of defeasance or
     covenant defeasance as may be specified for the Securities of such series;

          (17) if other than the Trustee, the identity of the Registrar and any
     Paying Agent;

          (18) any terms which may be related to warrants issued by the Company
     in connection with, or for the purchase of, Securities of such series,
     including whether and under what circumstances the Securities of any series
     may be used toward the exercise price of any such warrants; and

          (19) any other terms of the series (which terms shall not be
     inconsistent with the provisions of this Indenture), including any terms
     which may be required by or advisable under United States laws or
     regulations or advisable in connection with the marketing of Securities of
     the series.

     (c)  All Securities of any one series shall be substantially identical
except as to denomination and the rate or rates of interest, if any, and Stated
Maturity, the date from which interest, if any, shall accrue and except as may
otherwise be provided in or pursuant to an Officers' Certificate pursuant to
this Section 3.1 or in an indenture supplemental hereto.  All Securities of any
one series need not be issued at the same time and, unless otherwise provided, a
series may be reopened, without the consent of the Holders, for issuances of
additional Securities of such series or for the establishment of additional
terms with respect to the Securities of such series.

     (d)  If any of the terms of the Securities of any series are established by
action taken pursuant to a Board Resolution, a copy of such Board Resolution
shall be certified by the Corporate Secretary or an Assistant Secretary of the
Company and delivered to the Trustee at or prior to the delivery of the
Officers' Certificate setting forth, or providing the manner for determining,
the terms of the Securities of such series, and an appropriate record of any
action taken pursuant thereto in connection with the issuance of any Securities
of such series shall be

                                      -19-
<PAGE>

delivered to the Trustee prior to the authentication and delivery thereof. With
respect to Securities of a series subject to a Periodic Offering, such Board
Resolution or Officers' Certificate may provide general terms for Securities of
such series and provide either that the specific terms of particular Securities
of such series shall be specified in a Company Order or that such terms shall be
determined by the Company, or one or more of the Company's agents designated in
an Officers' Certificate, in accordance with the Company Order as contemplated
by the first proviso of the third paragraph of Section 3.3

Section 3.2  Denominations

     The Securities of each series shall be issuable only in definitive
registered form without coupons and in such denominations as shall be specified
as contemplated by Section 3.1.  In the absence of any such provisions with
respect to the Securities of any series, the Securities of such series shall be
issuable in denominations of $1,000 and any integral multiple thereof.

Section 3.3  Execution, Authentication, Delivery and Dating

     Securities shall be executed on behalf of the Company by the Chairman,
President or Chief Executive Officer and attested to by the Secretary of the
Company.  The Company's seal shall be affixed to the Securities, or a facsimile
of such seal shall be engraved, printed, or otherwise reproduced on the
Securities.  The signatures of such officers on the Securities may be manual or
facsimile signatures of the present or any future such authorized officers and
may be imprinted or otherwise reproduced on the Securities.

     Securities bearing the manual or facsimile signatures of individuals who
were at any time the proper officers of the Company shall bind the Company,
notwithstanding that such individuals or any of them have ceased to hold such
offices prior to the authentication and delivery of such Securities or did not
hold such offices at the date of such Securities.

     At any time and from time to time, the Company may deliver Securities of
any series executed by the Company to the Trustee for authentication, together
with a Company Order for the authentication and make available for delivery such
Securities, and the Trustee in accordance with the Company Order shall
authenticate and deliver such Securities; provided, however, that in the case of
                                          --------  -------
Securities offered in a Periodic Offering, the Trustee shall authenticate and
deliver such Securities from time to time in accordance with such other
procedures (including, without limitation, the receipt by the Trustee of oral or
electronic instructions from the Company or its duly authorized agents, promptly
confirmed in writing) acceptable to the Trustee as may be specified by or
pursuant to a Company Order delivered to the Trustee prior to the time of the
first authentication of Securities of such series.

     If the form or terms of the Securities of a series have been established by
or pursuant to one or more Officers' Certificates as permitted by Sections 2.1
and 3.1, in authenticating such Securities and accepting the additional
responsibilities under this Indenture in relation to such Securities, the
Trustee shall be entitled to receive, and (subject to section 315(a) through

                                      -20-
<PAGE>

(d) of the Trust Indenture Act) shall be fully protected in relying upon, an
Opinion of Counsel stating,

               (1)  that the forms and terms of such Securities have been
          established in conformity with the provisions of this Indenture; and

               (2)  that such Securities, when authenticated and delivered by
          the Trustee and issued by the Company in the manner and subject to any
          conditions specified in such Opinion of Counsel, will constitute valid
          and legally binding obligations of the Company, enforceable in
          accordance with their terms, subject to customary exceptions;

provided, however, that, with respect to Securities of a series subject to a
--------  -------
Periodic Offering, the Trustee shall be entitled to receive such Opinion of
Counsel only once at or prior to the time of the first authentication of
Securities of such series and that the Opinion of Counsel above may state:

               (x)  that the forms of such Securities have been, and the terms
          of such Securities (when established in accordance with such
          procedures as may be specified from time to time in a Company Order,
          all as contemplated by and in accordance with a Board Resolution or an
          Officers' Certificate pursuant to Section 3.1, as the case may be)
          will have been, established in conformity with the provisions of this
          Indenture; and

               (y)  that such Securities, when (1) executed by the Company, (2)
          completed, authenticated and delivered by the Trustee in accordance
          with this Indenture, and (3) issued by the Company in the manner and
          subject to any conditions specified in such Opinion of Counsel, will
          constitute valid and legally binding obligations of the Company,
          enforceable in accordance with their terms, subject to customary
          exceptions.

          With respect to Securities of a series subject to a Periodic Offering,
the Trustee may conclusively rely, as to the authorization by the Company of any
of such Securities, the form and terms thereof and the legality, validity,
binding effect and enforceability thereof, upon the Opinion of Counsel and other
documents delivered pursuant to Sections 2.1 and 3.1 of this Section, as
applicable, at or prior to the time of the first authentication of Securities of
such series unless and until it has received written notification that such
opinion or other documents have been superseded or revoked. In connection with
the authentication and delivery of Securities of a series subject to a Periodic
Offering, the Trustee shall be entitled to assume that the Company's
instructions to authenticate and deliver such Securities do not violate any
rules, regulations or orders of any governmental agency or commission having
jurisdiction over the Company.

          If the form or terms of the Securities of a series have been
established by or pursuant to one or more Officers' Certificates as permitted by
Sections 2.1 and 3.1, the Trustee shall have the right to decline to
authenticate such Securities if the issue of such Securities pursuant

                                      -21-
<PAGE>

to this Indenture will adversely affect the Trustee's own rights, duties or
immunities under this Indenture or otherwise in a manner which is not reasonably
acceptable to the Trustee.

          Notwithstanding the provisions of Section 3.1 and of the two preceding
paragraphs, if all of the Securities of any series are not to be issued at one
time, it shall not be necessary to deliver the Officers' Certificate otherwise
required pursuant to Section 3.1 at or prior to the time of the authentication
of each Security of such series if the Officers' Certificate is delivered at or
prior to the authentication upon original issuance of the first Security of such
series to be issued.

          Each Security shall be dated the date of its authentication.

          No Security shall be entitled to any benefits under this Indenture or
be valid or obligatory for any purpose until authenticated by the manual
signature of one of the authorized signatories of the Trustee or an
Authenticating Agent. Such signature upon any Security shall be conclusive
evidence, and the only evidence, that such Security has been duly authenticated
and delivered under this Indenture and is entitled to the benefits of this
Indenture.

          Notwithstanding the foregoing, if any Security shall have been
authenticated and delivered hereunder but never issued and sold by the Company,
and the Company shall deliver such Security to the Trustee for cancellation as
provided in Section 3.9 together with a written statement (which need not comply
with Section 1.2 and need not be accompanied by an Opinion of Counsel) stating
that such Security has never been issued and sold by the Company, for all
purposes of this Indenture such Security shall be deemed never to have been
authenticated and delivered hereunder and shall not be entitled to the benefits
of this Indenture.

Section 3.4    Temporary Securities

          Pending the preparation of definitive Securities of any series, the
Company may execute and, upon Company Order, the Trustee shall authenticate and
deliver temporary Securities of such series which are printed, lithographed,
typewritten, mimeographed or otherwise produced, in any authorized denomination,
substantially of the tenor and form of the definitive Securities in lieu of
which they are issued and with such appropriate insertions, omissions,
substitutions and other variations as the officers executing such Securities may
determine, as conclusively evidenced by their execution of such Securities.

          If temporary Securities of any series are issued, the Company will
cause permanent Securities of such series to be prepared without unreasonable
delay. After preparation of such permanent Securities, the temporary Securities
shall be exchangeable for such permanent Securities of like tenor upon surrender
of the temporary Securities of such series at the office or agency of the
Company pursuant to Section 9.2 in a Place of Payment for such series, without
charge to the Holder. Upon surrender for cancellation of any one or more
temporary Securities of any series, the Company shall execute and the Trustee
shall authenticate and deliver in exchange therefor a like principal amount of
Permanent Securities of the same

                                      -22-
<PAGE>

series of authorized denominations and of like tenor. Until so exchanged, the
temporary Securities of any series shall in all respects be entitled to the same
benefits under this Indenture as permanent Securities of such series except as
otherwise specified as contemplated by Section 3.1.

Section 3.5    Registration, Registration of Transfer and Exchange

          The Company shall cause to be kept at the Corporate Trust Office of
the Trustee or in any office or agency to be maintained by the Company in
accordance with Section 9.2 in a Place of Payment a register (the "Register") in
which, subject to such reasonable regulations as it may prescribe, the Company
shall provide for the registration of Securities and the registration of
transfers of Securities. The Register shall be in written form or any other form
capable of being converted into written form within a reasonable time. The
Trustee is hereby appointed "Registrar" for the purpose of registering
Securities and transfers of Securities as herein provided.

          Upon surrender for registration of transfer of any Security of any
series at the office or agency maintained pursuant to Section 9.2 in a Place of
Payment for that series, the Company shall execute, and the Trustee shall
authenticate and deliver, in the name of the designated transferee or
transferees, one or more new Securities of the same series, of any authorized
denominations and of a like aggregate principal amount and tenor.

          At the option of the Holder, Securities of any series may be exchanged
for other Securities of the same series, of any authorized denominations and of
like aggregate principal amount containing identical terms and provisions, upon
surrender of the Securities to be exchanged at such office or agency. Whenever
any Securities are so surrendered for exchange, the Company shall execute, and
the Trustee shall authenticate and deliver, the Securities which the Holder
making the exchange is entitled to receive.

          Whenever any Securities are surrendered for exchange, the Company
shall execute, and the Trustee shall authenticate and deliver, the Securities
which the Holder making the exchange is entitled to receive.

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

          Every Security presented or surrendered for registration of transfer
or for exchange shall (if so required by the Company, the Registrar or the
Trustee) be duly endorsed, or be accompanied by a written instrument of transfer
in form satisfactory to those of the Company, the Registrar and the Trustee
requiring such written instrument of transfer duly executed by the Holder
thereof or his attorney duly authorized in writing.

          No service change shall be made for any registration of transfer or
for any exchange of Securities, but the Company may require payment of a sum
sufficient to cover any tax or other

                                      -23-
<PAGE>

governmental charge that may be imposed in connection with any registration or
transfer or exchange of Securities, other than exchanges pursuant to Section 3.4
or 10.7 not involving any transfer.

          The Company shall not be required (i) to issue, register the transfer
of, or exchange any Securities for a period beginning at the opening of business
15 days before any selection for redemption of Securities of like tenor and of
the series of which such Security is a part and ending at the close of business
on the earliest date on which the relevant notice of redemption is deemed to
have been given to all Holders of Securities of like tenor and of such series to
be redeemed or (ii) to register the transfer of or exchange of any Security so
selected for redemption, in whole or in part, except the unredeemed portion of
any Security being redeemed in part.

Section 3.6    Replacement Securities

          If a mutilated Security is surrendered to the Trustee, together with,
in proper cases, such security or indemnity as may be required by the Company or
the Trustee to save each of them harmless, the Company shall execute and the
Trustee shall authenticate and deliver a replacement Security of the same series
and date of maturity, if the Trustee's requirements are met.

          If there shall be delivered to the Company and the Trustee (i)
evidence to their satisfaction of the destruction, loss or theft of any Security
and (ii) such security or indemnity as may be required by them to save each of
them and any agency of either of them harmless, then, in the absence of notice
to the Company or the Trustee that such Security has been acquired by a bona
fide purchaser, the Company shall execute and the Trustee shall authenticate and
deliver in lieu of any such destroyed, lost or stolen Security, a replacement
Security of the same series and principal amount, containing identical terms and
provisions and bearing a number not contemporaneously outstanding.

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

          Upon the issuance of any new Security under this Section, the Company
may require the payment of a sum sufficient to cover any tax or other
governmental charge that may be imposed in relation thereto and any other
expenses (including the fees and expenses of the Trustee connected therewith).

          Every new Security of any series issued pursuant to this Section in
lieu of any destroyed, lost or stolen Security, shall constitute an original
additional contractual obligation of the Company, whether or not the destroyed,
lost or stolen Security shall be at any time enforceable by anyone, and shall be
entitled to all the benefits of this Indenture equally and proportionately with
any and all other Securities of that series duly issued hereunder.

                                      -24-
<PAGE>

          The provisions of this Section are exclusive and shall preclude (to
the extent lawful) all other rights and remedies with respect to the replacement
or payment of mutilated, destroyed, lost or stolen Securities.

Section 3.7    Payment of Interest; Interest Rights Preserved

          Unless otherwise provided as contemplated by Section 3.1, interest, if
any, on any Security which is payable, and is punctually paid or duly provided
for, on any Interest Payment Date shall be paid to the Person in whose name that
Security (or one or more Predecessor Securities) is registered at the close of
business on the Regular Record Date for such interest at the office or agency
maintained for such purpose pursuant to Section 9.2; provided, however, that, at
                                                     --------  -------
the option of the Company, interest on any series of Securities that bear
interest may be paid (i) by check mailed to the address of the Person entitled
thereto as it shall appear on the Register of Holders of Securities of such
series or (ii) to the extent specified as contemplated by Section 3.1, by wire
transfer to an account maintained by the Person entitled thereto as specified in
the Register of Holders of Securities of such series.

          Unless otherwise provided as contemplated by Section 3.1, any interest
on any Security of any series which is payable, but is not punctually paid or
duly provided for, on any interest payment date (herein called "Defaulted
Interest") shall forthwith cease to be payable to the Holder on the relevant
Regular Record Date by virtue of having been such Holder, and such Defaulted
Interest may be paid by the Company, at its election in each case, as provided
in clause (1) or (2) below:

               (1)  The Company may elect to make payment of any Defaulted
          Interest to the Persons in whose names the Securities of such series
          (or their respective Predecessor Securities) are registered at the
          close of business on a Special Record Date for the payment of such
          Defaulted Interest, which shall be fixed in the following manner. The
          Company shall deposit with the Trustee an amount of money equal to the
          aggregate amount proposed to be paid in respect of such Defaulted
          Interest or shall make arrangements satisfactory to the trustee for
          such deposit prior to the date of the proposed payment, such money
          when deposited to be held in trust for the benefit of the Persons
          entitled to such Defaulted Interest as in this clause (1) provided.
          Thereupon the Trustee shall fix a Special Record Date for the payment
          of such Defaulted Interest which shall be not more than 15 days and
          not less than 10 days prior to the date of the proposed payment and
          not less than 10 days after the receipt by the Trustee of the notice
          of the proposed payment. The Trustee shall promptly notify the Company
          of such Special Record Date and, in the name and at the expense of the
          Company shall cause notice of the proposed payment of such Defaulted
          Interest and the Special Record Date therefor to be mailed, first-
          class postage prepaid, to each Holder of Securities of such series at
          his address as it appears in the Register, not less than 10 days prior
          to such Special Record Date. Notice of the proposed payment of such
          Defaulted Interest and the Special Record Date therefor having been so
          mailed, such Defaulted Interest shall be paid to the Persons in whose
          names the Securities of such series (or their respective Predecessor
          Securities) are registered at the close of business

                                      -25-
<PAGE>

          on such Special Record Date and shall no longer be payable pursuant to
          the following clause (2).

               (2)  The Company may make payment of any Defaulted Interest to
          the Persons in whose names the Securities of such series (or their
          respective Predecessor Securities) are registered at the close of
          business on a specified date in any other lawful manner not
          inconsistent with the requirements of any securities exchange on which
          such Securities may be listed, and upon such notice as may be required
          by such exchange, if, after notice given by the Company to the Trustee
          of the proposed payment pursuant to this clause (2), such manner of
          payment shall be deemed practicable by the Trustee.

          Subject to the foregoing provisions of this Section and Section 3.5,
each Security delivered under this Indenture upon registration of transfer of or
in exchange for or in lieu of any other Security shall carry the rights to
interest accrued and unpaid, and to accrue, which were carried by such other
Security.

Section 3.8    Persons Deemed Owners

          Prior to due presentment of any Security for registration of transfer,
the Company, the Trustee and any agent of the Company or the Trustee may treat
the Person in whose name such Security is registered as the owner of such
Security for the purpose of receiving payment of principal of, premium, if any,
and (subject to Section 3.7) interest on such Security and for all other
purposes whatsoever, whether or not such Security be overdue, and neither the
Company, the Trustee nor any agent of the Company or the Trustee shall be
affected by notice to the contrary.

Section 3.9    Cancellation

          The Company at any time may deliver Securities to the Trustee for
cancellation. The Registrar and any Paying Agent shall forward to the Trustee
any Securities surrendered to them for replacement, for registration of
transfer, or for exchange or payment. The Trustee shall cancel all Securities
surrendered for replacement, for registration of transfer, or for exchange,
payment, redemption or cancellation and may dispose of cancelled Securities and
issue a certificate of destruction to the Company. The Company may not issue new
Securities to replace Securities that it has paid or delivered to the Trustee
for cancellation, except as expressly permitted in the terms of Securities for
any particular series or as permitted pursuant to the terms of this Indenture.

Section 3.10   Computation of Interest

          Except as otherwise specified as contemplated by Section 3.1 (i)
interest of any Securities that bear interest at a fixed rate shall be computed
on the basis of a 360-day year of twelve 30 day months and (ii) interest on any
Securities the bear interest at a variable rate shall be computed on the basis
of the actual number of days in an interest period divided by 360 or the actual
number of days in the year.

                                      -26-
<PAGE>

Section 3.11   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
addition to the other identification numbers printed on the Securities) 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.

                                   ARTICLE 4

                    Satisfaction, Discharge and Defeasance

Section 4.1    Termination of Company's Obligations Under the Indenture

          Except as otherwise provided as contemplated by Section 3.1, this
Indenture shall upon Company Request cease to be of further effect with respect
to Securities of or within any series (except as to any surviving rights of
registration of transfer or exchange of such Securities and replacement of such
Securities which may have been lost, stolen or mutilated as herein expressly
provided for) and the Trustee, at the expense of the Company, shall execute
proper instruments acknowledging satisfaction and discharge of this Indenture
with respect to such Securities when

               (1)  either

                    (A)  all such Securities previously authenticated and
               delivered (other than (i) such Securities which have been
               destroyed, lost or stolen and which have been replaced or paid as
               provided in Section 3.6, and (ii) such Securities for whose
               payment money has theretofore been deposited in trust or
               segregated and held in trust by the Company and thereafter repaid
               to the Company or discharged from such trust, as provided in
               Section 9.3) have been delivered to the Trustee for cancellation;
               or

                    (B)  all Securities of such series not theretofore delivered
               to the Trustee for cancellation

                         (i)    have become due and payable, or

                         (ii)   will become due and payable at their Stated
                    Maturity within one year, or

                         (iii)  if redeemable at the option of the Company, are
                    to be called for redemption within one year under
                    arrangements satisfactory

                                      -27-
<PAGE>

                    to the Trustee for giving of notice of redemption by the
                    Trustee in the name, and at the expense, of the Company,

               and the Company, in the case of (i), (ii) or (iii) above, has
               irrevocably deposited or caused to be deposited with the Trustee
               as trust funds in trust for the purpose an amount sufficient to
               pay and discharge the entire indebtedness on such Securities not
               theretofore delivered to the Trustee for cancellation, for
               principal, premium, if any, and interest, with respect thereto,
               to the date of such deposit (in the case of Securities which have
               become due and payable) or to the Stated Maturity or Redemption
               Date, as the case may be;

               (2)  the Company has paid or caused to be paid all other sums
          payable hereunder by the Company; and

               (3)  the Company has delivered to the Trustee an Officers'
          Certificate and an Opinion of Counsel, each stating that all
          conditions precedent herein provided for relating to the satisfaction
          and discharge of this Indenture as to such series have been complied
          with.

Notwithstanding the satisfaction and discharge of this Indenture, the obligation
of the Company to the Trustee and any predecessor Trustee under Section 6.8, the
obligations of the Company to any Authenticating Agent under Section 6.13 and,
if money shall have been deposited with the Trustee pursuant to subclause (B) of
clause (1) of this Section, the obligations of the Trustee under Section 4.2 and
the last paragraph of Section 9.3 shall survive.

Section 4.2  Application of Trust Funds

          Subject to the provisions of the last paragraph of Section 9.3, all
money deposited with the Trustee pursuant to Section 4.1 shall be held in trust
and applied by it, in accordance with the provisions of the Securities and this
Indenture, to the payment, either directly or through any Paying Agent
(including the Company acting as its own Paying Agent) as the Trustee may
determine, to the Persons entitled thereto, of the principal, premium, if any,
and any interest for whose payment such money has been deposited with or
received by the Trustee, but such money need not be segregated from other funds
except to the extent required by law.

Section 4.3  Applicability of Defeasance Provisions; Company's Option to Effect
          Defeasance or Covenant Defeasance

          If pursuant to Section 3.1 provision is made for either or both of (i)
defeasance of the Securities of or within a series under Section 4.4 or (ii)
covenant defeasance of the Securities of or within a series under Section 4.5,
then the provisions of such Section or Sections, as the case may be, together
with the provisions of Sections 4.6 through 4.9 inclusive, with such
modifications thereto as may be specified pursuant to Section 3.1 with respect
to any Securities, shall be applicable to such Securities, and the Company may
at its option by Board Resolution, at any time, with respect to such Securities,
elect to have Section 4.4 (if

                                      -28-
<PAGE>

applicable) or Section 4.5 (if applicable) be applied to such Outstanding
Securities upon compliance with the conditions set forth below in this Article.

Section 4.4  Defeasance and Discharge

          Upon the Company's exercise of the option specified in Section 4.3
applicable to this Section with respect to the Securities  of or within a
series, the Company shall be deemed to have been discharged from its obligations
with respect to such Securities on the date the conditions set forth in Section
4.6 are satisfied (hereinafter "defeasance").  For this purpose, such defeasance
means that the Company shall be deemed to have paid and discharged the entire
indebtedness represented by such Securities which shall thereafter be deemed to
be "Outstanding" only for the purposes of Section 4.7 and the other Sections of
this Indenture referred to in clause (ii) of this Section, and to have satisfied
all its other obligations under such Securities and this Indenture insofar as
such Securities are concerned (and the Trustee, at the expense of the Company,
shall on Company Order execute proper instruments acknowledging the same),
except the following which shall survive until otherwise terminated or
discharged hereunder:  (i) the rights of Holders of such Securities to receive,
solely from the trust funds described in Section 4.6(a) and as more fully set
forth in such Section, payments in respect of the principal of, premium, if any,
and interest, if any, on such Securities when such payments are due; (ii) the
Company's obligations with respect to such Securities under Sections 3.5, 3.6,
9.2 and 9.3 and with respect to the payment of additional amounts, if any,
payable with respect to such Securities as specified pursuant to Section
3.1(b)(16); (iii) the rights, powers, trusts, duties and immunities of the
Trustee hereunder; and (iv) this Article 4.  Subject to compliance with this
Article 4, the Company may exercise its option under this Section
notwithstanding the prior exercise of its option under Section 4.5 with respect
to such Securities.  Following a defeasance, payment of such Securities may not
be accelerated because of an Event of Default.

Section 4.5  Covenant Defeasance

          Upon the Company's exercise of the option specified in Section 4.3
applicable to this Section with respect to any Securities of or within a series,
the Company shall be released from its obligations under Sections 7.1, 9.4 and
9.5, and, if specified pursuant to Section 3.1, its obligations under any other
covenant, with respect to such Securities on and after the date the conditions
set forth in Section 4.6 are satisfied (hereinafter, "covenant defeasance"), and
such Securities shall thereafter be deemed to be not "Outstanding" for the
purposes of any direction, waiver, consent or declaration or Act of Holders (and
the consequences of any thereof) in connection with Sections 7.1, 9.4 and 9.5,
or such other covenant, but shall continue to be deemed "Outstanding" for all
other purposes hereunder.  For this purpose, such covenant defeasance means
that, with respect to such Securities, the Company may omit to comply with and
shall have no liability in respect of any term, condition or limitation set
forth in any such Section or such other covenant, whether directly or
indirectly, by reason of any reference elsewhere herein to any such Section or
such other covenant or by reason of reference in any such Section or such other
covenant to any other provision herein or in any other document and such
omission to comply shall not constitute a Default or an Event of

                                      -29-
<PAGE>

Default under Section 5.1(3) or 5.1(7) or otherwise, as the case may be, but,
except as specified above, the remainder of this Indenture and such Securities
shall be unaffected thereby.

Section 4.6  Conditions to Defeasance or Covenant Defeasance

          The following shall be the conditions to application of Section 4.4 or
Section 4.5 to any Securities of or within a series:

               (a)  The Company shall have deposited or caused to be deposited
          irrevocably with the Trustee (or another trustee satisfying the
          requirements of Section 6.11 who shall agree to comply with, and shall
          be entitled to the benefits of, the provisions of Sections 4.3 through
          4.9 inclusive and the last paragraph of Section 9.3 applicable to the
          Trustee, for purposes of such Sections also a "Trustee") as trust
          funds in trust for the purpose of making the payments referred to in
          clauses (x) and (y) of this Section 4.6(a), specifically pledged as
          security for, and dedicated solely to, the benefit of the Holders of
          such Securities, with instructions to the Trustee as to the
          application thereof, (A) money in an amount, or (B) if Securities of
          such series are not subject to repayment at the option of Holders,
          Government Obligations which through the payment of interest and
          principal in respect thereof in accordance with their terms will
          provide, not later than one day before the due date of any payment
          referred to in clause (x) or (y) of this Section 4.6(a), money in an
          amount or (C) a combination thereof in an amount, sufficient, in the
          opinion of a nationally recognized firm of independent certified
          public accountants expressed in a written certification thereof
          delivered to the Trustee, to pay and discharge, and which shall be
          applied by the Trustee to pay and discharge, (x) the principal of,
          premium, if any, and interest, if any, on such Securities on the
          Maturity of such principal or installment of principal or interest and
          (y) any mandatory sinking fund payments applicable to such Securities
          on the day on which such payments are due and payable in accordance
          with the terms of this Indenture and such Securities. Before such a
          deposit the Company may make arrangements satisfactory to the Trustee
          for the redemption of Securities at a future date or dates in
          accordance with Article 10 which shall be given effect in applying the
          foregoing.

               (b)  Such defeasance or covenant defeasance shall not result in a
          breach or violation of, or constitute a Default or Event of Default
          under, this Indenture or result in a breach or violation of, or
          constitute a default under, any other material agreement or instrument
          to which the Company is a party or by which it is bound.

               (c)  No Default or Event of Default under Section 5.1(5) or
          5.1(6) with respect to such Securities shall have occurred and be
          continuing during the period commencing on the date of such deposit
          and ending on the 91st day after such date (it being understood that
          this condition shall not be deemed satisfied until the expiration of
          such period).

                                      -30-
<PAGE>

          (d)  In the case of an election under Section 4.4, the Company shall
     have delivered to the Trustee an Officers' Certificate and an Opinion of
     Counsel to the effect that (i) the Company has received from, or there has
     been published by, the Internal Revenue Service a ruling, or (ii) since the
     date of execution of this Indenture, there has been a change in the
     applicable Federal income tax law, in either case to the effect that, and
     based thereon such opinion shall confirm that, the Holders of such
     Securities will not recognize income, gain or loss for Federal income tax
     purposes as a result of such defeasance and will be subject to Federal
     income tax on the same amount and in the same manner and at the same times,
     as would have been the case if such deposit, defeasance and discharge had
     not occurred.

          (e)  In the case of an election under Section 4.5, the Company shall
     have delivered to the Trustee an Opinion of Counsel to the effect that the
     Holders of such Securities will not recognize income, gain or loss for
     Federal income tax purposes as a result of such covenant defeasance and
     will be subject to Federal income tax on the same amounts, in the same
     manner and at the same times as would have been the case if such covenant
     defeasance had not occurred.

          (f)  The Company shall have delivered to the Trustee an Officers'
     Certificate and an Opinion of Counsel, each stating that all conditions
     precedent to the defeasance under Section 4.4 or the covenant defeasance
     under Section 4.5 (as the case may be) have been complied with and an
     Opinion of Counsel to the effect that either (i) as a result of a deposit
     pursuant to subsection (a) above and the related exercise of the Company's
     option under Section 4.4 or Section 4.5 (as the case may be), registration
     is not required under the Investment Company Act of 1940, as amended, by
     the Company, with respect to the trust funds representing such deposit or
     by the trustee for such trust funds or (ii) all necessary registrations
     under said act have been effected.

          (g)  Such defeasance or covenant defeasance shall be effected in
     compliance with any additional or substitute terms, conditions or
     limitations which may be imposed on the Company in connection therewith as
     contemplated by Section 3.1.

Section 4.7  Deposited Money and Government Obligations to Be Held in Trust

     Subject to the provisions of the last paragraph of Section 9.3, all money
and Government Obligations (or other property as may be provided pursuant to
Section 3.1) (including the proceeds thereof) deposited with the Trustee
pursuant to Section 4.6 in respect of any Securities of any series shall be held
in trust and applied by the Trustee, in accordance with the provisions of such
Securities and this Indenture, to the payment, either directly or through any
Paying Agent (including the Company acting as its own Paying Agent) as the
Trustee may determine, to the Holders of such Securities of all sums due and to
become due thereon in respect of principal, premium, if any, and interest, if
any, but such money need not be segregated from other funds except to the extent
required by law.

                                      -31-
<PAGE>

Section 4.8  Transfers and Distribution at Company Request

     To the extent permitted by the Financial Accounting Standards Board
Statement of Financial Accounting Standards No. 76, as amended or interpreted by
the Financial Accounting Standards Board from time to time, or any successor
thereto ("Standard No. 76"), or to the extent permitted by the Commission, the
Trustee shall, from time to time, take one or more of the following actions as
specified in a Company Request:

          (a)  Retransfer, reassign and deliver to the Company any securities
     deposited with the Trustee pursuant to Section 4.6(a), provided that the
     Company shall in substitution therefor, simultaneously transfer, assign and
     deliver to the Trustee other Government Obligations appropriate to satisfy
     the Company's obligations in respect of the relevant Securities; and

          (b)  The Trustee (and any Paying Agent) shall promptly pay to the
     Company upon Company Request any excess money or securities held by them at
     any time, including, without limitation, any assets deposited with the
     Trustee pursuant to Section 4.6(a) exceeding those necessary for the
     purposes of Section 4.6(a).

     The Trustee shall not take the actions described in subsections (a) and (b)
of this Section 4.8 unless it shall have first received a written report of
Arthur Andersen & Co., or another nationally recognized independent public
accounting firm, (i) expressing their opinion that the contemplated action is
permitted by Standard No. 76 or the Commission, for transactions accounted for
as extinguishment of debt under the circumstances described in paragraph 3.c of
Standard No. 76 or any successor provision and (ii) verifying the accuracy,
after giving effect to such action or actions, of the computations which
demonstrate that the amounts remaining to be earned on the Government
Obligations deposited with the Trustee pursuant to Section 4.6(a) will be
sufficient for purposes of Section 4.6(a).

                                   ARTICLE 5

                             Defaults and Remedies

Section 5.1  Events of Default

     An "Event of Default" occurs with respect to the Securities of any series
if (whatever the reason for such Event of Default and whether it shall be
voluntary or involuntary or be effected by operation of law or pursuant to any
judgment, decree or order of any court or any order, rule or regulation of any
administrative or governmental body):

          (1)  the Company defaults in the payment of interest on any Security
     of that series or any additional amount payable with respect to any
     Security of that series as specified pursuant to Section 3.1(b)(14) when
     the same becomes due and payable and such default continues for a period of
     90 days;

                                      -32-
<PAGE>

          (2)  the Company defaults in the payment of the principal of or any
     premium on any Security of that series when the same becomes due and
     payable at its Maturity or on redemption or otherwise, or in the payment of
     a mandatory sinking fund payment when and as due by the terms of the
     Securities of that series, and in each case such default continues for a
     period of ten days;

          (3)  the Company defaults in the performance of, or breaches, any
     covenant or warranty of the Company in this Indenture with respect to any
     Security of that series (other than a covenant or warranty a default in
     whose performance or whose breach is elsewhere in this Section specifically
     dealt with), and such default or breach continues for a period of 60 days
     after there has been given, by registered or certified mail, to the Company
     by the Trustee or to the Company and the Trustee by the Holders of at least
     25% in principal amount of the Outstanding Securities of that series, a
     written notice specifying such default or breach and requiring it to be
     remedied and stating that such notice is a "Notice of Default" hereunder;

          (4)  the Company defaults under the terms of any agreement or
     instrument evidencing or under which the Company has at the date of this
     Indenture or hereafter outstanding any indebtedness for borrowed money and
     such indebtedness shall be accelerated so that the same shall be or become
     due and payable prior to the date on which the same would otherwise become
     due and payable and the aggregate principal amount thereof so accelerated
     exceeds $50 million and such acceleration is not rescinded or annulled
     within ten days after there has been given, by registered or certified
     mail, to the Company by the Trustee or to the Company and the Trustee by
     the Holders of at least 25% in aggregate principal amount of the
     Outstanding Securities of that series a written notice specifying such
     default and stating that such notice is a "Notice of Default" hereunder;
     (it being understood, however, that, subject to the provisions of Section
     6.1, the Trustee shall not be deemed to have knowledge of such default
     under such agreement or instrument unless either (A) a Responsible Officer
     of the Trustee shall have actual knowledge of such default or (B) a
     Responsible Officer of the Trustee shall have received written notice
     thereof from the Company, from any Holder, from the holder of any such
     indebtedness or from the trustee under any such agreement or other
     instrument); provided, however, that if such default under such agreement
                  --------  -------
     or instrument is remedied or cured by the Company or waived by the holders
     of such indebtedness, then the Event of Default hereunder by reason thereof
     shall be deemed likewise to have been thereupon remedied, cured or waived
     without further action upon the part of either the Trustee or any of such
     Holders;

          (5)  the Company pursuant to or within the meaning of any Bankruptcy
     Law (A) commences a voluntary case, (B) consents to the entry of an order
     for relief against it in an involuntary case, (C) consents to the
     appointment of a Custodian of it or for all or substantially all of its
     property, or (D) makes a general assignment for the benefit of its
     creditors;

                                      -33-
<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, or (C) orders the liquidation of the
     Company; and the order or decree remains unstayed and in effect for 90
     consecutive days; or

          (7)  any other Event of Default provided as contemplated by Section
     3.1 with respect to Securities of that series.

          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.

Section 5.2  Acceleration, Rescission and Annulment

     If an Event of Default with respect to the Securities of any series at the
time Outstanding occurs and is continuing, the Trustee or the Holders of at
least 25% in aggregate principal amount of all of the outstanding Securities of
that series, by written notice to the Company (and, if given by the Holders, to
the Trustee), may declare the principal (or, if the Securities of that series
are Original Issue Discount Securities or Indexed Securities, such portion of
the principal amount as may be specified in the terms of that series) of all the
Securities of that series to be due and payable and upon any such declaration
such principal (or, in the case of original Issue Discount Securities or Indexed
Securities, such specified amount) shall be immediately due and payable.

     At any time after such a declaration of acceleration with respect to
Securities of any series has been made and before a judgment or decree for
payment of the money due has been obtained by the Trustee as hereinafter in this
Article provided, the Holders of a majority in aggregate principal amount of the
outstanding Securities of that series, by written notice to the Trustee, may
rescind and annul such declaration and its consequences if all existing Defaults
and Events of Default with respect to Securities of that series, other than the
nonpayment of the principal of Securities of that series which have become due
solely by such declaration of acceleration, have been cured or waived as
provided in Section 5.7. No such rescission shall affect any subsequent default
or impair any right consequent thereon.

Section 5.3  Collection of Indebtedness and Suits for Enforcement by Trustee

     The Company covenants that if

          (1)  default is made in the payment of any interest on any Security
     when such interest becomes due and payable and such default continues for a
     period of 90 days, or

          (2)  default is made in the payment of the principal of (or premium,
     if any, on) any Security at the Maturity thereof and such default continues
     for a period of 10 days,

                                      -34-
<PAGE>

the Company will, upon demand of the Trustee, pay to it, for the benefit of the
Holders of such Securities, the whole amount then due and payable on such
Securities for principal, premium, if any, and interest and, to the extent that
payment of such interest shall be legally enforceable, interest on any overdue
principal, premium, if any, and on any overdue interest, at the rate or rates
prescribed therefor in such Securities, and, in addition thereto, such further
amount as shall be sufficient to cover the costs and expenses of collection,
including the reasonable compensation, expenses, disbursements and advances of
the Trustee, its agents and counsel.

     If an Event of Default with respect to Securities of any series occurs and
is continuing, the Trustee may in its discretion proceed to protect and enforce
its rights and the rights of the Holders of Securities of such series by such
appropriate judicial proceedings as the Trustee shall deem most effectual to
protect and enforce any such rights, whether for the specific enforcement of any
covenant or agreement in this Indenture or in aid of the exercise of any power
granted herein, or to enforce any other proper remedy.

Section 5.4  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
Holders of Securities allowed in any judicial proceedings relating to the
Company, its creditors or its property.

Section 5.5  Trustee May Enforce Claims Without Possession of Securities

     All rights of action and claims under this Indenture or the Securities may
be prosecuted and enforced by the Trustee without the possession of any of the
Securities or the production thereof in any proceeding relating thereto.

Section 5.6  Delay or Omission Not Waiver

     No delay or omission by the Trustee or any Holder of any Securities to
exercise any right or remedy accruing upon an Event of Default shall impair any
such right or remedy or constitute a waiver of or acquiescence in any such Event
of Default.

Section 5.7  Waiver of Past Defaults

     The Holders of a majority in aggregate principal amount of Outstanding
Securities of any series by notice to the Trustee may waive on behalf of the
Holders of all Securities of such series a past Default or Event of Default with
respect to that series and its consequences except (i) a Default or Event of
Default in the payment of the principal of, premium, if any, or interest on any
Security of such series or (ii) in respect of a covenant or provision hereof
which pursuant to Section 8.2 cannot be amended or modified without the consent
of the Holder of each outstanding Security of such series adversely affected.
Upon any such waiver, such Default shall cease to exist, and any Event of
Default arising therefrom shall be deemed to have been cured, for every purpose
of this Indenture.

                                      -35-
<PAGE>

Section 5.8  Control by Majority

     The Holders of a majority in aggregate principal amount of the Outstanding
Securities of each series affected (with each such series voting as a class)
shall have the right to 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 with respect to Securities of that series; provided,
                                                                 --------
however, that (i) the Trustee may refuse to follow any direction that conflicts
-------
with law or this Indenture, (ii) the Trustee may refuse to follow any direction
that is unduly prejudicial to the rights of the Holders of Securities of such
series not consenting, or that would in the good-faith judgment of the Trustee
have a substantial likelihood of involving the Trustee in personal liability and
(iii) the Trustee may take any other action deemed proper by the Trustee which
is not inconsistent with such direction.

Section 5.9  Limitation on Suits by Holders

     No Holder of any Security of any series shall have any right to institute
any proceeding, judicial or otherwise, with respect to this Indenture, or for
the appointment of a receiver or trustee, or for any other remedy hereunder,
unless:

          (1)  the Holder has previously given written notice to the Trustee of
     a continuing Event of Default with respect to the Securities of that
     series;

          (2)  the Holders of at least 25% in aggregate principal amount of the
     Outstanding Securities of that series have made a written request to the
     Trustee to institute proceedings in respect of such Event of Default in its
     own name as Trustee hereunder;

          (3)  such Holder or Holders have offered 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 for 60 days after its receipt of such notice, request
     and the offer of indemnity has failed to institute any such proceedings;
     and

          (5)  during such 60-day period, the Holders of a majority in aggregate
     principal amount of the Outstanding Securities of that series has not given
     to the Trustee a direction inconsistent with such written request.

     No one or more Holders shall have any right in any manner whatever by
virtue of, or by availing of, any provision of this Indenture to affect, disturb
or prejudice the rights of any other of such Holders, or to obtain or to seek to
obtain priority or preference over any other of such Holders or to enforce any
right under this Indenture, except in the manner herein provided and for the
equal and ratable benefit of all of such Holders.

                                      -36-
<PAGE>

Section 5.10  Rights of Holders to Receive Payment

     Notwithstanding any other provision of this Indenture, the right of any
Holder of a Security to receive payment of principal of, premium, if any, and,
subject to Section 3.7, interest on the Security, on or after the respective due
dates expressed in the Security (or, in case of redemption, on the redemption
dates), or, subject to Section 5.9, to bring suit for the enforcement of any
such payment on or after such respective dates, shall not be impaired or
affected without the consent of such Holder.

Section 5.11  Application of Money Collected

     If the Trustee collects any money pursuant to this Article, it shall pay
out the money in the following order, at the date or dates fixed by the Trustee
and, in case of the distribution of such money on account of principal, premium,
if any, or interest, upon presentation of the Securities and the notation
thereon of the payment if only partially paid and upon surrender thereof if
fully paid:

          First: to the Trustee for amounts due under Section 6.9;
          -----

          Second: to Holders of Securities in respect of which or for the
          ------
     benefit of which such money has been collected for amounts due and unpaid
     on such Securities for principal of, premium, if any, and interest,
     ratably, without preference or priority of any kind, according to the
     amounts due and payable on such Securities for principal, premium, if any,
     and interest, respectively; and

          Third: to the Company.
          -----

Section 5.12  Restoration of Rights and Remedies

     If the Trustee or any Holder has instituted any proceeding to enforce any
right or remedy under this Indenture and such proceeding has been discontinued
or abandoned for any reason, or has been determined adversely to the Trustee or
to such Holder, then and in every such case, subject to any determination in
such proceeding, the Company, the Trustee and the Holders shall be restored
severally and respectively to their former positions hereunder and thereafter
all rights and remedies of the Trustee and the Holders shall continue as though
no such proceeding had been instituted.

Section 5.13  Rights and Remedies Cumulative

     Except as otherwise provided with respect to the replacement or payment of
mutilated, destroyed, lost or stolen Securities in the last paragraph of Section
3.6, no right or remedy herein conferred upon or reserved to the Trustee or the
Holders is intended to be exclusive of any other right or remedy, and every
right and remedy shall, to the extent permitted by law, be cumulative and in
addition to every other right and remedy given hereunder or now or hereafter
existing at law or in equity or otherwise.  The assertion or employment of any
right

                                      -37-
<PAGE>

or remedy hereunder, or otherwise, shall not prevent the concurrent assertion or
employment of any other appropriate right or remedy.

                                   ARTICLE 6

                                  The Trustee

Section 6.1  Certain Duties and Responsibilities

     (a)  Except during the continuance of an Event of Default,

          (1)  the Trustee undertakes to perform such duties and only such
     duties as are specifically set forth in this Indenture, and no implied
     covenants or obligations shall be read into this Indenture against the
     Trustee; and

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

     (b)  In case an Event of Default has occurred and is continuing with
respect to the Securities of any series, the Trustee shall exercise such of the
rights and powers vested in it by this Indenture with respect to the Securities
of such series, 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.

     (c)  No provision of this Indenture shall be construed to relieve the
Trustee from liability for its own negligent action, its own negligent failure
to act, or its own willful misconduct, except that:
                                       ------

          (1)  this subjection shall not be construed to limit the effect of
     subsection (a) of this Section;

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

          (3)  the Trustee shall not be liable with respect to any action taken
     or omitted to be taken by it in good faith in accordance with the direction
     of the Holders of a majority in principal amount of the Outstanding
     Securities of any series relating to the time, method and place of
     conducting any proceeding for any remedy available to the Trustee, or
     exercising any trust or power conferred upon the Trustee, under this
     Indenture with respect to the Securities of such series.

                                      -38-
<PAGE>

     (d)  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.

     (e)  Whether or not therein expressly so provided, every provision of this
Indenture relating to the conduct or affecting the liability of or affording
protection to the Trustee shall be subject to the provisions of this Section.

Section 6.2  Rights of Trustee

     Subject to the provisions of the Trust Indenture Act:

          (a)  The Trustee may rely and shall be protected in acting or
     refraining from acting upon any resolution, certificate, statement,
     instrument, opinion, report, notice, request, direction, consent, order,
     bond, debenture, note or other paper or document believed by it to be
     genuine and to have been signed or presented by the proper party or
     parties.

          (b)  Any request or direction of the Company mentioned herein shall be
     sufficiently evidenced by a Company Request or Company Order (other than
     delivery of any Security to the Trustee for authentication and delivery
     pursuant to Section 3.3, which shall be sufficiently evidenced as provided
     therein) and any resolution of the Board of Directors may be sufficiently
     evidenced by a Board Resolution.

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

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

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

          (f)  The Trustee shall not be bound to make any investigation into the
     facts or matters stated in any resolution, certificate, statement,
     instrument, opinion, report, notice, request, direction, consent, order,
     bond, debenture, note or other paper or

                                      -39-
<PAGE>

     document, but the Trustee, in its discretion, may make such further inquiry
     or investigation into such facts or matters as it may see fit, and, if the
     Trustee shall determine to make such further inquiry or investigation, it
     shall be entitled to examine the books, records and premises of the
     Company, personally or by agent or attorney.

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

          (h)  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.

          (i)  The Trustee shall not be required 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 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.

Section 6.3  Trustee May Hold Securities

     The Trustee, any Paying Agent, any Registrar or any other agent of the
Company, in its individual or any other capacity, may become the owner or
pledgee of Securities and, subject to Sections 310(b) and 311 of the Trust
Indenture Act, may otherwise deal with the Company, an Affiliate or Subsidiary
with the same rights it would have if it were not Trustee, Paying Agent,
Registrar or such other agent.

Section 6.4  Money Held in Trust

     Money held by the Trustee in trust hereunder need not be segregated from
other funds except to the extent required by law.  The Trustee shall be under no
liability for interest on any money received by it hereunder except as otherwise
agreed with the Company.

Section 6.5  Trustee's Disclaimer

     The recitals contained herein and in the Securities, except the Trustee's
certificate of authentication, shall be taken as the statements of the Company,
and the Trustee assumes no responsibility for their correctness.  The Trustee
makes no representation as to the validity or adequacy of this Indenture or the
Securities.  The Trustee shall not be accountable for the Company's use of the
proceeds from the Securities or for monies paid over to the Company pursuant to
the Indenture.

Section 6.6  Notice of Defaults

     If a Default occurs and is continuing with respect to the Securities of any
series and if it is known to the Trustee, the Trustee shall, within 90 days
after it occurs, transmit, in the manner and to the extent provided in Section
313(c) of the Trust Indenture Act, notice of all

                                      -40-
<PAGE>

uncured Defaults known to it; provided, however, that, except in the case of a
                              --------  -------
Default in payment on the Securities of any series, the Trustee may withhold the
notice if and so long as the board of directors, the executive committee or a
committee of its Responsible Officers in good faith determines that withholding
such notice is in the interests of Holders of Securities of that series;
provided further that, in the case of any default or breach of the character
-------- -------
specified in Section 5.1(3) with respect to the Securities of such series, no
such notice to Holders shall be given until at least 60 days after the
occurrence thereof.

Section 6.7  Reports by Trustee to Holders

     Within 60 days after each May 15 of each year commencing with the first May
15 after the first issuance of Securities pursuant to this Indenture, the
Trustee shall transmit by mail to all Holders of Securities as provided in
Section 313(c) of the Trust Indenture Act a brief report dated as of such May 15
if required by Section 313(a) of the Trust Indenture Act.  The Trustee also
shall comply with Section 313(b) and (d) of the Trust Indenture Act.

Section 6.8  Securityholder Lists

     The Trustee shall preserve in as current a form as is reasonably
practicable the most recent list available to it of the names and addresses of
Holders of Securities of each series. If the Trustee is not the Registrar, the
Company shall furnish to the Trustee semiannually on or before the last day of
June and December in each year, 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, containing all the information in the possession of the
Registrar, the Company or any of its Paying Agents other than the Trustee as to
the names and addresses of Holders of Securities of each such series.

Section 6.9  Compensation and Indemnity

     (a) The Company shall pay to the Trustee from time to time such
compensation as shall be agreed between the Company and the Trustee for all
services rendered by it hereunder.  The Trustee's compensation shall not be
limited by any law on compensation of a trustee of an express trust.  The
Company shall reimburse the Trustee upon request for all reasonable out-of-
pocket expenses incurred by it in connection with the performance of its duties
under this Indenture, except any such expense as may be attributable to its
negligence or bad faith.  Such expenses shall include the reasonable
compensation and expenses of the Trustee's agents and counsel.

     (b) The Company shall indemnify the Trustee for, and hold it harmless
against, any loss, liability or expense incurred by it without negligence or bad
faith on its part arising out of or in connection with its acceptance or
administration of the trust or trusts hereunder.  The Trustee shall notify the
Company promptly of any claim for which it may seek indemnity.  The Company
shall defend the claim and the Trustee shall cooperate in the defense.  The
Trustee may have separate counsel and the Company shall pay the reasonable fees
and

                                      -41-
<PAGE>

expenses of such counsel.  The Company need not pay for any settlement made
without its consent.

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

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

     (e) when the Trustee incurs expenses or renders services in connection with
an Event of Default specified in Section 5.1(5) or Section 5.1(6), the expenses
(including the reasonable charges and expenses of its counsel) and the
compensation for the services are intended to constitute expenses of
administration under any applicable Federal or state bankruptcy, insolvency or
other similar law.

     (f) The provisions of this Section shall survive the termination of this
Indenture.

Section 6.10  Replacement of Trustee

     (a) The resignation or removal of the Trustee and the appointment of a
successor Trustee shall become effective only upon the successor Trustee's
acceptance of appointment as provided in Section 6.11.

     (b) The Trustee may resign at any time with respect to the Securities of
any series by giving written notice thereof to the Company.  If the instrument
of acceptance by a successor Trustee required by Section 6.11 shall not have
been delivered to the Trustee within 30 days after the giving of such notice of
resignation, the resigning Trustee may petition any court of competent
jurisdiction for the appointment of a successor Trustee with respect to the
Securities or such series.

     (c) The Holders of a majority in aggregate principal amount of the
Outstanding Securities of any series may remove the Trustee with respect to that
series by so notifying the Trustee and the Company and may appoint a successor
Trustee for such series with the Company's consent.

     (d)  If at any time:

          (1) the Trustee fails to comply with Section 310(b) of the Trust
     Indenture Act after written request therefor by the Company or by any
     Holder who has been a bona fide Holder of a Security for at least six
     months; or

          (2) the Trustee shall cease to be eligible under Section 310(a) of the
     Trust Indenture Act and shall fail to resign after written request therefor
     by the Company or

                                      -42-
<PAGE>

     by any Holder of a Security who has been a bona fide Holder of a Security
     for at least six months; or

          (3) the Trustee becomes incapable of acting, is adjudged a bankrupt or
     an insolvent or a receiver or public officer takes charge of the Trustee or
     its property or affairs for the purpose of rehabilitation, conservation or
     liquidation, then, in any such case, (i) the Company by or pursuant to a
     Board Resolution may remove the Trustee with respect to all Securities, or
     (ii) subject to Section 315(e) of the Trust Indenture Act, any Holder who
     has been a bona fide Holder of a Security for at least six months may, on
     behalf of himself and all other similarly situated, petition any court of
     competent jurisdiction for the removal of the Trustee with respect to all
     Securities and the appointment of a successor Trustee or Trustees.

     (e) If the Trustee resigns or is removed or if a vacancy exists in the
office of Trustee for any reason, with respect to Securities of one or more
series, the Company, by or pursuant to Board Resolution, shall promptly appoint
a successor Trustee with respect to the Securities of that or those series (it
being understood that any such successor Trustee may be appointed with respect
to the Securities of one or more or all of such series and that at any time
there shall be only one Trustee with respect to the Securities of any particular
series) and shall comply with the applicable requirements of Section 6.11.  If,
within one year after such resignation, removal or incapability, or the
occurrence of such vacancy, a successor Trustee with respect to the Securities
of any series shall be appointed by Act of the Holders of a majority in
principal amount of the Outstanding Securities of such series delivered to the
Company and the retiring Trustee, the successor Trustee so appointed shall,
forthwith upon its acceptance of such appointment in accordance with the
applicable requirements of Section 6.11, become the successor Trustee with
respect to the Securities of such series and to that extent supersede the
successor Trustee appointed by the Company.  If no successor Trustee with
respect to the Securities of any series shall have been so appointed by the
Company or the Holders and accepted appointment in the manner required by
Section 6.11, any Holder who has been a bona fide Holder of a Security of such
series for at least six months may, on behalf of himself and all others
similarly situated, petition any court of competent jurisdiction for the
appointment of a successor Trustee with respect to the Securities of such
series.

Section 6.11  Acceptance of Appointment by Successor

     (a) In case of the appointment hereunder of a successor Trustee with
respect to all Securities, every such successor Trustee shall execute,
acknowledge and deliver to the Company and to the retiring Trustee an instrument
accepting such appointment.  Thereupon, the resignation or removal of the
retiring Trustee shall become effective, and the successor Trustee, without
further act, deed or conveyance, shall become vested with all the rights, powers
and duties of the retiring Trustee; but, on the request of the Company or the
successor Trustee, such retiring Trustee shall, upon payment of its charges,
execute and deliver an instrument transferring to such successor Trustee all the
rights, powers and trusts of the

                                      -43-
<PAGE>

retiring Trustee and shall duly assign, transfer and deliver to such successor
Trustee all property and money held by such retiring Trustee hereunder.

     (b) In case of the appointment hereunder of a successor Trustee with
respect to the Securities of one or more (but not all) series, the Company, the
retiring Trustee and such successor Trustee shall execute and deliver an
indenture supplemental hereto wherein such successor Trustee shall accept such
appointment and which (i) shall contain such provisions as shall be necessary or
desirable to transfer and confirm to, and to vest in, such successor Trustee all
the rights, powers, trusts and duties of the retiring Trustee with respect to
the Securities of that or those series to which the appointment of such
successor Trustee relates, (ii) if the retiring Trustee is not retiring with
respect to all Securities, shall contain such provisions as shall be deemed
necessary or desirable to confirm that all the rights, powers, trusts and duties
of the retiring Trustee with respect to the Securities of that or those series
as to which the retiring Trustee is not retiring shall continue to be vested in
the retiring Trustee, and (iii) shall add to or change any of the provisions of
this Indenture as shall be necessary to provide for or facilitate the
administration of the trusts hereunder by more than one Trustee, it being
understood that nothing herein or in such supplemental indenture shall
constitute such Trustees co-trustees of the same trust and that each such
Trustee shall be trustee of a trust or trusts hereunder separate and apart from
any trust or trusts hereunder administered by any other such Trustee and upon
the execution and delivery of such supplemental indenture the resignation or
removal of the retiring Trustee shall become effective to the extent provided
therein and each such successor Trustee, without any further act, deed or
conveyance, shall become vested with all the rights, powers, trusts and duties
of the retiring Trustee with respect to the Securities of that or those series
to which the appointment of such successor Trustee relates; but, on request of
the Company or any successor Trustee, such retiring Trustee shall duly assign,
transfer and deliver to such successor Trustee all property and money held by
such retiring Trustee hereunder with respect to the Securities of that or those
series to which the appointment of such successor Trustee relates.

     (c) Upon request of any such successor Trustee, the Company shall execute
any and all instruments for more fully and certainly vesting in and confirming
to such successor Trustee all such rights, powers and trusts referred to in
paragraph (a) or (b) of this Section, as the case may be.

     (d) No successor Trustee shall accept its appointment unless at the time of
such acceptance such successor Trustee shall be qualified and eligible under the
Trust Indenture Act.

     (e) The Company shall give notice of each resignation and each removal of
the Trustee with respect to the Securities of any series and each appointment of
a successor Trustee with respect to the Securities of any series in the manner
provided for notices to the Holders of Securities in Section 1.6.  Each notice
shall include the name of the successor Trustee with respect to the securities
of such series and the address of its Corporate Trust office.

                                      -44-
<PAGE>

Section 6.12  Eligibility; Disqualification

     There shall at all times be a Trustee hereunder which shall be eligible to
act as Trustee under Section 310(a)(1) of the Trust Indenture Act and shall have
a combined capital and surplus of at least $50 million. If such corporation
publishes reports of condition at least annually, pursuant to law or the
requirements of Federal, State Territorial or District of Columbia supervising
or examining authority, then for the purposes of this Section, the combined
capital and surplus of such corporation shall be deemed to be its combined
capital and surplus as set forth in its most recent report of condition so
published. If at any time the Trustee shall cease to be eligible in accordance
with the provisions of this Section, it shall resign immediately in the manner
and with the effect hereinafter specified in this Article.

Section 6.13  Merger, Conversion, Consolidation or Succession to Business

     Any corporation into which the Trustee may be merged or converted or with
which it may be consolidated, or any corporation resulting from any merger,
conversion or consolidation to which the Trustee shall be a party, or any
corporation succeeding to all or substantially all the corporate trust business
of the Trustee, shall be the successor of the Trustee hereunder, provided such
corporation shall be otherwise qualified and eligible under this Article,
without the execution or filing of any paper or any further act on the part of
any of the parties hereto.  In case any Securities shall have been
authenticated, but not delivered, by the Trustee then in office, any successor
by merger, conversion or consolidation to such authenticating Trustee may adopt
such authentication and deliver the Securities so authenticated with the same
effect as if such successor Trustee had itself authenticated such Securities.

Section 6.14  Appointment of Authenticating Agent

     The Trustee may appoint an Authenticating Agent or Agents with respect to
one or more series of Securities which shall be authorized to act on behalf of
the Trustee to authenticate Securities of such series issued upon original issue
exchange, registration of transfer or partial redemption thereof, and Securities
so authenticated shall be entitled to the benefits of this Indenture and shall
be valid and obligatory for all purposes as if authenticated by the Trustee
hereunder.  Any such appointment shall be evidenced by an instrument in writing
signed by a Responsible Officer of the Trustee, a copy of which instrument shall
be promptly furnished to the Company.  Wherever reference is made in this
Indenture to the authenticating and delivery of Securities by the Trustee or the
Trustee's certificate of authentication, such reference shall be deemed to
include authentication and delivery on behalf of the Trustee by an
Authenticating Agent and a certificate of authentication executed on behalf of
the Trustee by an Authenticating Agent.  Each Authenticating Agent shall be
acceptable to the Company and, except as may otherwise be provided pursuant to
Section 3.1, shall at all times be a bank or trust company or corporation
organized and doing business and in good standing under the laws of the United
States of America or of any State or the District of Columbia, authorized under
such laws to act as Authenticating Agent, having a combined capital and surplus
of not less than $10 million and subject to supervision or examination by

                                      -45-
<PAGE>

Federal or State authorities. If such Authenticating Agent publishes reports of
condition at least annually, pursuant to law or the requirements of the
aforesaid supervising or examining authority, then for the purposes of this
Section, the combined capital and surplus of such Authenticating Agent shall be
deemed to be its combined capital and surplus as set forth in its most recent
report of condition so published. In case at any time an Authenticating Agent
shall cease to be eligible in accordance with the provisions of this Section,
such Authenticating Agent shall resign immediately in the manner and with the
effect specified in this Section.

     Any corporation into which an Authenticating Agent may be merged or
converted or with which it may be consolidated, or any corporation resulting
from any merger, conversion or consolidation to which such Authenticating Agent
shall be a party, or any corporation succeeding to the corporate agency or
corporate trust business of an Authenticating Agent, shall continue to be an
Authenticating Agent, provided, such corporation shall be otherwise eligible
                      --------
under this Section, without the execution or filing of any paper or further act
on the part of the Trustee or the Authenticating Agent.

     An Authenticating Agent for any series of Securities may at any time resign
by giving written notice of resignation to the Trustee for such series and to
the Company. The Trustee for any series of Securities may at any time terminate
the agency of an Authenticating Agent by giving written notice of termination to
such Authenticating Agent and to the Company. Upon receiving such a notice of
resignation or upon such a termination, or in case at any time such
Authenticating Agent shall cease to be eligible in accordance with the
provisions of this Section, the Trustee for such series may appoint a successor
Authenticating Agent which shall be acceptable to the Company and shall give
notice of such appointment to all Holders of Securities of the series with
respect to which such Authenticating Agent will serve in the manner set forth in
Section 1.6. Any successor Authenticating Agent upon acceptance of its
appointment hereunder shall become vested with all the rights, powers and duties
of its predecessor hereunder, with like effect as if originally named as an
Authenticating Agent herein. No successor Authenticating Agent shall be
appointed unless eligible under the provisions of this Section.

     The Company agrees to pay to each Authenticating Agent from time to time
reasonable compensation, including reimbursement of its reasonable expenses for
its services under this Section.

     If an appointment with respect to one or more series is made pursuant to
this Section, the Securities of such series may have endorsed thereon, in
addition to or in lieu of the Trustee's certificate of authentication, an
alternate certificate of authentication substantially in the following form:

     This is one of the Securities of a series issued under the within-mentioned
Indenture.

                                      -46-
<PAGE>

                              _________________________________,
                                as Trustee



                              By    _______________________
                                    as Authenticating Agent



                              By    _______________________
                                    Authorized Officer

Section 6.15  Trustee's Application for Instructions From the Company

     Any application by the Trustee for written instructions from the Company
may, at the option of the Trustee, set forth in writing any action proposed to
be taken or omitted by the Trustee under this Indenture and the date on and/or
after which such action shall be taken or such omission shall be effective. The
Trustee shall not be liable for any action taken by, or omission of, the Trustee
in accordance with a proposal included in such application on or after the date
specified in such application (which date shall not be less than fifteen
Business Days after the date any officer of the Company actually receives such
application, unless any such officer shall have consented in writing to any
earlier date) unless prior to taking any such action (or the effective date in
the case of an omission), the Trustee shall have received written instructions
in response to such application specifying the action to be taken or omitted.

                                   ARTICLE 7


                  Consolidation, Merger or Sale by the Company

Section 7.1  Consolidation, Merger or Sale of Assets Permitted

     The Company may merge or consolidate with or into any other corporation or
sell, convey, transfer, lease or otherwise dispose of all or substantially all
of its assets to any person, firm or corporation, if (i) (A) in the case of a
merger or consolidation, the Company is the surviving corporation or (B) in the
case of a merger or consolidation where the Company is not the surviving
corporation and in the case of any such sale, conveyance or other disposition,
the successor or acquiring corporation is a corporation organized and existing
under the laws of the United States or a State thereof and such corporation
expressly assumes by supplemental indenture all of the obligations of the
Company under the Securities and under this Indenture, (ii) immediately
thereafter, giving effect to such merger or consolidation, or such sale,
conveyance, transfer or other disposition, no Default or Event of Default shall
have occurred and be continuing and (iii) the company has delivered to the
Trustee an Officers' Certificate and an Opinion of Counsel each stating that
such merger or consolidation, or such sale, conveyance, transfer or other
disposition, complies with this Article and that all conditions precedent herein
provided for relating to such transaction have been complied with.

                                      -47-
<PAGE>

In the event of the assumption by a successor corporation of the obligations of
the Company as provided in clause (i)(B) of the immediately preceding sentence,
such successor corporation shall succeed to and be substituted for the Company
hereunder and under the Securities and all such obligations of the Company shall
terminate.

                                   ARTICLE 8


                            Supplemental Indentures

Section 8.1  Supplemental Indentures Without Consent of Holders

     Without the consent of any Holders, the Company, when authorized by a Board
Resolution, and the Trustee, at any time and from time to time, may enter into
indentures supplemental hereto, in form reasonably satisfactory to the Trustee,
for any of the following purposes:

          (1) to evidence the succession of another corporation to the Company
     and the assumption by any such successor of the covenants of the Company
     herein and in the Securities; or

          (2) to add to the covenants of the Company for the benefit of the
     Holders of all or any series of Securities (and if such covenants are to be
     for the benefit of less than all series of Securities, stating that such
     covenants are expressly being included solely for the benefit of such
     series) or to surrender any right or power herein conferred upon the
     Company; or

          (3) to add any additional Events of Default with respect to all or any
     series of Securities; or

          (4) to add to or change any of the provisions of this Indenture to
     such extent as shall be necessary to facilitate the issuance of Securities
     in bearer form, registrable or not registrable as to principal, and with or
     without interest coupons, or to facilitate the issuance of Securities in
     global form; or

          (5) to add to, change or eliminate any of the provisions of this
     Indenture, provided that any such addition, change or elimination shall
                --------
     become effective only when there is no Security Outstanding of any series
     created prior to the execution of such supplemental indenture which is
     entitled to the benefit of such provision; or

          (6) to secure the Securities; or

          (7) to establish the form or terms of Securities of any series as
     permitted by Sections 2.1 and 3.2; or

          (8) to evidence and provide for the acceptance of appointment
     hereunder by a successor Trustee with respect to the Securities of one or
     more series and to add

                                      -48-
<PAGE>

     to or change any of the provisions of this Indenture as shall be necessary
     to provide for or facilitate the administration of the trusts hereunder by
     more than one Trustee, pursuant to the requirements of Section 6.10; or

          (9) to correct or supplement any provision herein which may be
     inconsistent with any other provision herein or to make any other
     provisions with respect to matters or questions arising under this
     Indenture, provided such action shall not adversely affect the interests of
                --------
     the Holders of Securities of any series in any material respect, or to cure
     any ambiguity or correct any mistake.

Section 8.2  With Consent of Holders

     With the written consent of the Holders of a majority of the aggregate
principal amount of the Outstanding Securities of each series adversely affected
by such supplemental indenture, the Company and the Trustee may enter into an
indenture or indentures supplemental hereto to add any provisions to or to
change or eliminate any provisions of this Indenture or of any other indenture
supplemental hereto or to modify the rights of the Holders of Securities of each
such series; provided, however, that without the consent of the Holder of each
             --------  -------
Outstanding Security affected thereby, an amendment under this Section may not:

          (1) change the Stated Maturity of the principal of, or any installment
     of principal of or interest on, any Security, or reduce the principal
     amount thereof or the rate of interest thereon or any premium payable upon
     the redemption thereof, or reduce the amount of the principal of an
     Original Issue Discount Security that would be due and payable upon a
     declaration of acceleration of the Maturity thereof pursuant to Section
     5.2, or change the coin or currency in which, any Securities or any premium
     or the interest thereon is payable, or impair the right to institute suit
     for the enforcement of any such payment on or after the Stated Maturity
     thereof (or, in the case of redemption, on or after the Redemption Date);

          (2) reduce the percentage in principal amount of the Outstanding
     Securities of any series, the consent of whose Holders is required for any
     such supplemental indenture, or the consent of whose Holders is required
     for any waiver (of compliance with certain provisions of this Indenture or
     certain defaults hereunder and their consequences) provided for in this
     Indenture;

          (3) change any obligation of the Company to maintain an office or
     agency in the places and for the purposes specified in Section 9.2; or

          (4) make any change in Section 5.7 or this 8.2(a) except to increase
     any percentage or to provide that certain other provisions of this
     Indenture cannot be modified or waived with the consent of the Holders of
     each Outstanding Security affected thereby.

     A supplemental indenture that changes or eliminates any covenant or other
provision of this Indenture, which has expressly been included solely for the
benefit of one or more

                                      -49-
<PAGE>

particular series of Securities, or that modifies the rights of the Holders of
Securities of such series with respect to such covenant or other provision,
shall be deemed not to affect the rights under this Indenture of the Holders of
Securities of any other series.

     It is not necessary under this Section 8.2 for the Holders to consent to
the particular form of any proposed supplemental indenture, but it is sufficient
if they consent to the substance thereof.

Section 8.3  Compliance With Trust Indenture Act

     Every supplemental indenture executed pursuant to this Article shall comply
with the requirements of the Trust Indenture Act as then in effect.

Section 8.4  Execution of Supplemental Indentures

     In executing, or accepting the additional trusts created by, any
supplemental indenture permitted by this Article or the modification thereby of
the trusts created by this Indenture, the Trustee shall be entitled to receive,
and shall be fully protected in relying upon, an Opinion of Counsel stating that
the execution of such supplemental indenture is authorized or permitted by this
Indenture.  The Trustee may, but shall not be obligated to, enter into any such
supplemental indenture which affects the Trustee's own rights, duties or
immunities under this Indenture or otherwise.

Section 8.5  Effect of Supplemental Indentures

     Upon the execution of any supplemental indenture under this article, this
Indenture shall be modified in accordance therewith, and such supplemental
indenture shall form a part of this Indenture for all purposes; and every Holder
of Securities theretofore or thereafter authenticated and delivered hereunder
shall be bound thereby.

Section 8.6  Reference in Securities to Supplemental Indentures

     Securities of any series authenticated and delivered after the execution of
any supplemental indenture pursuant to this Article may, and shall if required
by the Trustee, bear a notation in form approved by the Trustee as to any matter
provided for in such supplemental indenture.  If the Company shall so determine,
new Securities of any series so modified as to conform, in the opinion of the
Trustee and the Company, to any such supplemental indenture may be prepared and
executed by the Company and authenticated and delivered by the Trustee in
exchange for Outstanding Securities.



                                      -50-
<PAGE>

                                   ARTICLE 9


                                   Covenants

Section 9.1  Payment of Principal, Premium, if Any, and Interest

     The Company covenants and agrees for the benefit of the Holders of each
series of Securities that it will duly and punctually pay the principal of,
premium, if any, and interest on the Securities of that series in accordance
with the terms of the Securities of such series and this Indenture. An
installment of principal or interest shall be considered paid on the date it is
due if the Trustee or Paying Agent holds on that date money designated for and
sufficient to pay the installment.

Section 9.2  Maintenance of Office or Agency

     The Company will maintain in each Place of Payment for any series of
Securities an office or agency where Securities of that series may be presented
or surrendered for payment, where Securities of that series may be surrendered
for registration of transfer or exchange and where notices and demands to or
upon the Company in respect of the Securities of that series and this Indenture
may be served. The Company will give prompt written notice to the Trustee of the
location, and any change in the location, of any such office or agency. If at
any time the Company shall fail to maintain any such required office or agency
or shall fail to furnish the Trustee with the address thereof, such
presentations, surrenders, notices and demands may be made or served at the
Corporate Trust Office of the Trustee, and the Company hereby appoints the
Trustee as its agent to receive all such presentations, surrenders, notices and
demands.

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

     Unless otherwise specified as contemplated by Section 3.1, the Trustee
shall initially serve as Paying Agent.

Section 9.3  Money for Securities to Be Held in Trust; Unclaimed Money

     If the Company shall at any time act as its own Paying Agent with respect
to any series of Securities, it will, on or before each due date of the
principal of, premium, if any, or interest on any of the Securities of that
series, segregate and hold in trust for the benefit of the Persons entitled
thereto a sum sufficient to pay the principal, premium, if any, or interest so
becoming

                                      -51-
<PAGE>

due until such sums shall be paid to such persons or otherwise disposed of as
herein provided and will promptly notify the Trustee in writing of its action or
failure so to act.

     The Company will cause each Paying Agent for any series of Securities other
than the Trustee to execute and deliver to the Trustee an instrument in which
such Paying Agent shall agree with the Trustee, subject to the provisions of
this Section, that such Paying Agent will:

          (1) hold all sums held by it for the payment of the principal of,
     premium, if any, or interest on Securities of that series in trust for the
     benefit of the Persons entitled thereto until such sums shall be paid to
     such Persons or otherwise disposed of as herein provided;

          (2) give the Trustee notice of any default by the Company (or any
     other obligor upon the Securities of that series) in the making of any
     payment of principal, premium, if any, or interest on the Securities; and

          (3) at any time during the continuance of any such default, upon the
     written request of the Trustee, forthwith pay to the Trustee all sums so
     held in trust by such Paying Agent.

     The Company may at any time, for the purpose of obtaining the satisfaction
and discharge of this Indenture or for any other purpose, pay, or by Company
Order direct any paying Agent to pay, to the Trustee all sums held in trust by
the Company or such Paying Agent, such sums to be held by the Trustee upon the
same trusts as those upon which such sums were held by the Company or such
Paying Agent; and, upon such payment by any Paying Agent to the Trustee, such
Paying Agent shall be released from all further liability with respect to such
money.

     Any money deposited with the Trustee or any Paying Agent, or then held by
the Company, in trust for the payment of any principal, premium or interest on
any Security of any series and remaining unclaimed for two years after such
principal, premium, if any, or interest has become due and payable shall be paid
to the Company on Company Request, or (if then held by the Company) shall be
discharged from such trust; and the Holder of such Security shall thereafter, as
an unsecured general creditor, look only to the Company for payment thereof, and
all liability of the Trustee or such Paying Agent with respect to such trust
money, and all liability of the Company as trustee thereof, shall thereupon
cease; provided, however, that the Trustee or such Paying Agent, before being
       --------  -------
required to make any such repayment, may at the expense of the Company cause to
be published once, in a newspaper published in the English language, customarily
published on each Business Day and of general circulation in The City of New
York, or cause to be mailed to such Holder, notice that such money remains
unclaimed and that, after a date specified therein, which shall not be less than
30 days from the date of such publication, any unclaimed balance of such money
then remaining will be repaid to the Company.

                                      -52-
<PAGE>

Section 9.4  Corporate Existence

     Subject to Article 7, the Company will at all times do or cause to be done
all things necessary to preserve and keep in full force and effect its corporate
existence and its rights and franchises; provided that nothing in this Section
                                         --------
9.4 shall prevent the abandonment or termination of any right or franchise of
the Company if, in the opinion of the Company, such abandonment or termination
is in the best interests of the Company and does not materially adversely affect
the ability of the Company to operate its business or to fulfill its obligations
hereunder.

Section 9.5     Insurance

     The Company covenants and agrees that it will maintain, and cause each of
its Subsidiaries to maintain, insurance with responsible and reputable insurance
companies or associations or through a program of self-insurance in such amounts
and covering such risks as are consistent with sound business practice for
corporations engaged in the same or a similar business similarly situated.

Section 9.6  Reports by the Company

     The Company covenants:

          (a) to file with the Trustee, within 30 days after the Company is
     required to file the same with the Commission, copies of the annual reports
     and of the information, documents and other reports (or copies of such
     portions of any of the foregoing as the Commission may from time to time by
     rules and regulations prescribe) which the Company may be required to file
     with the Commission pursuant to section 13 or section 15(d) of the
     Securities Exchange Act of 1934, as amended; or, if the Company is not
     required to file information, documents or reports pursuant to either of
     such sections, then to file with the Trustee and the Commission, in
     accordance with rules and regulations prescribed from time to time by the
     Commission, such of the supplementary and periodic information, documents
     and reports which may be required pursuant to section 13 of the Securities
     Exchange Act of 1934, as amended, in respect of a security listed and
     registered on a national securities exchange as may be prescribed from time
     to time in such rules and regulations;

          (b) to file with the Trustee and the Commission, in accordance with
     the rules and regulations prescribed from time to time by the Commission,
     such additional information, documents and reports with respect to
     compliance by the Company with the conditions and covenants provided for in
     this Indenture, as may be required from time to time by such rules and
     regulations; and

          (c) to transmit to all Holders of Securities, within 30 days after the
     filing thereof with the Trustee, in the manner and to the extent provided
     in section 313(c) of the Trust Indenture Act, such summaries of any
     information, documents and reports

                                      -53-
<PAGE>

     required to be filed by the Company pursuant to subsections (a) and (b) of
     this Section 9.6, as may be required by rules and regulations prescribed
     from time to time by the Commission.

Section 9.7  Annual Review Certificate; Notice of Default

     The Company covenants and agrees to 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.  For purposes of this Section
9.7, such compliance shall be determined without regard to any period of grace
or requirement of notice provided under this Indenture.  The Company shall file
with the Trustee written notice of occurrence of any Event of Default within 30
Business Days of its becoming aware of any such Event of Default.

Section 9.8  Provision of Financial Statements

     If the Company is not required to file with the Commission periodic reports
and other information pursuant to section 13(a), 13(c) or 15(d) of the
Securities Exchange Act of 1934, the Company shall furnish without cost to each
Holder and file with the Trustee (i) within 135 days after the end of each
fiscal year, annual reports containing the information required to be contained
in Items 1, 2, 3, 5, 6, 7, 8 and 9 of Form 10-K promulgated under the Securities
Exchange Act of 1934, or substantially the same information required to be
contained in comparable items of any successor form, (ii) within 60 days after
the end of each of the first three fiscal quarters of each fiscal year,
quarterly reports containing the information required to be contained in Form
10-Q promulgated under the Securities Exchange Act of 1934, or substantially the
same information required to be contained in any successor form and (iii)
promptly from the time after the occurrence of an event required to be therein
reported, such other reports containing information required to be contained in
Form 8-K promulgated under the Securities Exchange Act of 1934, or substantially
the same information required to be contained in any successor form.  The
Company shall also make such reports available to prospective purchasers of the
Securities, securities analysts and broker-dealers upon their request.

                                  ARTICLE 10


                                  Redemption

Section 10.1  Applicability of Article

     Securities of any series which are redeemable before their Stated Maturity
shall be redeemable in accordance with their terms and (except as otherwise
specified as contemplated by Section 3.1 for Securities of any series) in
accordance with this Article.

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<PAGE>

Section 10.2  Election to Redeem; Notice to Trustee

     The election of the Company to redeem any Securities shall be evidenced by
or pursuant to a Board Resolution or any Officers' Certificate.  In the case of
any redemption at the election of the Company of less than all the Securities,
if any, of any series, the Company shall, at least 60 days prior to the
Redemption Date fixed by the Company (unless a shorter notice shall be
satisfactory to the Trustee), notify the Trustee of such Redemption Date, of the
principal amount of Securities of such series to be redeemed and, if applicable,
of the tenor of the Securities to be redeemed.  In the case of any redemption of
Securities (i) prior to the expiration of any restriction on such redemption
provided in the terms of such Securities or elsewhere in this Indenture or (ii)
pursuant to an election of the Company which is subject to a condition specified
in the terms of such Securities, the Company shall furnish the Trustee with an
Officers' Certificate evidencing compliance with such restriction or condition.

Section 10.3  Selection of Securities to Be Redeemed

     Unless otherwise specified as contemplated by Section 3.1, if less than all
the Securities of a series with the same original issue date, interest rate and
Stated Maturity are to be redeemed, the Trustee, not more than 45 days prior to
the redemption date, shall select the Securities of the series to be redeemed in
such manner as the Trustee shall deem fair and appropriate.  The Trustee shall
make the selection from Securities of the series that are Outstanding and that
have not previously been called for redemption and may provide for the selection
for redemption of portions (equal to the minimum authorized denomination for
Securities of that series or any integral multiple thereof) of the principal
amount of Securities of such series of a denomination larger than the minimum
authorized denomination for Securities of that series.  The Trustee shall
promptly notify the Company in writing of the Securities selected by the Trustee
for redemption and, in the case of any Securities selected for partial
redemption, the principal amount thereof to be redeemed.

     For purposes of this Indenture, unless the context otherwise requires, all
provisions relating to the redemption of Securities shall relate, in the case of
any Securities redeemed or to be redeemed only in part, to the portion of the
principal amount of such Securities which has been or is to be redeemed.

Section 10.4  Notice of Redemption

     Unless otherwise specified as contemplated by Section 3.1, notice of
redemption shall be given in the manner provided in Section 1.6 not less than 30
days nor more than 60 days prior to the Redemption Date to the Holders of the
Securities to be redeemed.

     All notices of redemption shall state:

          (1)  the Redemption Date;

          (2)  the Redemption Price;

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<PAGE>

          (3) if fewer than all the Outstanding Securities of a series are to be
     redeemed, the identification (and, in the case of partial redemption, the
     principal amounts) of the particular Security or Securities to be redeemed;

          (4) in case any Security is to be redeemed in part only, the notice
     which relates to such Security shall state that on and after the Redemption
     Date, upon surrender of such Security, the holder will receive, without a
     charge, a new Security or Securities of authorized denominations for the
     principal amount thereof remaining unredeemed;

          (5) the Place or Places of Payment where such Securities maturing
     after the Redemption Date, are to be surrendered for payment for the
     Redemption Price;

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

          (7) that, on the Redemption Date, the Redemption Price will become due
     and payable upon each such Security, or the portion thereof, to be redeemed
     and, if applicable, that interest thereon will cease to accrue on and after
     said date;

          (8) that the redemption is for a sinking fund, if such is the case;
     and

          (9)  CUSIP number.

     Notice of redemption of Securities to be redeemed shall be given by the
Company or, at the Company's request, by the Trustee in the name and at the
expense of the Company.

Section 10.5  Deposit of Redemption Price

     On or prior to any Redemption Date, the Company shall deposit with the
Trustee or with a Paying Agent (or, if the Company is acting as its own Paying
Agent, segregate and hold in trust as provided in Section 9.3) an amount of
money sufficient to pay on the Redemption Date the Redemption Price of, and
(unless the Redemption Date shall be an Interest Payment Date) interest accrued
to the Redemption Date on, all Securities or portions thereof which are to be
redeemed on that date.

     Unless any Security by its terms prohibits any sinking fund payment
obligation from being satisfied by delivering and crediting Securities
(including Securities redeemed otherwise than through a sinking fund), the
Company may deliver such Securities to the Trustee for crediting against such
payment obligation in accordance with the terms of such Securities and this
Indenture.

Section 10.6  Securities Payable on Redemption Date

     Notice of redemption having been given as aforesaid, the Securities so to
be redeemed shall, on the Redemption Date, become due and payable at the
Redemption Price therein

                                      -56-
<PAGE>

specified, and from and after such date (unless the Company shall default in the
payment of the Redemption Price and accrued interest) such Securities shall
cease to bear interest. Except as provided in the next succeeding paragraph,
upon surrender of any such Security for redemption in accordance with said
notice, such Security shall be paid by the Company at the Redemption Price,
together with accrued interest to the Redemption Date; provided, however, that,
                                                       --------  -------
unless otherwise specified as contemplated by Section 3.1, installments of
interest on Securities whose Stated Maturity is prior to the Redemption Date
shall be payable to the Holders of such Securities, or one or more Predecessor
Securities, registered as such at the close of business on the relevant Record
Dates according to their terms and the provisions of Section 3.7.

     If any Security called for redemption shall not be so paid upon surrender
thereof for redemption, the principal (and premium, if any) shall, until paid,
bear interest from the Redemption Date at the rate prescribed therefor in the
Security.

Section 10.7  Securities Redeemed in Part

     Upon surrender of a Security that is redeemed in part at any Place of
Payment therefor (with, if the Company or the Trustee so required, 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), the Company shall execute and the Trustee shall
authenticate and deliver to the Holder of that Security, without service charge,
a new Security or Securities of the same series, the same form and the same
Maturity in any authorized denomination equal in aggregate principal amount to
the unredeemed portion of the principal of the Security surrendered.

                                  ARTICLE 11


                                 Sinking Funds

Section 11.1  Applicability of Article

     The provisions of this Article shall be applicable to any sinking fund for
the retirement of Securities of a series except as otherwise specified as
contemplated by Section 3.1 for Securities of such series.

     The minimum amount of any sinking fund payment provided for by the terms of
Securities of any series is herein referred to as a "mandatory sinking fund
payment," and any payment in excess of such minimum amount provided for by the
terms of Securities of any series is herein referred to as an "optional sinking
fund payment."  If provided for by the terms of Securities of any series, the
cash amount of any sinking fund payment may be subject to reduction as provided
in Section 11.2.  Each sinking fund payment shall be applied to the redemption
of Securities of any series as provided for by the terms of Securities of such
series.

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<PAGE>

Section 11.2  Satisfaction of Sinking Fund Payments With Securities

     The Company (i) may deliver Outstanding Securities of a series (other than
any previously called for redemption) and (ii) may apply as a credit Securities
of a series which have been redeemed either at the election of the Company
pursuant to the terms of such Securities or through the application of permitted
optional sinking fund payments pursuant to the terms of such Securities, in each
case in satisfaction of all or any part of any sinking fund payment with respect
to the Securities of such series required to be made pursuant to the terms of
such Securities as provided for by the terms of such series; provided that such
                                                             --------
Securities have not been previously so credited.  Such Securities shall be
received and credited for such purpose by the Trustee at the Redemption Price
specified in such Securities for redemption through operation of the sinking
fund and the amount of such sinking fund payment shall be reduced accordingly.

Section 11.3  Redemption of Securities for Sinking Fund

     Not less than 60 days prior to each sinking fund payment date for any
series of Securities, the Company will deliver to the Trustee an Officers'
Certificate specifying the amount of the next ensuing sinking fund payment for
that series pursuant to the terms of that series, the portion thereof, if any,
which is to be satisfied by payment of cash and the portion thereof, if any,
which is to be satisfied by delivering and crediting Securities of that series
pursuant to Section 11.2 and will also deliver to the Trustee any Securities to
be so delivered.  Not less than 30 days before each such sinking fund payment
date, the Trustee shall select the Securities to be redeemed upon such sinking
fund payment date in the manner specified in Section 10.3 and cause notice of
the redemption thereof to be given in the name of and at the expense of the
Company in the manner provided in Section 10.4.  Such notice having been duly
given, the redemption of such Securities shall be made upon the terms and in the
manner stated in Sections 10.6 and 10.7.

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<PAGE>

     This Indenture may be executed in any number of counterparts, each of which
shall be an original, but such counterparts shall together constitute but one
instrument.

     IN WITNESS WHEREOF, the parties hereto have caused this Indenture to be
duly executed, and their respective corporate seals to be hereunto affixed and
attested, all as of the day and year first above written.


                                   ICOS CORPORATION



                                   By:
                                      ------------------------------------------
                                      Title:  Vice President and Chief Financial
                                   Officer

[Seal]

Attest



_____________________________
Title:  Vice President

                                   ________________________, TRUSTEE


                                   By:__________________________________________
                                      Title:

[Seal]

Attest:




_____________________________
Title:

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