AVIRON
S-3/A, 1998-04-06
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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<PAGE>

     
   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON APRIL 6, 1998      
                                                 REGISTRATION NO. 333-41649     
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                _______________
                                   
                                AMENDMENT NO. 2
                                      TO            
                                    FORM S-3
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933

                                _______________

                                     AVIRON
             (Exact name of Registrant as specified in its charter)

           DELAWARE                                        77-0309686
(State or other jurisdiction of                  (I.R.S. Employer Identification
incorporation or organization)                              Number)

                                _______________

                           297 NORTH BERNARDO AVENUE
                        MOUNTAIN VIEW, CALIFORNIA 94043
                                 (650) 919-6500
         (Address, including zip code, and telephone number, including
            area code, of registrant's principal executive offices)

                                _______________

                             J. LEIGHTON READ, M.D.
                      CHAIRMAN AND CHIEF EXECUTIVE OFFICER
                           297 NORTH BERNANDO AVENUE
                        MOUNTAIN VIEW, CALIFORNIA 94043
                                 (650) 919-6500
 (Name, address, including zip code, and telephone number, including area code,
                             of agent for service)

                                _______________

                                   COPIES TO:

                            ALAN C. MENDELSON, ESQ.
                            ROBERT J. BRIGHAM, ESQ.
                               COOLEY GODWARD LLP
                             FIVE PALO ALTO SQUARE
                              3000 EL CAMINO REAL
                            PALO ALTO, CA 94306-2155
                                 (650) 843-5000

                                _______________

        APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC:
  As soon as practicable after this Registration Statement becomes effective.

                                _______________

  If the only securities being registered on this Form are being offered
pursuant to dividend or interest reinvestment plans, please check the following
box. [ ]

  If any of the securities being registered on this Form are to be offered on a
delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, other than securities offered only in connection with dividend or interest
reinvestment plans, check the following box. [X]

  If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering. [ ]

  If this Form is filed in a post-effective amendment filed pursuant to Rule
462(c) under the Securities Act, check the following box and list the Securities
Act registration statement number of the earlier effective registration
statement of the same offering.  [ ]

  If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. [ ]

                                _______________
                            
                        CALCULATION OF REGISTRATION FEE      
<TABLE>     
<CAPTION> 
=====================================================================================================================
                                                       PROPOSED MAXIMUM       PROPOSED MAXIMUM
  TITLE OF EACH CLASS OF             AMOUNT TO BE          OFFERING              AGGREGATE              AMOUNT OF
SECURITIES TO BE REGISTERED           REGISTERED       PRICE PER SHARE        OFFERING PRICE         REGISTRATION FEE
- ---------------------------------------------------------------------------------------------------------------------
<S>                                  <C>               <C>                     <C>                   <C> 
Common Stock, $0.001 par value        1,714,286           $21.94(1)              $37,611,435(1)         $11,398(1)
                                        600,000            23.31(2)               13,986,000(2)           4,239(2)
=====================================================================================================================
</TABLE>      
    
(1)  Estimated in accordance with Rule 457(c) solely for the purpose of
     computing the amount of the registration fee based on the average of the
     high and low prices of the Company's Common Stock as reported on the Nasdaq
     National Market System on December 3, 1997. The fee for these shares has
     previously been paid.     
    
(2)  Estimated in accordance with Rule 457(c) solely for the purpose of 
     computing the amount of the registration fee based on the average of the
     high and low prices of the Company's Common Stock as reported on the Nasdaq
     National Market System on April 3, 1998.     

                                _______________

  THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR DATES
AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL FILE
A FURTHER AMENDMENT THAT SPECIFICALLY STATES THAT THIS REGISTRATION STATEMENT
SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(a) OF THE
SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(a),
MAY DETERMINE.
================================================================================
<PAGE>
 
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+INFORMATION CONTAINED HEREIN IS SUBJECT TO COMPLETION OR AMENDMENT. A         +
+REGISTRATION STATEMENT RELATING TO THESE SECURITIES HAS BEEN FILED WITH THE   +
+SECURITIES AND EXCHANGE COMMISSION. THESE SECURITIES MAY NOT BE SOLD NOR MAY  +
+OFFERS TO BUY BE ACCEPTED PRIOR TO THE TIME THE REGISTRATION STATEMENT        +
+BECOMES EFFECTIVE. THIS PROSPECTUS SHALL NOT CONSTITUTE AN OFFER TO SELL OR   +
+THE SOLICITATION OF AN OFFER TO BUY NOR SHALL THERE BE ANY SALE OF THESE      +
+SECURITIES IN ANY STATE IN WHICH SUCH OFFER, SOLICITATION OR SALE WOULD BE    +
+UNLAWFUL PRIOR TO REGISTRATION OR QUALIFICATION UNDER THE SECURITIES LAWS OF  +
+ANY SUCH STATE.                                                               +
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                      
               SUBJECT TO COMPLETION, DATED APRIL 6, 1998      

PROSPECTUS
                                    
                                2,314,286 SHARES      


                                     AVIRON


                                  COMMON STOCK

                              ___________________

    
     This Prospectus relates to 2,314,286 shares of Aviron ("Aviron" or the
"Company") Common Stock, par value $.001 (the "Common Stock"), which are being
offered and sold by a certain stockholder of the Company (the "Selling
Stockholder").  The Selling Stockholder, directly or through agents, broker-
dealers or underwriters, may sell the Common Stock offered hereby from time to
time on terms to be determined at the time of sale, in transactions on the
Nasdaq National Market or in privately negotiated transactions or in a
combination of such methods of sale, at fixed prices that may be changed, at
market prices prevailing at the time of sale, at a price related to such
prevailing prices or at negotiated prices.  The Selling Stockholder may effect
such transactions by selling shares to or through broker-dealers, and such
broker-dealers may receive compensation in the form of discounts, concessions or
commissions from the Selling Stockholder or the purchasers of the shares for
whom such broker-dealers may act as agents or to whom they sell as principal or
both (which compensation to a particular broker-dealer may be in excess of
customary commissions).  The Company will not receive any proceeds from the sale
of shares by the Selling Stockholder.  See "Selling Stockholder" and "Plan of
Distribution."      
    
     The Common Stock of the Company is quoted on the Nasdaq National Market
under the symbol "AVIR." The last reported sales price of the Company's Common
Stock on the Nasdaq National Market on April 3, 1998 was $22.9375 per share.
    
                              ____________________
    
THIS OFFERING INVOLVES A HIGH DEGREE OF RISK. SEE "RISK FACTORS" ON PAGES 9-19.
     
                             _____________________

         THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE
           SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES
           COMMISSION NOR HAS THE SECURITIES AND EXCHANGE COMMISSION
               OR ANY STATE SECURITIES COMMISSION PASSED UPON THE
                 ACCURACY OR ADEQUACY OF THIS PROSPECTUS.  ANY
                      REPRESENTATION TO THE CONTRARY IS A
                               CRIMINAL OFFENSE.


     No underwriting commissions or discounts will be paid by the Company in
connection with this offering.  Estimated expenses payable by the Company in
connection with this offering are $45,000. The aggregate proceeds to the
Selling Stockholder from the Common Stock will be the purchase price of the
Common Stock sold less the aggregate agents' commissions and underwriters'
discounts, if any, and other expenses of issuance and distribution not borne by
the Company. See "Plan of Distribution."

     The Selling Stockholder and any agents, broker-dealers or underwriters that
participate in the distribution of the Common Stock may be deemed to be
"underwriters" within the meaning of the Securities Act of 1933, as amended (the
"Act"), and any commission received by them and any profit on the resale of the
Common Stock purchased by them may be deemed to be underwriting discounts or
commissions under the Act.  The Company has agreed to indemnify the Selling
Stockholder and certain other persons against certain liabilities, including
liabilities under the Act.

The date of this Prospectus is ___________ __, ____


<PAGE>
 
   No person is authorized in connection with any offering made hereby to give
any information or to make any representation not contained or incorporated by
reference in this Prospectus, and any information or representation not
contained or incorporated herein must not be relied upon as having been
authorized by the Company. This Prospectus does not constitute an offer to sell,
or a solicitation of an offer to buy, by any person in any jurisdiction in which
it is unlawful for such person to make such offer or solicitation. Neither the
delivery of this Prospectus at any time nor any sale made hereunder shall, under
any circumstances, imply that the information herein is correct as of any date
subsequent to the date hereof.


                            ADDITIONAL INFORMATION

     A Registration Statement on Form S-3 relating to the Common Stock offered
hereby has been filed by the Company with the Securities and Exchange
Commission. This Prospectus does not contain all of the information set forth in
the Registration Statement and the exhibits and schedules thereto. Statements
contained in this Prospectus as to the contents of any contract or other
document referred to are not necessarily complete and in each instance reference
is made to the copy of such contract or other document filed as an exhibit to
the Registration Statement, each such statement being qualified in all respects
by such reference. For further information with respect to the Company and the
Common Stock offered hereby, reference is made to such Registration Statement,
exhibits and schedules. A copy of the Registration Statement may be inspected by
anyone without charge at the Commission's principal office located at 450 Fifth
Street, N.W., Washington, D.C. 20549, the New York Regional Office located at 7
World Trade Center, 13th Floor, New York, New York 10048, and the Chicago
Regional Office located at Northwestern Atrium Center, 500 West Madison Street,
Chicago, Illinois 60661-2511, and copies of all or any part thereof may be
obtained from the Public Reference Branch of the Commission upon the payment of
certain fees prescribed by the Commission. The Commission maintains a World-Wide
Web site that contains reports, proxy and information statements and other
information regarding registrants that file electronically with the Commission.
The address of the Commission's Web site is http://www.sec.gov.

                            AVAILABLE INFORMATION

     The Company is subject to the informational requirements of the Securities
Exchange Act of 1934, as amended (the "Exchange Act"), and in accordance
therewith files reports and other information with the Securities and Exchange
Commission (the "Commission"). Reports, proxy statements and other information
filed by the Company may be inspected and copied at the public reference
facilities maintained by the Commission at 450 Fifth Street, N.W., Washington,
D.C. 20549 and at the Commission's regional offices located at 7 World Trade
Center, Suite 1300, New York, New York 10048, and at 500 West Madison St., Suite
1400, Chicago, Illinois 60661. Copies may also be obtained from the Public
Reference Section of the Commission at 450 Fifth Street, N.W., Washington, D.C.
20549 at prescribed rates. The Common Stock of the Company is traded on the
Nasdaq National Market. Reports and other information concerning the Company may
be inspected at the National Association of Securities Dealers, Inc., 1735 K
Street, N.W., Washington, D.C. 20006.

                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

     The following documents, filed with the Commission under the Exchange Act 
(File No. 0-20815) are hereby incorporated by reference into this Prospectus:
     
     (a) The Company's Annual Report on Form 10-K for the fiscal year ended
December 31, 1997, filed on March 17, 1998, as amended March 31, 1998, including
all material incorporated by reference therein.     
         
    
     (b) The Company's Proxy Statement for its 1997 Annual Meeting of 
Stockholders, filed April 28, 1997; and     
    
     (c) The Company's Current Report on Form 8-K dated March 17, 1998, filed 
April 1, 1998.     

                                       4
<PAGE>
 
         

     All documents filed by the Company pursuant to Sections 13(a), 13(c), 14 or
15(d) of the Exchange Act after the date of this Prospectus and prior to the
termination of the offering shall be deemed to be incorporated by reference
herein and to be a part hereof from the date of filing of such documents.  Any
statement contained in this Prospectus or in a document incorporated or deemed
to be incorporated by reference herein shall be deemed to be modified or
superseded for purposes of this Prospectus to the extent that a statement
contained herein or in any subsequently-filed document which also is or is
deemed to be incorporated by reference herein modifies or supersedes such
statement.  Any such statement so modified or superseded shall not be deemed,
except as so modified or superseded, to constitute a part of this Prospectus.

     The Company will provide without charge to each person, including any
beneficial owner, to whom this Prospectus is delivered, upon written or oral
request of such person, a copy of any and all of the documents that have been
incorporated by reference herein (not including exhibits to such documents
unless such exhibits are specifically incorporated by reference herein or into
such documents).  Such request may be directed to: Investor Relations, Aviron,
297 North Bernardo Avenue, Mountain View, California 94043.


                                       5
<PAGE>
 
                                    SUMMARY

     This Prospectus contains forward-looking statements which involve risks and
uncertainties.  The Company's actual results could differ materially from those
anticipated in these forward-looking statements as a result of certain factors,
including those set forth under "Risk Factors" and elsewhere in this Prospectus.
    
     The following summary is qualified in its entirety by the more detailed
information, including "Risk Factors," appearing elsewhere in this Prospectus or
incorporated by reference in this Prospectus.      

                                  THE COMPANY
    
     Aviron is a biopharmaceutical company whose focus is the prevention of
disease through innovative vaccine technology. The Company's goal is to become a
leader in the discovery, development, manufacture and marketing of vaccines
which are sufficiently cost effective to justify their use in immunization
programs targeting the general population. Aviron's vaccine programs are based
on both classical live virus vaccine attenuation techniques and the Company's
proprietary genetic engineering technologies. Live virus vaccines, such as those
for smallpox, polio, measles, mumps, rubella and chicken pox, have had a long
record of success in preventing, and in some cases eliminating, disease.

     The Company's lead product candidate, a cold adapted influenza vaccine
delivered as an intranasal spray, has been tested in over 5,000 infants,
children, adults and elderly persons and has been shown to provide a high
protection rate against influenza with minimal adverse effects in a pivotal
Phase III clinical trial in children. Aviron is developing this live vaccine for
widespread annual use in children, healthy adults and high risk adults. The
Company has initiated Phase II clinical trials for a live intranasal vaccine for
Parainfluenza Virus Type 3 ("PIV-3") to protect against croup. The Company also
is developing a subunit vaccine for Epstein-Barr Virus ("EBV") to protect
against mononucleosis, in collaboration with SmithKline Beecham Biologicals,
S.A. ("SmithKline Beecham"), which entered Phase I clinical trials in Europe in
October 1997. Aviron is also using its proprietary Rational Vaccine Design
technologies to discover new live virus vaccines. Rational Vaccine Design
involves the addition of antigenic information to enhance the virus' stimulation
of the immune system, the deletion or modification of virulence proteins, or the
alteration of the virus' genetic control signals to slow down its replication.
The Company is applying these technologies to develop vaccine candidates for
diseases caused by Cytomegalovirus ("CMV"), Herpes Simplex Virus Type 2 ("'HSV-
2") and Respiratory Syncytial Virus ("RSV").      

    
     Influenza.  Influenza affects 35 to 50 million Americans each year
resulting in approximately 20,000 deaths annually, primarily in the elderly,
despite the availability of an injectable inactivated vaccine that has been
reported to be 60% to 90% effective.  The United States Food and Drug
Administration (the "FDA") estimates that approximately 80 million doses of the
injectable influenza vaccine were manufactured for use in the United States in
1997.  Experts suggest that, although over half of Americans at high risk for
complications from influenza receive the annual influenza vaccine, relatively
few of the 70 million children under the age of 18 are vaccinated.      

    
     In July 1997, the National Institute of Allergy and Infectious Diseases
("NIAID") of the National Institutes of Health ("NIH") and the Company announced
the results of an initial analysis of the first stage of a pivotal Phase III
clinical trial of Aviron's live cold adapted intranasal influenza vaccine
involving 1,602 children. In this trial, the vaccine demonstrated a 93%
protection rate against culture-confirmed influenza in those children receiving
two doses of the vaccine, the primary endpoint of the study. Only 1% of the
children who received two doses experienced culture-confirmed influenza,
compared to 18% of those receiving placebo. These results were statistically
significant. The clinical investigators have submitted the findings of this
trial for publication in a peer-reviewed medical journal. The Company is
conducting the second stage of this Phase III clinical trial in 1,358 children
who participated in the first stage of this trial to collect immunogenicity
data, as well as additional safety and efficacy data. In 1996, the Company
completed a challenge efficacy study of this vaccine in 92 adults which
demonstrated an 85% protection rate compared to placebo, against culture-
confirmed influenza. These results were also statistically significant.
Previously, Aviron conducted Phase I/II clinical trials of this vaccine in
approximately 600 children and healthy adults.      

     The cold adapted influenza vaccine elicits an immune response similar to
that of the natural infection by stimulating mucosal immunity in the nose,
cellular components of the immune system and circulating antibodies.  Aviron
intends to

                                       6
<PAGE>
 
develop the live cold adapted influenza vaccine for widespread annual use in
children and adults, and for co-administration with the inactivated injectable
vaccine for improved protection in the elderly.  In addition, Aviron is
developing a genetically engineered influenza vaccine that is intended to be a
better immune stimulus in the elderly than either the cold adapted vaccine or
the inactivated vaccine alone, and, therefore, more suitable for use as a
single-dose vaccine in this population.

     Parainfluenza Virus Type 3.  PIV-3 is a common respiratory virus of
childhood which causes croup, cough, fever and pneumonia.  Over 80% of children
have been infected by age four, many having experienced several cases of PIV-3
infection.  The Company has in-licensed the rights to a bovine PIV-3 ("bPIV-3")
vaccine from the NIH which has been tested in over 100 infants, children and
adults for prevention of PIV-3 illness.  Aviron has submitted an IND for a Phase
II clinical trial which the Company expects to begin by the end of 1997.

     Epstein-Barr Virus.  EBV infects most people at some point in their
lifetime.  At least half of the approximately 10% of students who first become
infected with the virus in high school and college develop infectious
mononucleosis.  EBV also has been shown to be a contributing factor in the
development of certain types of cancer and lymphoma.  The Company has delivered
clinical trial materials to SmithKline Beecham to begin a Phase I clinical
trial of the subunit vaccine, which was initiated by SmithKline Beecham in
Europe in December 1997.

     Cytomegalovirus.  Most people also become infected with CMV at some time in
their lives, but the resulting disease is typically serious only for those with
impaired immune systems or for babies of women infected in the first trimester
of pregnancy.  The Company has selected several Rational Vaccine Design
candidates for clinical testing for the prevention of CMV disease.

     Herpes Simplex Virus Type 2.  Genital herpes is an incurable disease
characterized by recurrent, often painful genital sores, with over 700,000 new
cases estimated in the United States each year.  The company currently is
developing and evaluating several Rational Vaccine Design candidates in
preclinical models to create a prophylactic vaccine.

     Respiratory Syncytial Virus.  RSV is the major cause of lower respiratory
tract illness in the very young, responsible for over 90,000 hospitalizations
and more than 4,000 deaths per year in the United States.  Aviron is using its
Rational Vaccine Design technology to develop intranasal vaccine candidates to
prevent RSV disease.

     Aviron has entered into, and intends to enter into additional, selected
collaborative agreements to gain access to complementary technologies,
capabilities and financial support for its programs.  In addition to acquiring
rights from third parties to augment its Rational Vaccine Design technology and
the cold adapted influenza vaccine technology, the Company has entered into a
collaborative agreement with SmithKline Beecham covering worldwide rights to its
EBV vaccine, and a collaboration with Sang-A Pharm. Co., Ltd. ("Sang-A")
involving certain marketing and manufacturing rights to the Company's products
in Korea.  In addition, the Company entered into a contract manufacturing
agreement with Evans Medical Limited, a subsidiary of Medeva plc ("Evans"), for
the commercial manufacture of its cold adapted influenza vaccine.
    
RECENT DEVELOPMENTS      
    
     In March 1998, $100,000,000 of 5 3/4% Convertible Subordinated Notes due 
2005 (the "Notes") were issued by the Company and sold to "qualified 
institutional buyers" (as defined in Rule 144A of the Securities Act) and a 
limited number of other institutional "accredited investors" (as defined in Rule
501(a)(1), (2), (3) or (7) under the Securities Act) in transactions exempt 
from registration under the Securities Act. The net proceeds to Aviron from the 
sale of the Notes were approximately $96.0 million. Of the net proceeds, 
approximately $13.3 million was used to repurchase 530,831 shares of Aviron 
Common Stock formerly held by Sang-A. The balance is expected to be used for
clinical trials, regulatory submissions, manufacturing and marketing expenses in
support of product launch for its cold adapted influenza vaccine; research and
development, clinical testing, clinical trials and regulatory submissions for
its other vaccine programs; and working capital.     

     The Company was incorporated in California in April 1992 as Vector
Pharmaceuticals, Inc., changed its name to Aviron in February 1993, and
reincorporated in Delaware in November 1996.  The Company's executive offices
are located at 297 North Bernardo Avenue, Mountain View, California 94043, and
its telephone number is (650) 919-6500.

         
                                       7
<PAGE>
 


                                  THE OFFERING

    
Shares offered..................   Up to 2,314,286 Shares, all of which are
                                   being offered by the Selling Stockholder.(1)
                                              
Use of Proceeds.................   The Company will not receive any of the
                                   proceeds from the sale of the Shares by the
                                   Selling Stockholder.
                                   
Nasdaq National Market Symbol...   AVIR.
 
- ------------
    
(1)  1,714,286 shares of Common Stock were issued by the Company pursuant to
     the Common Stock Purchase Agreement between the Company and Biotech Target,
     S.A. dated March 27, 1997; and 600,000 shares of Common Stock were issued
     by the Company pursuant to the conversion of Series C Preferred Stock
     which was purchased in October 1995.      
     

                                       8
<PAGE>
 
                                  RISK FACTORS

     In addition to the other information in this Prospectus, the following risk
factors should be considered carefully in evaluating the Company and its
business before purchasing shares of the Common Stock offered hereby.

UNCERTAINTIES RELATED TO CLINICAL TRIALS
    
     In order to commercialize any of its products under development, the
Company must demonstrate with substantial evidence through clinical trials and
to the FDA's satisfaction that the product is safe and effective for use in the
indications for which approval is requested. The results from preclinical
testing and early clinical trials may not be predictive of results obtained in
large clinical trials. Companies in the pharmaceutical, biopharmaceutical and
biotechnology industries have suffered significant setbacks in various stages of
clinical trials, even in advanced clinical trials after promising results had
been obtained in earlier trials. The Company's vaccines are intended for use
primarily in healthy individuals. To obtain regulatory approval, the Company
must demonstrate safety and efficacy in healthy people, which likely will
require a lengthier process and involve a larger number of trials and people
than would be customary for clinical trials of therapeutics for disease
management. There can be no assurance that the Company's clinical trials will
demonstrate sufficient safety and efficacy to obtain the requisite regulatory
approvals or will result in marketable products. If the Company's cold adapted
influenza vaccine is not shown to be safe and effective in Aviron's future
clinical trials, the resulting delays in obtaining regulatory approvals for this
vaccine, as well as the need for additional financing, would have a material
adverse effect on the Company's business, financial condition and results of
operations. A material incidence of adverse side effects during Aviron's
clinical trials could have a negative impact on the marketing of the product. 
     
    
     The Company's cold adapted influenza vaccine is a trivalent vaccine
delivered as a nasal spray that is based on technology licensed from the NIH and
the University of Michigan. Wyeth-Ayerst licensed certain rights to the vaccine
in 1991 and was developing it for sale in collaboration with the NIH until
relinquishing its rights in 1993. Formulations of the vaccine have been the
subject of a number of clinical trials performed by the NIAID and others. The
Company has reviewed the data from these trials and believes that it can submit
such data in partial support of its application for regulatory approval of its
cold adapted influenza vaccine from the FDA. The Company did not participate in
these trials and cannot be confident in the accuracy of the data collected. Very
few of the trials involved a trivalent vaccine delivered as a nasal spray, but
instead typically used formulations of monovalent or bivalent vaccine delivered
as nasal drops. The Company has performed and is in the process of performing
additional trials of its cold adapted influenza vaccine candidate to support its
application to the FDA. There can be no assurance that the data from these 
third-party trials are accurate, that the Company will be able to obtain
favorable results from its own trials, or that the Company can complete these
trials on a timely basis, or at all.     
    
     In the case of the Company's cold adapted influenza vaccine, the Company is
seeking FDA approval for indications in children, healthy adults, and for co-
administration with the inactivated injectable vaccine in high risk adults,
including the elderly. As a result, the Company's clinical trials will need to
demonstrate to the FDA's satisfaction safety and efficacy of the vaccine in each
of these target populations. The data necessary to calculate the primary
endpoints in the Company's pivotal Phase III clinical trial of its live cold
adapted intranasal influenza vaccine in healthy children became available in
July 1997. There can be no assurance that the analysis of the data regarding the
primary endpoint announced by the Company and the conclusions drawn from this
analysis will not change in the course of regulatory review for licensing. Such
changes could have an adverse effect on the Company's product development
efforts and its prospects for regulatory approval of the vaccine. The Company is
conducting the second stage of its Phase III clinical trial in healthy children
during the 1997/98 influenza season. There can be no assurance that the results
of the second stage of this trial will support the results of the first stage of
this trial. Failure to do so could have an adverse effect on the regulatory
approval or labeling of the cold adapted intranasal influenza vaccine and could
have a material adverse effect on the Company's business, financial condition
and results of operations. In addition, the Company currently plans to submit
safety data to support labeling claims for use of the vaccine in healthy and
high risk adults; however, the Company plans to submit efficacy data on only a
limited number of people for these populations in its initial PLA filing. There
can be no assurance that the FDA will consider this data to be sufficient to
support indications for use of the vaccine in healthy or high risk adults. To
the extent that the FDA does not find such data submitted by the Company
sufficient to support product approval for one or more indications, the
Company's commercialization of the vaccine may be substantially delayed for one
or more of its target populations. In this connection, the Company could be
required to commence and complete additional clinical trials to generate
additional safety and efficacy data to support product approval for one or more
of its target populations.      
    
     The completion of the Company's clinical trials may be delayed by many
factors. For example, delays may be encountered in enrolling a sufficient number
of people fitting the appropriate trial profile, preparing the modified vaccine
strain for certain influenza seasons, or manufacturing clinical trial materials.
The Company's late-stage clinical trials of its live cold adapted influenza
vaccine must be conducted during the influenza season and must be commenced
early enough in the approximately five-month season so that subjects may be
vaccinated well in advance of a challenge by the wild-type virus. Were the
influenza season to commence earlier than anticipated, the number of subjects
that could participate in a particular study might be reduced in that season due
to the subjects' possible exposure to wild-type influenza virus. Additionally,
there is a risk that there will not be enough natural influenza in the community
in a given influenza season to achieve statistically significant results from
clinical trials. There can be no assurance that delays in, or termination of,
clinical trials will not occur. Any delays in, or termination of, the Company's
clinical trial efforts could have a material adverse effect on the Company's
business, financial condition and results of operations.      
    
     There can be no assurance that the Company's development efforts will be
successful, that required regulatory approvals, including those with respect to
IND, PLA and ELA applications, will be obtained or that any products, if
introduced, will be successfully marketed.       

                                       9
<PAGE>
 
         

UNCERTAINTIES RELATED TO EARLY STAGE OF DEVELOPMENT; TECHNOLOGICAL UNCERTAINTY
    
     Aviron commenced its operations in April 1992 and until recently was a
development stage company. All of the Company's product candidates are in the
research or development stage. With the exception of two in-licensed product
candidates, none of the Company's proposed products has yet been approved for
clinical trials. To date, the Company has had no revenue from product sales and
all of its resources have been dedicated to the development of vaccines. There
can be no assurance that product revenues will be realized on a timely basis, if
ever.      
    
     The development of safe and effective live vaccines for the prevention of
viral diseases such as influenza, parainfluenza and other target diseases is
highly uncertain and subject to numerous risks. Potential products that appear
to be promising at early stages of development may not reach the market for a
number of reasons. Potential products may be found ineffective or cause harmful
side effects during preclinical testing or clinical trials, fail to receive
necessary regulatory approvals, be difficult to manufacture on a large scale, be
uneconomical, fail to achieve market acceptance or be precluded from
commercialization by proprietary rights of third parties. Aviron has not yet
requested or received the regulatory approvals that are required to market its
products. Aviron does not expect that any of its proposed products will be ready
for commercialization until at least the 1999/2000 influenza season, if at all.
The Company's estimate of the potential timing of commercialization of its
proposed products is a forward-looking statement that is subject to risks and
uncertainties and actual results may vary materially as a result of a number of
factors. Such factors include those described under "-- Uncertainties Related to
Clinical Trials," " -- Lack of Manufacturing Experience; Reliance on Contract
Manufacturers," and "-- Stability of Cold Adapted Influenza Vaccine." To achieve
profitability, the Company, alone or with others, must successfully identify,
develop, test, manufacture and market its products. There can be no assurance
that Aviron will succeed in the development and marketing of any product. Any
potential product requires significant additional investment, development,
preclinical testing and clinical trials prior to potential regulatory approval
and commercialization.      

         
                                      10
<PAGE>
 
    
NEED FOR ANNUAL REASSORTMENT; LACK OF MANUFACTURING EXPERIENCE; RELIANCE ON
CONTRACT MANUFACTURERS

     Influenza viruses have a high mutation rate and the surface antigens of
influenza viruses that induce protective immunity are variable from year to
year. Each spring, the FDA and CDC determine circulating influenza strains that
will be included in the following season's influenza vaccines. As a result,
manufacturers of vaccines, including Aviron, must modify their influenza
vaccines each year to include the selected strains in a form that meets FDA
guidelines, within an approximately six-month period, in order to make them
available before the influenza season. If the Company were unable to develop an
influenza vaccine for a particular year that meets FDA and CDC guidelines and
establish a manufacturing process for the vaccine, its business, financial
condition and results of operations would be materially adversely affected. No
assurance can be given that delays in preparing vaccines for use in clinical
trials or commercial sales will not be encountered.

     The Company currently does not have facilities to manufacture the cold
adapted influenza vaccine and has no experience with clinical or commercial
manufacture of this potential product. All of the cold adapted vaccine material
used in the Company's early stage clinical trials has been supplied solely by
Evans pursuant to the Evans Clinical Agreement. Evans is one of four companies
licensed by the FDA to produce influenza vaccine for sale in the United States,
and produces its own injectable inactivated influenza vaccine that could compete
with the Company's cold adapted influenza vaccine. Under the Evans Clinical
Agreement, Evans also is collaborating with Aviron to develop a liquid
formulation of the cold adapted influenza vaccine requiring only refrigeration
rather than frozen storage. The Company believes that a liquid formulation will
be required to address markets outside the United States and Canada.

     The Company initially plans to obtain any commercial quantities of its cold
adapted influenza vaccine product from Evans. Pursuant to the Evans Commercial
Agreement, Evans has agreed to manufacture the Company's needs for bulk product
through the 2001/2002 influenza season. In October 1997, the Company entered
into a nonexclusive arrangement with PCI for blending, filling, packaging and
labeling of its cold adapted influenza vaccine in the United States until
October 2004. In the event of better than expected market acceptance, the
Company may be capacity-constrained on its supply of vaccine through at least
the 2000/2001 influenza season. In order to secure future production capacity,
Aviron may extend and expand its existing arrangements, collaborate with other
third parties, or establish its own manufacturing facilities. Using an
alternative supplier or building a proprietary facility would require a
substantial amount of funds and additional clinical trials and testing. There
can be no assurance that an alternative source of supply will be established on
a timely basis, or that the Company will have or be able to obtain funds
sufficient for building or equipping a new facility. In addition, as part of the
regulatory approval process, before commercial launch of the cold adapted
influenza vaccine, the Company will need to obtain approval of an ELA for its
own facility and the PCI facility, and Evans must obtain an ELA for its
facility. Subsequent establishment of alternative sources of supply or
manufacturing would require approval of a subsequent ELA for each such facility.

     The production of the Company's cold adapted influenza vaccine is subject
to the availability of a large number of specific pathogen-free hen eggs, for
which there are currently a limited number of suppliers. The Company has been
purchasing its egg requirement from a single supplier on a purchase order basis,
rather than pursuant to any long term contractual arrangements. Contamination or
disruption of this source of supply would adversely affect the ability to
manufacture the Company's cold adapted influenza vaccine. The production of the
cold adapted influenza vaccine is also subject to the availability of the device
for delivery of the vaccine intranasally. The Company has been purchasing
intranasal delivery devices from a single supplier on a purchase order basis,
rather than pursuant to any long term contractual arrangements. There can be no
assurance that these suppliers will provide timely and adequate supplies of
these product components and raw materials. In addition, the Company depends on
the submission by the delivery device manufacturer of a DMF for separate review
by regulatory authorities. The Company will reference the DMF as part of the PLA
submission for the cold adapted influenza vaccine.

     The production and marketing of influenza vaccine is highly seasonal.
Because most cases of influenza occur in winter, the majority of influenza
vaccinations in the Northern Hemisphere occur between September and December of
a given year. If the Company were unable to develop an influenza vaccine for a
particular year that meets FDA and CDC guidelines, the Company would receive no
revenues from an influenza vaccine for that influenza season, which would
materially adversely affect the Company's business, financial condition and
results of operation, given the relatively fixed nature of its operating
expenses over the short term. Failure of one of the Company's suppliers to
deliver timely and sufficient supplies to the Company, if it caused the Company
to be unable to deliver vaccines during the peak demand period for the influenza
season, would have a disproportionately adverse effect on the Company's
financial results.

     The Company currently does not have facilities to manufacture any of its
other potential products in commercial quantities and has no experience with
commercial manufacture of vaccine products. To manufacture its other potential
products for large-scale clinical trials or on a commercial scale, the Company
may be required to build a large-scale manufacturing facility, which would
require a significant amount of funds. The scale-up of manufacturing for
commercial production would require the Company to develop advanced
manufacturing techniques and rigorous process controls. However, no assurance
can be given as to the ability of the Company to produce commercial quantities
of its potential products in compliance with applicable regulations or at an
acceptable cost, or at all.

     The Company is alternatively considering the use of contract manufacturers
for the commercial production of its other potential products. The Company is
aware of only a limited number of manufacturers which it believes have the
ability and capacity to manufacture its other potential products in a timely
manner. There can be no assurance that the Company would be able to contract
with any of these companies for the manufacture of its products on acceptable
terms, if at all. If the Company enters into an agreement with a third-party
manufacturer, it may be required to relinquish control of the manufacturing
process, which could adversely affect the Company's results of operations.
Furthermore, a third-party manufacturer also will be required to manufacture the
Company's products in compliance with state and federal regulations. Failure of
any such third-party manufacturer to comply with state and federal regulations
and to deliver the required quantities on a timely basis and at commercially
reasonable prices would materially adversely affect the Company's business,
financial condition and results of operations. No assurance can be given that
the Company, alone or with a third party, will be able to make the transition to
commercial production of its potential products successfully, if at all, or that
if successful, the Company will be able to maintain such production.      

    
STABILITY OF COLD ADAPTED INFLUENZA VACCINE     
    
     The Company's current frozen formulation of the cold adapted influenza
vaccine is being designed to meet an acceptable level of stability for the U.S.
market initially targeted by the Company. In addition to its current frozen
formulation, the Company is exploring alternative formulations and presentations
for the vaccine which may enable improved distribution and longer shelf life.
There can be no assurance that the Company will succeed in achieving adequate
product stability for the current frozen formulation of its live cold adapted
influenza vaccine, that the Company's efforts to produce such alternative
formulations will be successful, or that such alternative formulations will
actually enable improved distribution and longer shelf life.     

                                      11
<PAGE>
 
NEED FOR FUTURE FUNDING; UNCERTAINTY OF ACCESS TO CAPITAL
    
     The Company's operations to date have consumed substantial and increasing
amounts of cash. The negative cash flow from operations is expected to continue
and to accelerate in the foreseeable future. The development of the Company's
technology and proposed products will require a commitment of substantial funds
to conduct the costly and time-consuming research, preclinical testing and
clinical trials necessary to develop and optimize such technology and proposed
products, to establish manufacturing, marketing and sales capabilities and to
bring any such products to market. The Company's future capital requirements
will depend upon many factors, including continued scientific progress in the
research and development of the Company's technology and vaccine programs, the
size and complexity of these programs, the ability of the Company to establish
and maintain collaborative arrangements, progress with preclinical testing and
clinical trials, the time and costs involved in obtaining regulatory approvals,
the cost involved in preparing, filing, prosecuting, maintaining and enforcing
patent claims or trade secrets and product commercialization activities.      
    
     The Company anticipates that revenues from existing collaborations and
current balances of cash, cash equivalents and marketable securities, will
enable it to maintain its current and planned operations through 1999. The
estimate of the time period in which these capital resources will be sufficient
to meet the Company's capital requirements is a forward-looking statement that
is subject to risks and uncertainties and the amounts and timing of the
expenditures by the Company may vary materially depending on numerous factors,
such as the status of the Company's research and development efforts, the
regulatory approval process, technological advances, determinations as to
commercial potential, the terms of collaborative agreements entered into by the
Company, the status of competitive products and the possibility of the Company's
construction of a commercial manufacturing facility for its potential products.
In particular, if the Company were to construct and equip such a manufacturing
facility during this period, the Company anticipates that it would likely begin
to make substantial additional capital expenditures in the second half of 1998
and beyond, which may require the Company to seek additional funding. In
addition, the Company's research and development expenditures will vary as
projects are added, extended or terminated and as a result of variations in
funding from existing or future collaborative agreements. The Company is seeking
additional collaborative agreements with corporate partners and may seek
additional funding through public or private equity or debt financing. There can
be no assurance that any additional collaborative agreements will be entered
into or that additional financing will be available on acceptable terms, if at
all. If additional funds are raised by issuing equity securities, further
dilution to stockholders may result. If adequate funds are not available, the
Company may be required to delay, reduce the scope of, or eliminate one or more
of its research or development programs or to obtain funds through collaborative
arrangements with others that may require the Company to relinquish rights to
certain of its technologies, product candidates or products that the Company
would otherwise seek to develop or commercialize itself, which could materially
adversely affect the Company's business, financial condition and results of
operations.      

UNCERTAINTY OF FUTURE PROFITABILITY; ACCUMULATED DEFICIT
    
     The Company has experienced significant and increasing operating losses
since its inception in April 1992. As of December 31, 1997, the Company had an
accumulated deficit of approximately $66.4 million. Aviron has not received any
product revenue to date and does not expect to generate revenues from the sale
of products for several years, if at all. The Company expects to incur
significant and increasing operating losses over at least the next several years
as the Company's research and development efforts, preclinical testing and
clinical trial activities expand. The Company's ability to achieve
profitability, or to refinance its obligations with respect to its indebtedness,
depends in part upon its ability, alone or with others, to complete development
of its proposed products, to obtain required regulatory approvals and to
successfully manufacture and market such products. To the extent that the
Company is unable to obtain third-party funding for expenses, the Company
expects that its increased expenses will result in increased losses from
operations. There can be no assurance that Aviron will obtain required
regulatory approvals or successfully identify, develop, test, manufacture and
market any product candidates, or that the Company will ever achieve product
revenues or profitability. There can be no assurance that the Company's
revenues, operating results, cash flow and capital resources if and once
generated will be sufficient for payment of its indebtedness in the future. In
the absence of such revenues, operating results, cash flow and capital resources
or in the event of any such delays or other problems, the Company could face
substantial liquidity problems and might be required to dispose of material
assets or operations to meet its debt service and other obligations, and there
can be no assurance as to the timing of such sales or the proceeds that the
Company could realize therefrom.     


UNCERTAINTY OF PROTECTION OF PATENTS AND PROPRIETARY RIGHTS; DEPENDENCE ON TRADE
SECRETS
    
     The Company's success will depend in part on its ability to maintain its
technology licenses, maintain trade secrets, obtain patents and operate without
infringing the proprietary rights of others, both in the United States and in
other countries. Since patent applications in the United States are maintained
in secrecy until patents issue and since publication of discoveries in the
scientific or patent literature often lag behind actual discoveries, the Company
cannot be certain that it was the first to make the inventions covered by each
of its pending patent applications or that it was the first to file patent
applications for such inventions. The patent positions of biotechnology and
pharmaceutical companies can be highly uncertain and involve complex legal and
factual questions, and therefore the breadth of claims allowed in biotechnology
and pharmaceutical patents, or their enforceability, cannot be predicted. There
can be no assurance that any of the Company's or its licensors' patents or
patent applications will issue or, if issued, will not be reexamined, reissued,
opposed, challenged, invalidated or circumvented, or that the rights granted
thereunder will provide proprietary protection or competitive advantages to the
Company.      

                                      12
<PAGE>
 
    
     In May 1996, American Cyanamid Company filed an opposition to the grant of
the Company's European patent with claims directed to chimeric negative strand
RNA viruses and to methods of engineering these viruses to express foreign
proteins and antigens. American Cyanamid Company primarily challenges the
breadth of the claims which the Company was granted. Although the Company is
responding to the opposition, no assurance can be given as to the scope of the
claims, if any, which the European Patent Office ultimately will find
patentable. Failure of the Company to prevail in the opposition would impede the
Company's ability to prevent competitors from using this technology in Europe. 
     
    
     The commercial success of Aviron additionally will depend, in part, upon
the Company not infringing patents issued to others. A number of pharmaceutical
companies, biotechnology companies, universities and research institutions have
filed patent applications or received patents in the areas of the Company's
programs. Some of these patent applications or patents may limit the scope of
claims issuing from the Company's patent applications, prevent certain claims
from being issued, or conflict in certain respects with claims made under the
Company's applications.      
    
     The Company is aware of patent applications that have been filed by others
that may pertain to certain aspects of the Company's programs or to its patents
or patent applications, including the patents related to the Company's RSV
vaccine under development. The Company is aware of a claim by a third party,
regarding inventorship of subject matter claimed in a United States patent
which, along with its related foreign counterpart patents and applications, is
licensed to the Company and which is directed to certain aspects of technology
relating to herpes viruses. This claim may also relate to a pending United
States patent application which is a continuation of the licensed patent. It is
presently unclear whether this claim of inventorship is valid, and, if valid, it
could affect ownership of the subject United States patent and patent
application as well as their foreign counterparts.      
    
     If patents have been or are issued to others containing preclusive or
conflicting claims and such claims are ultimately determined to be valid, the
Company may be required to obtain licenses to these patents or to develop or
obtain alternative technology. No assurance can be given that patents have not
been issued, or will not be issued, to third parties that contain preclusive or
conflicting claims with respect to the cold adapted influenza vaccine or any of
the Company's other programs. The Company's breach of an existing license or
failure to obtain a license to technology required to commercialize its products
may have a material adverse effect on the Company's business, financial
condition and results of operations. Litigation, which could result in
substantial costs to the Company, may also be necessary to enforce any patents
issued to the Company or to determine the scope and validity of third-party
proprietary rights. If competitors of the Company prepare and file patent
applications in the United States that claim technology also claimed by the
Company, the Company may have to participate in interference proceedings
declared by the United States Patent and Trademark Office to determine priority
of invention, which could result in substantial cost to the Company, even if the
eventual outcome is favorable to the Company. An adverse outcome could subject
the Company to significant liabilities to third parties and require the Company
to license disputed rights from third parties or to cease using such technology.
     
    
     The patent laws of European and certain other foreign countries generally
do not allow for the issuance of patents for methods of treatment of the human
body. To the extent the Company's patent portfolio includes claims for methods
of treating humans, these methods may not be protectable in Europe and certain
other foreign countries.      
    
     The Company also relies on trade secrets to protect its technology,
especially where patent protection is not believed to be appropriate or
obtainable. Certain of the Company's licensors also rely on trade secrets to
protect technology which has been licensed to Aviron, and as a result, the
Company is dependent on the efforts of such licensors to protect such trade
secrets. For example, the University of Michigan relies, in part, on trade
secrets to protect the master strains of the cold adapted influenza virus used
by the Company and the NIH relies in part on trade secrets to protect the master
strains of the bPIV-3 virus. Aviron protects its proprietary technology and
processes, in part, by confidentiality agreements or material transfer
agreements with its employees, consultants, collaborators and certain
contractors. There can be no assurance that these agreements will not be
breached, that the Company would have adequate remedies for any breach, or that
the Company's trade secrets or those of its licensors will not otherwise become
known or be independently discovered by competitors. To the extent that Aviron
or its consultants or research collaborators use intellectual property owned by
others in their work for the Company, disputes may also arise as to the rights
in related or resulting know-how and inventions. See "-- Lack of Patent
Protection of Cold Adapted Influenza Master Donor Strains."      

    
LACK OF PATENT PROTECTION OF COLD ADAPTED INFLUENZA MASTER DONOR STRAINS

     The Company has no issued patents covering the cold adapted influenza
master donor strains. The Company's rights to the master donor strains are
substantially based on an exclusive worldwide license of materials and know-how
from the University of Michigan, which owns the master donor strains from which
the Company's vaccine is derived, and on an exclusive license of know-how and
clinical trial data from the NIH. Neither the University of Michigan nor the NIH
has been issued any patents covering the cold adapted influenza vaccine. There
can be no assurance that a third party will not gain access by some means to
University of Michigan master donor strains, reproduce the Company's cold
adapted influenza vaccine or develop another live virus influenza vaccine which
might be comparable to Aviron's in terms of safety and effectiveness. See "--
Uncertainty of Protection of Patents and Proprietary Rights; Dependence on Trade
Secrets."      

                                      13
<PAGE>
 
         

GOVERNMENT REGULATION; NO ASSURANCE OF REGULATORY APPROVALS
    
     The production and marketing of the Company's products and its ongoing
research and development activities are subject to extensive regulation by
numerous government authorities in the United States and other countries. Prior
to marketing in the United States, any product developed by the Company must
undergo rigorous preclinical testing and clinical trials and an extensive
regulatory approval process implemented by the FDA under the Food, Drug and
Cosmetic Act. Satisfaction of such regulatory requirements, which includes
demonstrating that the product is both safe and effective, typically takes
several years or more depending upon the type, complexity and novelty of the
product and requires the expenditure of substantial resources. This process may
be more demanding for vaccines intended for use in healthy people compared to
therapeutics used for treatment of people with diseases. Preclinical studies
must be conducted in compliance with the FDA's Good Laboratory Practice
regulations. Clinical testing must meet requirements for Institutional Review
Board oversight and informed consent, as well as FDA prior review, oversight and
Good Clinical Practice regulations. The Company has limited experience in
conducting and managing the clinical trials necessary to obtain regulatory
approval. Furthermore, the Company or the FDA may suspend clinical trials at any
time if either believes that the subjects participating in such trials are being
exposed to unacceptable health risks.      
    
     The Company understands that its vaccine products will be classified by the
FDA as "biologic products," as opposed to "drug products." The steps ordinarily
required before a biologic product may be marketed in the United States include
(a) preclinical testing and clinical trials; (b) the submission to the FDA of an
IND, which must become effective before clinical trials may commence; (c)
adequate and well-controlled clinical trials to establish the safety and
efficacy of the drug; (d) the submission to the FDA of a PLA, together with an
ELA for each manufacturing facility; and (e) FDA approval of the applications,
including approval of all product labeling.      
    
     Preclinical testing includes laboratory evaluation of product chemistry,
formulation and stability, as well as animal studies to assess the potential
safety and efficacy of each product. The results of the preclinical tests are
submitted to the FDA as part of an IND and are reviewed by the FDA before the
commencement of clinical trials. Unless the FDA objects to an IND, the IND will
become effective 30 days following its receipt by the FDA. There can be no
assurance that submission of an IND will result in FDA authorization to commence
clinical trials or that the lack of an objection means that the FDA will
ultimately approve an application for marketing approval.      
    
     Before receiving FDA approval to market a product in accordance with the
above procedures, the Company will have to demonstrate that the product is safe
and effective. Data obtained from preclinical testing and clinical trials are
susceptible to varying interpretations which could delay, limit or prevent
regulatory approvals. In addition, delays or rejections may be encountered based
upon additional government regulation from future legislation or administrative
action or changes in FDA policy during the period of product development,
clinical trials and FDA regulatory review. Similar delays may also be
encountered in foreign countries. There can be no assurance that even after such
time and expenditures, regulatory approval will be obtained for any products
developed by the Company. If regulatory approval of a product is granted, such
approval and related labeling claims will be limited to those specific segments
of the population for which the product is safe and effective, as demonstrated
through clinical trials. Furthermore, approval may entail ongoing requirements
for post-marketing studies. Even if such regulatory approval is obtained, a
marketed product, its manufacturer and its manufacturing facilities are subject
to continual review and periodic inspections. The regulatory standards for
manufacturing are currently being applied stringently by the FDA. Discovery of
previously unknown problems with a product, manufacturer or facility may result
in restrictions on such product or manufacturer, including costly recalls or
even withdrawal of the product from the market. There can be no assurance that
any product developed by the Company alone or in conjunction with others will
prove to be safe and efficacious in clinical trials and will meet all of the
applicable regulatory requirements needed to receive or maintain marketing
approval.      
    
     The Company believes that the approval process for vaccines may be longer
than for therapeutic products, since vaccines are administered to healthy
individuals. In addition, regulatory scrutiny may be particularly intense for
products, such as Aviron's cold adapted influenza vaccine, which are designed to
be given to healthy children.      
    
     Outside the United States, the Company's ability to market a product is
contingent upon receiving marketing authorization from the appropriate
regulatory authorities. The requirements governing the conduct of clinical
trials, marketing authorization, pricing and reimbursement vary widely from
country to country. At present, foreign marketing authorizations are applied for
at a national level, although within the European Union (the "EU"), procedures
are available to companies wishing to market a product in more than one EU
member state. If the regulatory authorities are satisfied that adequate evidence
of safety, quality and efficacy has been presented, a marketing authorization
will be granted. This foreign regulatory approval process includes all of the
risks associated with FDA approval set forth above.      

                                      14
<PAGE>

         
 
UNCERTAINTY OF MARKET ACCEPTANCE
    
     Even if the requisite regulatory approvals are obtained for the Company's
potential products, uncertainty exists as to whether such products will be
accepted in United States or foreign markets. The Company believes, for example,
that widespread use of the Company's proposed vaccines in the United States is
unlikely without positive recommendations from the ACIP, the AAP or the American
College of Physicians. There can be no assurance that such authorities will
recommend the use of the Company's proposed products. The lack of such
recommendations would have a material adverse effect on the Company's business,
financial condition and results of operations.      
    
     A number of additional factors may affect the rate and overall market
acceptance of Aviron's cold adapted influenza vaccine and any other products
which may be developed by the Company, including the safety and efficacy results
in the Company's clinical trials, the rate of adoption of Aviron's vaccines by
health care practitioners, the rate of vaccine acceptance by the target
population, the success of the CDC in selecting proper strains to be included in
each season's vaccine and the perceived effectiveness of influenza vaccines
generally, the timing of market entry relative to competitive products, the
availability of alternative technologies, the price of the Company's products
relative to alternative technologies, the means and frequency of administration
of such products, the availability of third-party reimbursement and the extent
of marketing and sales efforts by the Company, collaborative partners and third-
party distributors or agents retained by the Company. Side effects, such as the
runny nose, sore throat or fever seen in a minority of clinical trial
participants, or unfavorable publicity concerning Aviron's products or any
product incorporating live virus vaccines could have an adverse effect on the
Company's ability to obtain physician, patient or third-party payor acceptance
and efforts to sell the Company's products. The Company's current formulation of
the cold adapted influenza vaccine requires frozen storage, which may adversely
affect market acceptance in certain foreign countries where adequate freezer
capacity is not commonly available. There can be no assurance that physicians,
patients or third-party payors will accept new live virus vaccine products or
any of the Company's products as readily as other types of vaccines, or at all.
     

LACK OF MARKETING EXPERIENCE; DEPENDENCE ON THIRD PARTIES
    
     Primary care physicians, including pediatricians, family practitioners,
general practitioners, and internists, are expected to play a major role in
influencing decisions by individuals to obtain influenza prophylaxis for
themselves or their children and the choice of type of immunization. For the
cold adapted influenza vaccine to be widely adopted, it will likely be necessary
to engage the efforts of an experienced pharmaceutical sales force, in addition
to obtaining recommendations for the vaccine's use from advisory bodies such as
the ACIP and AAP. Aviron currently has no direct sales or distribution
capability nor does it intend to build a large pharmaceutical sales force
itself. Rather, the Company intends to obtain these services through
collaboration with one or more major pharmaceutical companies in the United
States and elsewhere. The Company is currently evaluating the capabilities of a
number of such potential partners and expects to conclude one or more agreements
as part of its commercialization strategy. No assurance can be given that the
Company will be successful in negotiating an arrangement in a timely fashion or
that such an agreement will be on favorable terms to the Company.      
    
     The successful commercialization of the Company's products is dependent in
part upon the ability of the Company to maintain existing and enter into
additional collaborative agreements with corporate partners for the development,
testing and marketing of certain of its vaccines and upon the ability of these
third parties to perform their responsibilities. The amount and timing of
resources devoted to these activities is not within the control of the Company.
There can be no assurance that any such agreements or arrangements will be
available on terms acceptable to the Company, if at all, that such third parties
would perform their obligations as expected, or that any revenue would be
derived from such arrangements. If Aviron is not able to enter into such
agreements or arrangements, it could encounter delays in introducing its
products into the market or be forced to limit the scope of its
commercialization activities. If the Company were to market products directly,
significant additional expenditures, management resources and time would be
required to develop a sales and marketing staff within the Company. In addition,
the Company would also be competing with other companies that currently have
experienced and well-funded marketing and sales operations. There can be no
assurance that the Company will be able to establish its own sales and marketing
force or that any such force, if established, would be successful in gaining
market acceptance for any products that may be developed by the Company.      


INTENSE COMPETITION AND RISK OF TECHNOLOGICAL OBSOLESCENCE
    
     The Company operates in a rapidly evolving field. Any product developed by
the Company would compete with existing and new drugs and vaccines being created
by pharmaceutical, biopharmaceutical and biotechnology companies. If the Company
were able to successfully develop its vaccines, it would be competing with
larger companies that have already introduced vaccines and have significantly
greater marketing, sales, manufacturing, financial and managerial resources. For
example, with respect to its cold adapted influenza vaccine, the Company will be
competing against larger companies such as Pasteur Merieux Connaught, Wyeth-
Ayerst, and Evans, the supplier of the Company's cold adapted influenza vaccine.
Each of these companies sells the injectable inactivated influenza vaccine in
the United States, has significantly greater financial resources than Aviron and
has established marketing and distribution channels for such products. In
addition the Company is aware of efforts to develop improved inactivated
injectable influenza vaccines by Chiron (Chiron Biocine Division) and others;
intranasally administered inactivated vaccines by Swiss Serum and Vaccine
Institute, Biovector Therapeutics, S.A. and Virus Research Institute; a "naked
DNA" vaccine by Merck Research Laboratories; and a commercially available cold
adapted influenza vaccine in Russia. Further, the Company is aware of several
large pharmaceutical companies that alone or with partners are developing new
drug therapies designed to relieve the symptoms of influenza. The Company is
also aware of several companies that are marketing or are in late-stage
development of products to prevent CMV or HSV disease, including Glaxo Wellcome
plc ("Glaxo"), and a cold adapted PIV-3 vaccine developed with NIH support which
is licensed to Wyeth-Ayerst.      

                                       15
<PAGE>
         
     
     New developments are expected to continue in the pharmaceutical,
biopharmaceutical and biotechnology industries and in academia, government
agencies and other research organizations. Other companies may succeed in
developing products that are safer, more effective or less costly than any that
may be developed by the Company. Such companies may also be more effective than
the Company in the production and marketing of their products. Furthermore,
rapid technological development by competitors may result in the Company's
products becoming obsolete before the Company is able to recover its research,
development or commercialization expenses incurred in connection with any such
product. Many potential competitors have substantially greater financial,
technical, marketing and sales resources than the Company. Some of these
companies also have considerable experience in preclinical testing, clinical
trials and other regulatory approval procedures. Moreover, certain academic
institutions, government agencies and other research organizations are
conducting research in areas in which the Company is working. These institutions
are becoming increasingly aware of the commercial value of their findings and
are becoming more active in seeking patent protection and licensing arrangements
to collect royalties for the use of technology that they have developed. These
institutions may also market competitive commercial products on their own or
through joint ventures.      
    
     Aviron believes that competition in the markets it is addressing will
continue to be intense. The vaccine industry is characterized by intense price
competition, and the Company anticipates that it will face this and other forms
of competition. There can be no assurance that pharmaceutical, biopharmaceutical
and biotechnology companies will not develop more effective products than those
of the Company or will not market and sell their products more effectively than
the Company, which would have a material adverse effect on the Company's
business, financial condition and results of operations.      

DEPENDENCE ON COLLABORATIVE AGREEMENTS
    
     The Company's strategy for the development, clinical trials, manufacturing
and commercialization of certain of its products includes maintaining and
entering into various collaborations with corporate partners, licensors,
licensees and others. The Company in-licensed its cold adapted influenza vaccine
from the NIAID and the University of Michigan. It has obtained rights to certain
recombinant negative strand RNA technology from Mount Sinai, and rights to the
herpes simplex viruses, EBV and various recombinant methods and materials from
ARCH. The Company has entered into agreements with SmithKline Beecham for the
development of its EBV vaccine, with Sang-A for clinical development,
manufacturing and development rights for certain products in Korea and certain
Asian countries (not including Japan), and has licensed from the NIAID rights
covering its PIV-3 vaccine. There can be no assurance that the Company will be
able to maintain existing collaborative agreements, negotiate collaborative
arrangements in the future on acceptable terms, if at all, or that any such
collaborative arrangements will be successful. To the extent that the Company is
not able to maintain or establish such arrangements, the Company would be
required to undertake product development and commercialization activities at
its own expense, which would increase the Company's capital requirements or
require the Company to limit the scope of its development and commercialization
activities. In addition, the Company may encounter significant delays in
introducing its products into certain markets or find that the development,
manufacture or sale of its products in such markets is adversely affected by the
absence of such collaborative agreements. ARCH has recently asserted an
interpretation of the financial terms of this agreement with the Company,
relating to the license by Aviron of its EBV technology to SmithKline Beecham,
which would require the Company to pay ARCH one-half of any future or past
payments (including sub-license fees and milestone payments) received by Aviron
under the SB Agreement. The Company disputes ARCH's interpretation of the
financial terms of the agreement. No assurance can be given, however, that the
Company's interpretation will prevail. Failure of the Company to prevail in this
matter could have a material adverse effect on the Company's business, financial
condition and results of operations.      

                                       16
<PAGE>
         
     
     The Company cannot control the amount and timing of resources which its
collaborative partners devote to the Company's programs or potential products,
which may vary, because of factors unrelated to the potential products. If any
of the Company's collaborative partners breach or terminate their agreements
with the Company or otherwise fail to conduct their collaborative activities in
a timely manner, the preclinical or clinical development or commercialization of
product candidates or research programs will be delayed and the Company would be
required to devote additional resources to product development and
commercialization, or terminate certain development programs. These
relationships generally may be terminated at the discretion of the Company's
collaborative partners, in some cases with only limited notice to the Company.
The termination of collaborative arrangements could have a material adverse
effect on the Company's business, financial condition and results of operations.
There also can be no assurance that disputes will not arise in the future with
respect to the ownership of rights to any technology developed with third
parties. These and other possible disagreements between collaborators and the
Company could lead to delays in the collaborative research, development or
commercialization of certain product candidates, or could result in litigation
or arbitration, which would be time consuming and expensive, and would have a
material adverse effect on the Company's business, financial condition and
results of operations.      
    
     In addition, Aviron's collaborative partners may develop, either alone or
with others, products that compete with the development and marketing of the
Company's products. Competing products of the Company's collaborative partners
may result in their withdrawal of support with respect to all or a portion of
the Company's technology, which would have a material adverse effect on the
Company's business, financial condition and results of operations.      

VOLATILITY OF COMMON STOCK PRICE

     The market prices for securities of pharmaceutical, biopharmaceutical and
biotechnology companies have historically been highly volatile. The market from
time to time experiences significant price and volume fluctuations that are
unrelated to the operating performance of particular companies. In addition,
factors such as fluctuations in the Company's operating results, future sales of
Common Stock, announcements of technological innovations or new therapeutic
products by the Company or its competitors, announcements regarding
collaborative agreements, clinical trial results, government regulation,
developments in patent or other proprietary rights, public concern as to the
safety of drugs developed by the Company or others, changes in reimbursement
policies, comments made by securities analysts and general market conditions can
have an adverse effect on the market price of the Common Stock. In particular,
the realization of any of the risks described in these "Risk Factors" could have
a significant and adverse impact on such market price.

POTENTIAL ADVERSE EFFECTS OF SHARES ELIGIBLE FOR FUTURE SALE

     Sales of a substantial amount of Common Stock in the public market
following this offering could adversely affect the market price for the
Company's Common Stock.  

                                       17
<PAGE>
     
Of the shares outstanding, all are freely tradable without restriction or
further registration under the Securities Act, except for (i) 747,481 shares
held by directors and executive officers of the Company, (ii) up to 3,235,827
shares of Common Stock issuable upon conversion of the Notes and (iii) the
shares being registered pursuant to this Form S-3.     

RISK OF PRODUCT LIABILITY; UNCERTAINTY OF AVAILABILITY OF INSURANCE

     The Company's business exposes it to potential product liability risks that
are inherent in the testing, manufacturing and marketing of vaccines.  The
Company has obtained clinical trial liability insurance for its clinical trials,
but there can be no assurance that it will be able to maintain adequate
insurance for its clinical trials.  The Company also intends to seek product
liability insurance in the future for products approved for marketing, if any.
However, no assurance can be given that the Company will be able to acquire or
maintain insurance or that insurance can be acquired or maintained at a
reasonable cost or in sufficient amounts to protect the Company.  There can be
no assurance that insurance coverage and the resources of the Company would be
sufficient to satisfy any liability, resulting from product liability claims.  A
successful product liability, claim or series of claims brought against the
Company could have a material adverse effect on its business, financial
condition and results of operations.  The Company intends to seek inclusion of
certain of its products in the United States National Vaccine Injury
Compensation Program, a no-fault compensation program for claims against vaccine
manufacturers, which administers a trust funded by excise taxes on sales of
certain recommended childhood vaccines.  There can be no assurance that this
government program will continue or that the Company's proposed vaccines will be
included in the program.

UNCERTAINTY RELATED TO PHARMACEUTICAL PRICING AND REIMBURSEMENT

     Political, economic and regulatory influences are subjecting the health
care industry in the United States to fundamental change.  Recent initiatives to
reduce the federal deficit and to reform health care delivery are increasing
cost-containment efforts.  The Company anticipates that Congress, state
legislatures and the private sector will continue to review and assess
alternative benefits, controls on health care spending through limitations on
the growth of private health insurance premiums and Medicare and Medicaid
spending, the creation of large insurance purchasing groups, price controls on
pharmaceuticals and other fundamental changes to the health care delivery
system.  Any such proposed or actual changes could cause the Company or its
collaborative partners to limit or eliminate spending on development projects.
Legislative debate is expected to continue in the future, and market forces are
expected to demand reduced costs.  Aviron cannot predict what effect the
adoption of any federal or state health care reform measures or future private
sector reforms may have on its business.

     In both domestic and foreign markets, sales of the Company's proposed
vaccines will depend in part upon the availability of reimbursement from third-
party payors, such as government health administration authorities, managed care
providers, private health insurers and other organizations.  In addition, other
third-party payors are increasingly challenging the price and cost effectiveness
of medical products and services.  Significant uncertainty exists as to the
reimbursement status of newly approved health care products.  There can be no
assurance that the Company's proposed products will be considered cost effective
or that adequate third-party reimbursement will be available to enable Aviron to
maintain price levels sufficient to realize an appropriate return on its
investment in product development.  Legislation and regulations affecting the
pricing of pharmaceuticals may change before the Company's proposed products are
approved for marketing.  Adoption of such legislation could further limit
reimbursement for medical products.  If adequate coverage and

                                       18
<PAGE>
 
reimbursement levels are not provided by the government and third-party payors
for the Company's potential products, the market acceptance of these products
would be adversely affected, which would have a material adverse effect on the
Company's business, financial condition and results of operations.

NEED TO ATTRACT AND RETAIN KEY EMPLOYEES AND CONSULTANTS

     The Company is highly dependent on the principal members of its scientific
and management staff.  In addition, the Company relies on consultants and
advisors, including its scientific advisors, to assist the Company in
formulating its research and development strategy.  Attracting and retaining
qualified personnel, consultants and advisors will be critical to the Company's
success.  To pursue its product development and marketing plans, the Company
will be required to hire additional qualified scientific personnel to perform
research and development, as well as personnel with expertise in conducting
clinical trials, government regulation, manufacturing, marketing and sales.
Expansion in the areas of product development, marketing and sales is also
expected to require the addition of management personnel and the development of
additional expertise by existing management personnel.  The Company faces
competition for qualified individuals from numerous pharmaceutical,
biopharmaceutical and biotechnology companies, universities and other research
institutions.  There can be no assurance that the Company will be able to
attract and retain such individuals.
    
     In addition, a portion of the Company's research and development is
conducted under sponsored research programs with several universities and
research institutions. The Company depends on the availability of a principal
investigator for each such program, and the Company cannot assure that these
individuals or their research staffs will be available to conduct research and
development for Aviron. The Company's academic collaborators are not employees
of the Company. As a result, the Company has limited control over their
activities and can expect that only limited amounts of their time will be
dedicated to Company activities. The Company's academic collaborators may have
relationships with other commercial entities, some of which could compete with
the Company.      

RISKS ASSOCIATED WITH HAZARDOUS MATERIALS

     The Company's research and development involves the controlled use of
hazardous materials, chemicals, various radioactive substances and viruses.
Although the Company believes that its safety procedures for handling and
disposing of such materials comply with the standards prescribed by state and
federal regulations, the risk of accidental contamination or injury from these
materials cannot be completely eliminated.  In the event of such an accident,
the Company could be held liable for any damages that result and any such
liability could exceed the resources of the Company and could have a material
adverse effect on the Company's business, financial condition and results of
operations.  The Company may incur substantial costs to comply with
environmental regulations if the Company develops manufacturing capacity.

DILUTION; ABSENCE OF DIVIDENDS

     Investors purchasing shares of Common Stock in this offering will incur
dilution to the extent outstanding options and warrants are exercised. Under an
agreement with the University of Michigan, the Company is obligated to issue a
warrant to purchase shares of Common Stock at an exercise price of $10.00 per
share, for a number of shares to be based on 1.25% of the Common Stock
outstanding on the date, if any, of the first commercial sale of the Company's
cold adapted intranasal influenza vaccine. Investors will incur additional
dilution to the extent this warrant is issued and exercised. See "Dilution." The
Company has not paid any dividends on its Common Stock since inception and does
not anticipate paying any cash dividends in the foreseeable future. See
"Dividend Policy."

ANTI-TAKEOVER EFFECTS OF DELAWARE LAW AND CERTAIN CHARTER PROVISIONS
    
     The Company's Board of Directors has the authority to issue up to 5,000,000
shares of Preferred Stock and to determine the price, rights, preferences and
privileges of those shares without any further vote or action by the Company's
stockholders.  The rights of the holders of Common Stock will be subject to, and
may be adversely affected by, the rights of the holders of any Preferred Stock
that may be issued in the future.  While the Company has no present intention to
issue shares of Preferred Stock, such issuance, while providing desirable
flexibility in connection with possible acquisitions and other corporate
purposes, could have the effect of making it more difficult for a third party to
acquire a majority of the outstanding voting stock of the Company.  In October
1997, the Company's Board of Directors adopted a Share Purchase Rights Plan,
commonly referred to as a "poison pill."  In addition, the Company is subject to
the anti-takeover provisions of Section 203 of the Delaware General Corporation
Law, which prohibits the Company from engaging in a "business combination" with
an "interested stockholder" for a period of three years after the date of the
transaction in which the person became an interested stockholder, unless the
business combination is approved in a prescribed manner. The application of
Section 203 could have the effect of delaying or preventing a change of control
of the Company. The Company's Certificate of Incorporation provides for
staggered terms for the members of the Board of Directors. The staggered Board
of Directors and certain other provisions of the Company's Certificate of
Incorporation and Bylaws may have the effect of delaying or preventing changes
in control or management of the Company, which could adversely affect the market
price of the Company's Common Stock.     

                                       19
<PAGE>
 
                                USE OF PROCEEDS

     The Company will not receive any proceeds from the sale of Common Stock by
the Selling Stockholder in the offering.

                                DIVIDEND POLICY

     Aviron has never paid any cash dividends on its Common Stock.  The Company
presently intends to retain earnings for use in its business and therefore does
not anticipate paying cash dividends in the foreseeable future.

                                      20 
<PAGE>
 
                              SELLING STOCKHOLDER
    
     The following table sets forth the name of the Selling Stockholder, the
number of shares of Common Stock owned beneficially by the Selling Stockholder
as of January 31, 1998 and the number of shares which may be offered pursuant
to this Prospectus.  This information is based upon information provided by the
Selling Stockholder.  The Selling Stockholder may sell all, some or none of
their Common Stock being offered.      

<TABLE>     
<CAPTION>
                          SHARES BENEFICIALLY      NUMBER      SHARES BENEFICIALLY
                             OWNED PRIOR TO       OF SHARES        OWNED AFTER
                              OFFERING(1)           BEING         OFFERING(1)(3)
                         ----------------------               ----------------------
<S>                      <C>         <C>          <C>         <C>        <C>
NAME                      NUMBER     PERCENT(2)    OFFERED     NUMBER    PERCENT(2)
- ----                     ---------   -------      ---------   --------   --------
 
Biotech Target, S.A....  2,655,286    16.50%      2,314,286    341,000     2.12%
</TABLE>      

(1) The entity named in the table has sole voting and investment power with
    respect to all shares beneficially owned.
    
(2) Applicable percentage of ownership is based on 16,094,350 shares of Common
    Stock outstanding on March 17, 1998. Assumes the sale of all shares
    offered hereby. See "Plan of Distribution."      

(3) Assumes the sale of all shares offered hereby.


                              PLAN OF DISTRIBUTION
    
     The Company is registering the shares of Common Stock offered by the
Selling Stockholder hereunder pursuant to contractual registration rights
contained in the Common Stock Purchase Agreement between Aviron and Biotech
Target, S.A. executed on March 27, 1997 (the "Stock Purchase Agreement") and the
Amended and Restated Investors Rights Agreement, which Biotech Target, S.A. 
executed on October 31, 1995 (the "Investors Rights Agreement"). Sales
may be made on the Nasdaq National Market or in private transactions or in a
combination of such methods of sale, at fixed prices that may be changed, at
market prices prevailing at the time of sale, at prices related to such
prevailing market prices or at negotiated prices. The Selling Stockholder may
from time to time enter into short sales and use the shares registered hereunder
to cover such short positions. The Selling Stockholder may effect such
transactions by selling shares to or through broker-dealers, and such broker-
dealers may receive compensation in the form of discounts, concessions or
commissions from the Selling Stockholder or the purchasers of the shares for
whom such broker-dealers may act as agents or to whom they sell as principal or
both (which compensation to a particular broker-dealer may be in excess of
customary commissions). The Selling Stockholder and any persons who participate
in the distribution of the Common Stock offered hereby may be deemed to be
underwriters within the meaning of the Act, and any discounts, commissions or
concessions received by them and any provided pursuant to the sale of shares 
by them might be deemed to be underwriting discounts and commissions under the 
Act.     

     In order to comply with the securities laws of certain states, if
applicable, the Common Stock may be sold in such jurisdictions only through
registered or licensed brokers or dealers.  In addition, in certain states the
Common Stock may not be sold unless it has been registered or qualified for sale
or an exemption from registration or qualification requirements is available and
is complied with.
    
     The Company has agreed in the Stock Purchase Agreement and the Investors
Rights Agreement to register the shares of Aviron Common Stock received by the
Selling Stockholder pursuant to both such agreements under applicable Federal
and state securities laws under certain circumstances and at certain times.
Pursuant to such agreements, the Company has filed a registration statement
related to the shares offered hereby and has agreed to keep such registration
statement effective until the earlier of (i) March 27, 1999; or (ii) the sale of
all the securities registered thereunder or (iii) such time as all shares may be
sold without restriction under Rule 144. The Company will pay substantially all
of the expenses incident to the offering and sale of the Common Stock to the
public, other than commissions, concessions and discounts of underwriters,
dealers or agents. Such expenses (excluding such commissions and discounts), 
are estimated to be $45,000. The Stock Purchase Agreement and the Investors 
Rights Agreement provides for cross-indemnification of the Selling Stockholder 
and      

                                      21
<PAGE>
 
the Company to the extent permitted by law, for losses, claims, damages,
liabilities and expenses arising, under certain circumstances, out of any
registration of the Common Stock.

                                 LEGAL MATTERS
    
     The validity of the issuance of the Common Stock offered hereby will be
passed upon for the Company by Cooley Godward LLP, Palo Alto, California.
Cooley Godward LLP possesses a warrant for 16,666 shares of the Company's
Common Stock. Certain attorneys at Cooley Godward LLP who have performed
services for the Company own approximately an aggregate of 2,080 shares of
Common Stock.      

                                    EXPERTS
    
     The financial statements of Aviron appearing in Aviron's Annual Report 
(Form 10-K), as amended, for the year ended December 31, 1997 have been audited
by Ernst & Young LLP, independent auditors, as set forth in their report
included therein and incorporated herein by reference. Such financial statements
are incorporated herein by reference in reliance upon such report given upon the
authority of such firm as experts in accounting and auditing.     

                                      22
<PAGE>
 
===========================================================        
                                                                   
NO DEALER, SALES REPRESENTATIVE OR ANY OTHER PERSON HAS 
BEEN AUTHORIZED IN CONNECTION WITH THIS OFFERING MADE 
HEREBY TO GIVE ANY INFORMATION OR TO MAKE ANY REPRESENTATION 
OTHER THAN THOSE CONTAINED IN THIS PROSPECTUS AND, IF GIVEN 
OR MADE, SUCH INFORMATION AND REPRESENTATION MUST NOT BE 
RELIED UPON AS HAVING BEEN AUTHORIZED BY THE COMPANY.  THIS 
PROSPECTUS DOES NOT CONSTITUTE AN OFFER TO SELL, OR 
SOLICITATION OF AN OFFER TO BUY, SECURITIES OTHER THAN THE 
REGISTERED SECURITIES TO WHICH IT RELATES OR AN OFFER TO, OR 
SOLICITATION OF, ANY PERSON IN ANY JURISDICTION WHERE AN OFFER 
OR SOLICITATION WOULD BE UNLAWFUL.  NEITHER THE DELIVERY OF 
THIS PROSPECTUS NOR ANY OFFER OR SALE MADE HEREUNDER SHALL, 
UNDER ANY CIRCUMSTANCES, CREATE ANY IMPLICATION THAT THERE HAS 
BEEN NO CHANGE IN THE AFFAIRS OF THE COMPANY SINCE THE DATE 
HEREOF OR THAT THE INFORMATION CONTAINED HEREIN IS CORRECT 
AS OF ANY TIME SUBSEQUENT TO THE DATE HEREOF.

                 ------------------------                          
                                                                   
                   TABLE OF CONTENTS                               
                                                                   
                                             PAGE                  
                                             ----                  
Available Information.......................   4
Additional Information......................   4                    
Incorporation of Certain                                           
  Documents by Reference....................   4                    
Risk Factors................................   9                    
Use of Proceeds.............................  20                     
Dividend Policy.............................  20                     
Selling Stockholder.........................  21                     
Plan of Distribution........................  21                     
Legal Matters...............................  22                     
Experts.....................................  22                     
                                                                   
===========================================================        

===========================================================
                                                                    
                        2,314,286 SHARES      
                                                                
                             AVIRON                             
                                                                
                           COMMON STOCK                         
                                                                
                                                                
                     ----------------------                     
                                                                
                            PROSPECTUS                          
                                                                
                     -----------------------                    
                                                                
                             
                             ________, 1998      
                                                                
                                                                
===========================================================

<PAGE>

                                    PART II
                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

     The following table sets forth the expenses payable by the Registrant in
connection with the sale, issuance and distribution of the securities being
registered, other than underwriting discounts and commissions.  All amounts are
estimates except the SEC registration fee.  None of these expenses will be paid
by the Selling Securityholder.

     SEC Registration Fee..............   $15,000
     Printing Expenses.................     5,000
     Legal Fees and Expenses...........    15,000
     Accounting Fees and Expenses......    10,000

     Total.............................   $45,000
                                           ------

ITEM 15.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     Under Section 145 of the Delaware General Corporation Law, Aviron has broad
powers to indemnify its directors and officers against liabilities they may
incur in such capacities, including liabilities under the Act.  Aviron's Bylaws
also provide that the Registrant will indemnify its directors and executive
officers and may indemnify its other officers, employees and agents to the
fullest extent not prohibited by Delaware General Corporation Law.

     Aviron's Certificate of Incorporation provides for the elimination of
liability for monetary damages for breach of the directors' fiduciary duty of
care to Aviron and its stockholders.  These provisions do not eliminate the
director's duty of care, and in appropriate circumstances, equitable remedies
such as injunctive or other forms of non-monetary relief will remain available
under Delaware law.  In addition, each director will continue to be subject to
liability for breach of the director's duty of loyalty to the Company, for acts
or omissions not in good faith or involving intentional misconduct or a knowing
violation of law, for any transaction from which the director derived an
improper personal benefit and for payment of dividends or approval of stock
repurchases or redemptions that are unlawful under Delaware Law.  The provision
also does not affect a director's responsibilities under any other laws, such as
the federal securities laws or state or federal environmental laws.

                                     II-1
<PAGE>
 
ITEM 16. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES.


<TABLE>         
<CAPTION> 
 EXHIBIT
  NUMBER           DESCRIPTION OF DOCUMENT
 -------           -----------------------
 <C>         <S> 
   1.1       Form of Underwriting Agreement.(1)
   3.1       Bylaws of the Registrant. (2)
   3.2       Restated Certificate of Incorporation of the Registrant. (2)
   4.1       Reference is made to Exhibits 3.1 and 3.2.
   4.2       Specimen Stock Certificate. (1)
   4.3       Warrant for Series A Preferred Stock, issued to The Mount Sinai
             School of Medicine of the City of New York. (1)
   4.4       Warrant for Series A Preferred Stock, issued to The Mount Sinai
             School of Medicine of the City of New York. (1)
   4.5       Warrant for Series A Preferred Stock, issued to The Mount Sinai
             School of Medicine of the City of New York. (1)
   4.6       Warrant for Series A Preferred Stock, issued to The Mount Sinai
             School of Medicine of the City of New York. (1)
   4.7       Warrant for Series C Preferred Stock, issued to Raymond, James &
             Associates. (1)
   4.8       Investors Rights Agreement, dated July 18, 1995, among the 
             Registrant and the investors named thereon. (1)
   4.9       Common Stock Purchase Agreement between the Registrant and Biotech
             Target, S.A., dated as of March 27, 1997. (3)
   4.10      Rights Agreement between the Registrant and BankBoston, N.A., dated
             as of October 8, 1997.(5)
   4.11      Registration Rights Agreement dated as of March 15, 1998 by and
             among Aviron and the initial purchasers of 5 3/4% Convertible
             Subordinated Notes due 2005 (the "Notes")
   4.12      Indenture dated as of March 15, 1998 between Aviron and Marine 
             Midland Bank as Trustee for the Notes.
   4.13      Purchase Agreement dated as of March 24, 1998 by and among Aviron 
             and the initial purchasers of the Notes.
   5.1       Opinion of Cooley Godward LLP.
 +10.1       License Agreement between the Registrant and ARCH Development 
             Corporation, dated July 1, 1992. (1)
 +10.2       Technology Transfer Agreement between the Registrant and The Mount
             Sinai School of Medicine of the City University of New York, dated 
             February 9, 1993. (1)
 +10.3       Materials Transfer and Intellectual Property Agreement between the
             Registrant and the Regents of the University of Michigan, dated
             February 24, 1995. (1)
 +10.4       Stock Transfer Agreement between the Registrant and the Regents of
             the University of Michigan, dated February 24, 1995. (1)
 +10.5       Development and License Agreement between the Registrant and Sang-A
             Pharm. Co., Ltd., dated May 3, 1995. (1)
 +10.6       Cooperative Research and Development Agreement, between the
             Registrant and the National Institute of Health, dated May 30, 1995
             (1)
 +10.7       Heads of Agreement between the Registrant and SmithKline Beecham 
             Biologicals S.A., dated October 8, 1995. (1)
 +10.8       Manufacturing and Development Agreement between the Registrant and
             Evans Medical Limited, dated November 7, 1995. (1)
  10.9       1996 Equity Incentive Plan. (1)
  10.10      1996 Non-Employee Directors' Stock Option Plan. (1)
  10.11      1996 Employee Stock Purchase Plan. (1)
  10.12      Industrial Lease between the Registrant and the Vanni Business Park
             General Partnership, dated August 29, 1995. (1)
 +10.13      First Amendment to License Agreement between the Registrant and 
             ARCH Development Corporation, dated March 15, 1996. (1)
 +10.14      Biological Materials License Agreement between the Registrant and 
             the National Institutes of Health, dated May 31, 1996. (1)
 +10.15      Contract Manufacture Agreement between the Registrant and Evans
             Medical Limited, dated as of April 16, 1997. (4)
++10.16      Production Agreement between the Registrant and Packaging 
             Coordinators, Inc. dated as of October 31, 1997. (6)
  10.17      Facility Reservation Agreement between the Registrant and Packaging
             Coordinators, Inc. dated as of October 31, 1997. (6)
  23.1       Consent of Ernst & Young LLP, Independent Auditors. 
  23.2       Consent of Cooley Godward LLP. Reference is made to 
             Exhibit 5.1.
  27.1       Restated EPS Basic and Diluted for Third Quarter 1996
  27.2       Restated EPS Basic and Diluted for First Quarter 1997
  27.3       Restated EPS Basic and Diluted for Second Quarter 1997
  27.4       Restated EPS Basic and Diluted for Third Quarter 1997
</TABLE>      
- ------------------
 +    Confidential treatment has been granted for portions of this exhibit
++    Confidential treatment has been requested for portions of this exhibit.
(1)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Registration Statement on Form S-1, File No. 333-05209, filed
      June 5, 1996, as amended.
(2)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Quarterly Report on Form 10-Q for the quarter ended September
      30, 1996, File No. 0-20815, filed December 20, 1996.
(3)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Quarterly Report on Form 10-Q for the quarter ended March 31, 
      1997, File No. 0-20815, filed May 15, 1997. 
(4)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Current Report on Form 8-K File No. 0-20815, dated April 16, 
      1997 and filed July 21, 1997. 
(5)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Current Report on Form 8-K File No. 0-20815, dated October 8, 
      1997 and filed October 10, 1997. 
    
(6)   Previously filed with this Registration Statement.      

ITEM 17. UNDERTAKINGS.

     The undersigned Registrant hereby undertakes:

(1)  To file, during any period in which offers or sales are being made, a post-
     effective amendment to this registration statement to include any material
     information with respect to the plan of distribution not previously
     disclosed in the registration statement or any material change to such
     information in the registration statement;

(2)  That, for purposes of determining any liability under the Securities Act,
     each such post-effective amendment shall be deemed to be a new registration
     statement relating to the securities offered therein, and the offering of
     such securities at that time shall be deemed to be the initial bona fide
     offering thereof; and

(3)  To remove from registration by means of a post-effective amendment any of
     the securities being registered which remain unsold at the termination of
     the offering.

     The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or 15(d) of the Securities
Exchange Act of 1934 (and, where applicable, each filing of an employee benefit
plan's annual report pursuant to Section 15(d) of the Securities Exchange Act of
1934) that is incorporated by reference in the registration statement shall be
deemed to be a new registration statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

     Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to directors, officers and controlling persons of the
Registrant pursuant to provisions described in Item 15, or otherwise, the
Registrant has been advised that in the opinion of the Securities and Exchange
Commission such indemnification is against public policy as expressed in the
Securities Act and is, therefore, unenforceable.  In the event that a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Securities
Act and will be governed by the final adjudication of such issue.

                                     II-2
<PAGE>
 
                                   SIGNATURES
        
     Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-3 and has duly caused this Amendment No. 2 to
the Registration Statement to be signed on its behalf by the undersigned,
thereunto duly authorized, in the City of Palo Alto, State of California, on
April 6, 1998.      
         
                                         AVIRON


                                         By /s/ J. Leighton Read, M.D.
                                           _____________________________________
                                              J. Leighton Read, M.D.
                                              Chairman of the Board &
                                              Chief Executive Officer
                                              (Principal Executive Officer)

         
    
     Pursuant to the requirements of the Securities Act, this Amendment No. 2 to
the Registration Statement has been signed below by the following persons in the
capabilities and on the date indicated.      

<TABLE>     
<CAPTION>
          SIGNATURE                            TITLE                           DATE
          ---------                            -----                           ----
<S>                              <C>                                       <C>
 
/s/ J. Leighton Read, M.D.       Chairman of the Board & Chief             April 6, 1998
- ------------------------------   Executive Officer (Principal Executive
J. Leighton Read, M.D.           Officer)
 
/s/ Fred Kurland                 Chief Financial Officer (Principal        April 6, 1998
- ------------------------------   Financial and Accounting Officer)
Fred Kurland

    *                            Director                                  April 6, 1998
- ------------------------------
Reid W. Dennis

    *                            Director                                  April 6, 1998
- ------------------------------
Paul H. Klingenstein

    *                            Director                                  April 6, 1998
- ------------------------------
Bernard Roizman, Sc.D.

    *                            Director                                  April 6, 1998
- ------------------------------
L. James Strand, M.D.

    *                            Director                                  April 6, 1998
- -----------------------------
Jane E. Shaw, Ph.D.


*By: /s/ J. Leighton Read, M.D.
     --------------------------
     J. Leighton Read, M.D.
        Attorney-in-Fact
</TABLE>       

                                     II-3
<PAGE>
 
                              INDEX TO EXHIBITS

<TABLE>         
<CAPTION> 
 EXHIBIT
  NUMBER           DESCRIPTION OF DOCUMENT
 -------           -----------------------
 <C>         <S> 
   1.1       Form of Underwriting Agreement.(1)
   3.1       Bylaws of the Registrant. (2)
   3.2       Restated Certificate of Incorporation of the Registrant. (2)
   4.1       Reference is made to Exhibits 3.1 and 3.2.
   4.2       Specimen Stock Certificate. (1)
   4.3       Warrant for Series A Preferred Stock, issued to The Mount Sinai
             School of Medicine of the City of New York. (1)
   4.4       Warrant for Series A Preferred Stock, issued to The Mount Sinai
             School of Medicine of the City of New York. (1)
   4.5       Warrant for Series A Preferred Stock, issued to The Mount Sinai
             School of Medicine of the City of New York. (1)
   4.6       Warrant for Series A Preferred Stock, issued to The Mount Sinai
             School of Medicine of the City of New York. (1)
   4.7       Warrant for Series C Preferred Stock, issued to Raymond, James &
             Associates. (1)
   4.8       Investors Rights Agreement, dated July 18, 1995, among the 
             Registrant and the investors named thereon. (1)
   4.9       Common Stock Purchase Agreement between the Registrant and Biotech
             Target, S.A., dated as of March 27, 1997. (3)
   4.10      Rights Agreement between the Registrant and BankBoston, N.A., dated
             as of October 8, 1997.(5)
   4.11      Registration Rights Agreement dated as of March 15, 1998 by and
             among Aviron and the initial purchasers of 5 3/4% Convertible
             Subordinated Notes due 2005 (the "Notes")
   4.12      Indenture dated as of March 15, 1998 between Aviron and Marine 
             Midland Bank as Trustee for the Notes.
   4.13      Purchase Agreement dated as of March 24, 1998 by and among Aviron 
             and the initial purchasers of the Notes.
   5.1       Opinion of Cooley Godward LLP.
 +10.1       License Agreement between the Registrant and ARCH Development 
             Corporation, dated July 1, 1992. (1)
 +10.2       Technology Transfer Agreement between the Registrant and The Mount
             Sinai School of Medicine of the City University of New York, dated 
             February 9, 1993. (1)
 +10.3       Materials Transfer and Intellectual Property Agreement between the
             Registrant and the Regents of the University of Michigan, dated
             February 24, 1995. (1)
 +10.4       Stock Transfer Agreement between the Registrant and the Regents of
             the University of Michigan, dated February 24, 1995. (1)
 +10.5       Development and License Agreement between the Registrant and Sang-A
             Pharm. Co., Ltd., dated May 3, 1995. (1)
 +10.6       Cooperative Research and Development Agreement, between the
             Registrant and the National Institute of Health, dated May 30, 1995
             (1)
 +10.7       Heads of Agreement between the Registrant and SmithKline Beecham 
             Biologicals S.A., dated October 8, 1995. (1)
 +10.8       Manufacturing and Development Agreement between the Registrant and
             Evans Medical Limited, dated November 7, 1995. (1)
  10.9       1996 Equity Incentive Plan. (1)
  10.10      1996 Non-Employee Directors' Stock Option Plan. (1)
  10.11      1996 Employee Stock Purchase Plan. (1)
  10.12      Industrial Lease between the Registrant and the Vanni Business Park
             General Partnership, dated August 29, 1995. (1)
 +10.13      First Amendment to License Agreement between the Registrant and 
             ARCH Development Corporation, dated March 15, 1996. (1)
 +10.14      Biological Materials License Agreement between the Registrant and 
             the National Institutes of Health, dated May 31, 1996. (1)
 +10.15      Contract Manufacture Agreement between the Registrant and Evans
             Medical Limited, dated as of April 16, 1997. (4)
++10.16      Production Agreement between the Registrant and Packaging 
             Coordinators, Inc. dated as of October 31, 1997. (6)
  10.17      Facility Reservation Agreement between the Registrant and Packaging
             Coordinators, Inc. dated as of October 31, 1997. (6)
  23.1       Consent of Ernst & Young LLP, Independent Auditors. 
  23.2       Consent of Cooley Godward LLP. Reference is made to 
             Exhibit 5.1.
  27.1       Restated EPS Basic and Diluted for Third Quarter 1996
  27.2       Restated EPS Basic and Diluted for First Quarter 1997
  27.3       Restated EPS Basic and Diluted for Second Quarter 1997
  27.4       Restated EPS Basic and Diluted for Third Quarter 1997
</TABLE>      
- ------------------
 +    Confidential treatment has been granted for portions of this exhibit
++    Confidential treatment has been requested for portions of this exhibit.
(1)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Registration Statement on Form S-1, File No. 333-05209, filed
      June 5, 1996, as amended.
(2)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Quarterly Report on Form 10-Q for the quarter ended September
      30, 1996, File No. 0-20815, filed December 20, 1996.
(3)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Quarterly Report on Form 10-Q for the quarter ended March 31, 
      1997, File No. 0-20815, filed May 15, 1997. 
(4)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Current Report on Form 8-K File No. 0-20815, dated April 16, 
      1997 and filed July 21, 1997. 
(5)   Incorporated by reference to the correspondingly numbered exhibit to the
      Company's Current Report on Form 8-K File No. 0-20815, dated October 8, 
      1997 and filed October 10, 1997. 
    
(6)   Previously filed with this Registration Statement.      


<PAGE>
 
                                                                    EXHIBIT 4.11


        THIS REGISTRATION RIGHTS AGREEMENT is made and entered into as of March
15, 1998 by and among Aviron, a Delaware corporation ("the Company"), and Morgan
Stanley & Co. Incorporated, Bear, Stearns & Co. Inc., Credit Suisse First Boston
Corporation and Hambrecht & Quist LLC (the "Initial Purchasers") pursuant to the
Purchase Agreement, dated as of March 24, 1998 (the "Purchase Agreement"), among
the Company and the Initial Purchasers. In order to induce the Initial
Purchasers to enter into the Purchase Agreement, the Company has agreed to
provide the registration rights set forth in this Agreement. The execution of
this Agreement is a condition to the closing under the Purchase Agreement.

        The Company agrees with the Initial Purchasers, (i) for their benefit as
Initial Purchasers and (ii) for the benefit of the beneficial owners (including
the Initial Purchasers) from time to time of the Notes (as defined herein) and
the beneficial owners from time to time of the Underlying Common Stock (as
defined herein) issued upon conversion of the Notes (each of the foregoing a
"Holder" and together the "Holders"), as follows:

        SECTION 1.  Definitions. Capitalized terms used herein without
definition shall have their respective meanings set forth in the Purchase
Agreement. As used in this Agreement, the following terms shall have the
following meanings:

        Affiliate: With respect to any specified person, an "affiliate," as
defined in Rule 144, of such person.

        Amendment Effectiveness Deadline Date:  See Section 2(d) hereof.

        Applicable Conversion Price: The Applicable Conversion Price as of any
date of determination means the Conversion Price in effect as of such date of
determination or, if no Notes are then outstanding, the Conversion Price that
would be in effect were Notes then outstanding.

        Business Day: Each Monday, Tuesday, Wednesday, Thursday and Friday that
is not a day on which banking institutions in The City of New York or San Jose,
California are authorized or obligated by law or executive order to close.

        Common Stock: The shares of common stock $0.001 par value of the Company
and any other shares of common stock as may constitute "Common Stock" for
purposes of the Indenture, including the Underlying Common Stock.

        Conversion Price: Conversion Price shall have the meaning assigned such
term in the Indenture.
<PAGE>
 
        Damages Accrual Period:  See Section 2(e) hereof.

        Damages Payment Date: Each interest payment date under the Indenture in
the case of Notes, and each April 1 and October 1 in the case of the Underlying
Common Stock.

        Deferral Notice: See Section 3(i) hereof.

        Deferral Period:  See Section 3(i) hereof.

        Effectiveness Deadline Date:  See Section 2(a) hereof.

        Effectiveness Period: The period of two years from the later of (a) the
Issue Date (b) the last date of original issuance of the Notes, or such shorter
period ending on the date that all Registrable Securities have ceased to be
Registrable Securities.

        Event:  See Section 2(e) hereof.

        Event Termination Date:  See Section 2(e) hereof.

        Event Date:  See Section 2(e) hereof.

        Exchange Act: The Securities Exchange Act of 1934, as amended, and the
rules and regulations of the SEC promulgated thereunder.

        Filing Deadline Date:  See Section 2(a) hereof.

        Holder:  See the second paragraph of this Agreement.

        Indenture: The Indenture dated as of the date hereof between the Company
and Marine Midland Bank, as trustee, pursuant to which the Notes are being
issued.

        Initial Purchasers: Morgan Stanley & Co. Incorporated, Bear, Stearns &
Co., Inc., Credit Suisse First Boston Corporation and Hambrecht & Quist LLC

        Initial Shelf Registration Statement:  See Section 2(a) hereof.

        Issue Date:  March 30, 1998.

        Liquidated Damages Amount:  See Section 2(e) hereof.

        Losses:  See Section 6 hereof.

        Material Event: See Section 3(i) hereof.

                                       2
<PAGE>
 
        Notes: The 5 3/4% Convertible Subordinated Notes due 2005 of the Company
to be purchased pursuant to the Purchase Agreement.

        Notice and Questionnaire: A written notice delivered to the Company
containing substantially the information called for by the Selling
Securityholder Notice and Questionnaire attached as Appendix B to the Offering
Memorandum of the Company issued March 24, 1998 relating to the Notes.

        Notice Holder:  On any date, any Holder that has delivered a Notice and
Questionnaire to the Company on or prior to such date.

        Prospectus: The prospectus included in any Registration Statement
(including, without limitation, a prospectus that discloses information
previously omitted from a prospectus filed as part of an effective registration
statement in reliance upon Rule 430A promulgated under the Securities Act), as
amended or supplemented by any amendment or prospectus supplement, including
post-effective amendments, and all materials incorporated by reference or
explicitly deemed to be incorporated by reference in such Prospectus.

        Purchase Agreement:  See the first paragraph of this Agreement.

        Record Holder: (i) With respect to any Damages Payment Date relating to
any Notes as to which any such Liquidated Damages Amount has accrued, the holder
of record of such Note on the record date with respect to the interest payment
date under the Indenture on which such Damages Payment Date shall occur and (ii)
with respect to any Damages Payment Date relating to the Underlying Common Stock
as to which any such Liquidated Damages Amount has accrued, the registered
holder of such Underlying Common Stock fifteen (15 )days prior to the next
succeeding Damages Payment Date.

        Registrable Securities: The Notes until such Notes have been converted
or exchanged into the Underlying Common Stock, and, at all times subsequent to
any such conversion or exchange, any securities into or for which such
Underlying Common Stock have been converted or exchanged, and any security
issued with respect thereto upon any stock dividend, split or similar event
until, in the case of any such security, (A) the earliest of (i) its effective
registration under the Securities Act and resale in accordance with the
Registration Statement covering it, (ii) expiration of the holding period that
would be applicable thereto under Rule 144(k) were it not held by an affiliate
of the Company or (iii) its sale to the public pursuant to Rule 144, and (B) as
a result of the event or circumstance described in any of the foregoing clauses
(i) through (iii), the legends with respect to transfer restrictions required
under the Indenture are removed or removable in accordance with the terms of the
Indenture.

                                       3
<PAGE>
 
        Registration Expenses:  See Section 5 hereof.

        Registration Statement: Any registration statement of the Company that
covers any of the Registrable Securities pursuant to the provisions of this
Agreement, including the Prospectus, amendments and supplements to such
registration statement, including post-effective amendments, all exhibits, and
all materials incorporated by reference or explicitly deemed to be incorporated
by reference in such registration statement.

        Restricted Securities:  As this term is defined in Rule 144.

        Rule 144: Rule 144 under the Securities Act, as such Rule may be amended
from time to time, or any similar rule or regulation hereafter adopted by the
SEC.

        Rule 144A: Rule 144A under the Securities Act, as such Rule may be
amended from time to time, or any similar rule or regulation hereafter adopted
by the SEC.

        SEC:  The Securities and Exchange Commission.

        Securities Act: The Securities Act of 1933, as amended, and the rules
and regulations promulgated by the SEC thereunder.

        Shelf Registration Statement:  See Section 2(a) hereof.

        Subsequent Shelf Registration Statement:  See Section 2(b) hereof.

        TIA:  The Trust Indenture Act of 1939, as amended.

        Trustee: Marine Midland Bank (or any successor entity), the Trustee
under the Indenture.

        Underlying Common Stock: The Common Stock into which the Notes are
convertible or issued upon any such conversion.

        SECTION 2.  Shelf Registration. (a) The Company shall prepare and file
or cause to be prepared and filed with the SEC, as soon as practicable but in
any event by the date (the "Filing Deadline Date") ninety (90) days after the
Issue Date, a Registration Statement for an offering to be made on a delayed or
continuous basis pursuant to Rule 415 of the Securities Act (a "Shelf
Registration Statement") registering the resale from time to time by Holders
thereof of all of the Registrable Securities (the "Initial Shelf Registration
Statement"). The Initial Shelf Registration Statement shall be on Form S-3 or
another appropriate form permitting registration of such Registrable Securities
for resale by such Holders in accordance with the methods of distribution
elected by the Holders and set forth in the Initial Shelf Registration
Statement. The Company shall use its commercially reasonable efforts to cause
the Initial Shelf Registration Statement to be declared effective under the
Securities Act as promptly as is practicable but in any event by

                                       4
<PAGE>
 
the date (the "Effectiveness Deadline Date") that is one hundred eighty (180)
days after the Issue Date, and to keep the Initial Shelf Registration Statement
(or any Subsequent Shelf Registration Statement) continuously effective under
the Securities Act until the expiration of the Effectiveness Period.  At the
time the Initial Shelf Registration Statement is declared effective, each Holder
that became a Notice Holder on or prior to the date ten (10) Business Days prior
to such time of effectiveness shall be named as a selling securityholder in the
Initial Shelf Registration Statement and the related Prospectus in such a manner
as to permit such Holder to deliver such Prospectus to purchasers of Registrable
Securities in accordance with applicable law.  None of the Company's security
holders (other than the Holders of Registrable Securities) shall have the right
to include any of the Company's securities in the Shelf Registration Statement.

       (b) If the Initial Shelf Registration Statement or any Subsequent Shelf
Registration Statement ceases to be effective for any reason at any time during
the Effectiveness Period (other than because all Registrable Securities
registered thereunder shall have been resold pursuant thereto or shall have
ceased to be Registrable Securities), the Company shall use its commercially
reasonable efforts to obtain the prompt withdrawal of any order suspending the
effectiveness thereof, and in any event shall within thirty (30) days of such
cessation of effectiveness amend the Shelf Registration Statement in a manner
reasonably expected to obtain the withdrawal of the order suspending the
effectiveness thereof, or file an additional Shelf Registration Statement
covering all of the securities that as of the date of such filing are
Registrable Securities (a "Subsequent Shelf Registration Statement").  If a
Subsequent Shelf Registration Statement is filed, the Company shall use
commercially reasonable efforts to cause the Subsequent Shelf Registration
Statement to become effective as promptly as is practicable after such filing
and to keep such Registration Statement (or subsequent Shelf Registration
Statement) continuously effective until the end of the Effectiveness Period.

       (c) The Company shall supplement and amend the Shelf Registration
Statement if required by the rules, regulations or instructions applicable to
the registration form used by the Company for such Shelf Registration Statement,
if required by the Securities Act or, to the extent to which the Company does
not reasonably object, as reasonably requested by the Initial Purchasers or by
the Trustee on behalf of the registered Holders or by any Managing Underwriter
in the event of an Underwritten Offering.

       (d) Each Holder of Registrable Securities agrees that if such Holder
wishes to sell Registrable Securities pursuant to a Shelf Registration Statement
and related Prospectus, it will do so only in accordance with this Section 2(d)
and Section 3(i). Each Holder of Registrable Securities wishing to sell
Registrable Securities pursuant to a Shelf Registration Statement and related
Prospectus agrees to deliver a Notice and Questionnaire to the Company at least
three (3) Business Days prior to any intended distribution of Registrable
Securities under the Shelf Registration Statement. From and after the date the
Initial Shelf Registration Statement is declared effective, the Company shall,
as promptly as is practicable after the date a Notice and Questionnaire is
delivered, and in any event within five (5) Business Days after such date, (i)
if

                                       5
<PAGE>
 
required by applicable law, file with the SEC a post-effective amendment to the
Shelf Registration Statement or prepare and, if required by applicable law, file
a supplement to the related Prospectus or a supplement or amendment to any
document incorporated therein by reference or file any other required document
so that the Holder delivering such Notice and Questionnaire is named as a
selling securityholder in the Shelf Registration Statement and the related
Prospectus in such a manner as to permit such Holder to deliver such Prospectus
to purchasers of the Registrable Securities in accordance with applicable law
and, if the Company shall file a post-effective amendment to the Shelf
Registration Statement, use commercially reasonable efforts to cause such post-
effective amendment to be declared effective under the Securities Act as
promptly as is practicable, but in any event by the date (the "Amendment
Effectiveness Deadline Date") that is forty-five (45) days after the date such
post-effective amendment is required by this clause to be filed; (ii) provide
such Holder copies of any documents filed pursuant to Section 2(d)(i); and (iii)
notify such Holder as promptly as practicable after the effectiveness under the
Securities Act of any post-effective amendment filed pursuant to Section
2(d)(i); provided, that if such Notice and Questionnaire is delivered during a
Deferral Period, the Company shall so inform the Holder delivering such Notice
and Questionnaire and shall take the actions set forth in clauses (i), (ii) and
(iii) above upon expiration of the Deferral Period in accordance with Section
3(i).  Notwithstanding anything contained herein to the contrary, the Company
shall be under no obligation to name any Holder that is not a Notice Holder as a
selling securityholder in any Registration Statement or related Prospectus.

       (e) The parties hereto agree that the Holders of Registrable Securities
will suffer damages, and that it would not be feasible to ascertain the extent
of such damages with precision, if the Initial Shelf Registration Statement has
not been filed on or prior to the Filing Deadline Date, (ii) the Initial Shelf
Registration Statement has not been declared effective under the Securities Act
on or prior to the Effectiveness Deadline Date, (iii) the Company has failed to
perform its obligations set forth in Section 2(d) within the time period
required therein, (iv) the aggregate duration of Deferral Periods in any period
exceeds the number of days permitted in respect of such period pursuant to
Section 3(i) hereof or (v) the number of Deferral Periods in any period exceeds
the number permitted in respect of such period pursuant to Section 3(i) (each of
the events of a type described in any of the foregoing clauses (i) through (v)
are individually referred to herein as an "Event," and the Filing Deadline Date
in the case of clause (i), the Effectiveness Deadline Date in the case of clause
(ii), the date by which the Company is required to perform its obligations set
forth in Section 2(d) in the case of clause (iii) (including the filing of any
post-effective amendment prior to the Amendment Effectiveness Deadline Date),
the date on which the aggregate duration of Deferral Periods in any period
exceeds the number of days permitted by Section 3(i) hereof in the case of
clause (iv), and the date of the commencement of a Deferral Period that causes
the limit on the number of Deferral Periods in any period under Section 3(i)
hereof to be exceeded in the case of clause (v), being referred to herein as an
"Event Date"). Events shall be deemed to continue until the "Event Termination
Date," which shall be the following dates with respect to the respective types
of Events: the date the Initial Shelf Registration Statement is filed in the
case of an Event of the type described in clause (i), the date

                                       6
<PAGE>
 
the Initial Shelf Registration Statement is declared effective under the
Securities Act in the case of an Event of the type described in clause (ii), the
date the Company performs its obligations set forth in Section 2(d) in the case
of an Event of the type described in clause (iii) (including, without
limitation, the date the relevant post-effective amendment to the Shelf
Registration Statement is declared effective under the Securities Act),
termination of the Deferral Period that caused the limit on the aggregate
duration of Deferral Periods in a period set forth in Section 3(i) to be
exceeded in the case of the commencement of an Event of the type described in
clause (iv), and termination of the Deferral Period the commencement of which
caused the number of Deferral Periods in a period permitted by Section 3(i) to
be exceeded in the case of an Event of the type described in clause (v).

        Accordingly, commencing on (and including) any Event Date and ending on
(but excluding) the next date on which there are no Events that have occurred
and are continuing (a "Damages Accrual Period"), the Company agrees to pay, as
liquidated damages and not as a penalty, an amount (the "Liquidated Damages
Amount"), payable on the Damages Payment Dates to Record Holders of Notes that
are Registrable Securities and of shares of Underlying Common Stock issued upon
conversion of Notes that are Registrable Securities, as the case may be,
accruing, for each portion of such Damages Accrual Period beginning on and
including a Damages Payment Date (or, in respect of the first time that the
Liquidated Damages Amount is to be paid to Holders on a Damages Payment Date as
a result of the occurrence of any particular Event, from the Event Date) and
ending on but excluding the first to occur of (A) the date of the end of the
Damages Accrual Period or (B) the Next Damages Payment Date, at a rate per annum
equal to one-half of one percent (0.5%) of the aggregate principal amount of
such Notes and the Applicable Conversion Price of such shares of Underlying
Common Stock, as the case may be, in each case determined as of the Business Day
immediately preceding the next Damages Payment Date; provided, that in the case
of a Damages Accrual Period that is in effect solely as a result of an Event of
the type described in clause (iii) of the immediately preceding paragraph, such
Liquidated Damages Amount shall be paid only to the Holders that have delivered
Notice and Questionnaires that caused the Company to incur the obligations set
forth in Section 2(d) the non-performance of which is the basis of such Event;
provided further, that any Liquidated Damages Amount accrued with respect to any
Note or portion thereof called for redemption on a redemption date or converted
into Underlying Common Stock on a conversion date prior to the Damages Payment
Date, shall, in any such event, be paid instead to the Holder who submitted such
Note or portion thereof for redemption or conversion on the applicable
redemption date or conversion date, as the case may be, on such date (or
promptly following the conversion date, in the case of conversion).
Notwithstanding the foregoing, no Liquidated Damages Amounts shall accrue as to
any Registrable Security from and after the earlier of (x) the date such
security is no longer a Registrable Security and (y) expiration of the
Effectiveness Period. The rate of accrual of the Liquidated Damages Amount with
respect to any period shall not exceed the rate provided for in this paragraph
notwithstanding the occurrence of multiple concurrent Events. Following the cure
of all Events requiring the payment by the Company of Liquidated Damages Amounts
to the Holders of Registrable Securities pursuant to this Section, the accrual
of Liquidated Damages

                                       7
<PAGE>
 
Amounts will cease (without in any way limiting the effect of any subsequent
Event requiring the payment of Liquidated Damages Amount by the Company).

        The Trustee shall be entitled, on behalf of Holders of Notes or
Underlying Common Stock, to seek any available remedy for the enforcement of
this Agreement, including for the payment of any Liquidated Damages Amount.
Notwithstanding the foregoing, the parties agree that the sole damages payable
for a violation of the terms of this Agreement with respect to which liquidated
damages are expressly provided shall be such liquidated damages. Nothing shall
preclude a Notice Holder or Holder of Registrable Securities from pursuing or
obtaining specific performance or other equitable relief with respect to this
Agreement.

        All of the Company's obligations set forth in this Section 2(e) that are
outstanding with respect to any Registrable Security at the time such security
ceases to be a Registrable Security shall survive until such time as all such
obligations with respect to such security have been satisfied in full
(notwithstanding termination of this Agreement pursuant to Section 8(k)).

        The parties hereto agree that the liquidated damages provided for in
this Section 2(e) constitute a reasonable estimate of the damages that may be
incurred by Holders of Registrable Securities by reason of the failure of the
Shelf Registration Statement to be filed or declared effective or available for
effecting resales of Registrable Securities in accordance with the provisions
hereof.

        Section 3.  Registration Procedures. In connection with the registration
obligations of the Company under Section 2 hereof, the Company shall:

       (a) Before filing any Registration Statement or Prospectus or any
amendments or supplements thereto with the SEC, furnish to the Initial
Purchasers copies of all such documents proposed to be filed and use reasonable
efforts to reflect in each such document when so filed with the SEC such
comments as the Initial Purchasers reasonably shall propose within five (5)
Business Days of the delivery of such copies to the Initial Purchasers.

       (b) Prepare and file with the SEC such amendments and post-effective
amendments to each Registration Statement as may be necessary to keep such
Registration Statement continuously effective for the applicable period
specified in Section 2(a); cause the related Prospectus to be supplemented by
any required Prospectus supplement, and as so supplemented to be filed pursuant
to Rule 424 (or any similar provisions then in force) under the Securities Act;
and use its reasonable best efforts to comply with the provisions of the
Securities Act applicable to it with respect to the disposition of all
securities covered by such Registration Statement during the Effectiveness
Period in accordance with the intended methods of disposition by the sellers
thereof set forth in such Registration Statement as so amended or such
Prospectus as so supplemented.

                                       8
<PAGE>
 
       (c) As promptly as practicable give notice to the Notice Holders and the
Initial Purchasers (i) when any Prospectus, Prospectus supplement, Registration
Statement or post-effective amendment to a Registration Statement has been filed
with the SEC and, with respect to a Registration Statement or any post-effective
amendment, when the same has been declared effective, (ii) of any request,
following the effectiveness of the Initial Shelf Registration Statement under
the Securities Act, by the SEC or any other federal or state governmental
authority for amendments or supplements to any Registration Statement or related
Prospectus or for additional information, (iii) of the issuance by the SEC or
any other federal or state governmental authority of any stop order suspending
the effectiveness of any Registration Statement or the initiation or threatening
of any proceedings for that purpose, (iv) of the receipt by the Company of any
notification with respect to the suspension of the qualification or exemption
from qualification of any of the Registrable Securities for sale in any
jurisdiction or the initiation or threatening of any proceeding for such
purpose, (v) of the occurrence of (but not the nature of or details concerning)
a Material Event and (vi) of the determination by the Company that a post-
effective amendment to a Registration Statement will be filed with the SEC,
which notice may, at the discretion of the Company (or as required pursuant to
Section 3(i)), state that it constitutes a Deferral Notice, in which event the
provisions of Section 3(i) shall apply.

       (d) Use commercially reasonable efforts to obtain the withdrawal of any
order suspending the effectiveness of a Registration Statement or the lifting of
any suspension of the qualification (or exemption from qualification) of any of
the Registrable Securities for sale in any jurisdiction in which they have been
qualified for sale, in either case at the earliest possible moment.

       (e) If reasonably requested by the Initial Purchasers or any Notice
Holder, as promptly as practicable incorporate in a Prospectus supplement or
post-effective amendment to a Registration Statement such information as the
Initial Purchasers or such Notice Holder shall, on the basis of an opinion of
nationally-recognized counsel experienced in such matters, determine to be
required to be included therein by applicable law and make any required filings
of such Prospectus supplement or such post-effective amendment; provided, that
the Company shall not be required to take any actions under this Section 3(e)
that are not, in the reasonable opinion of counsel for the Company, in
compliance with applicable law.

       (f) As promptly as practicable furnish to each Notice Holder and the
Initial Purchasers, without charge, at least one (1) conformed copy of the
Registration Statement and any amendment thereto, including financial statements
but excluding schedules, all documents incorporated or deemed to be incorporated
therein by reference and all exhibits (unless requested in writing to the
Company by such Notice Holder or the Initial Purchasers, as the case may be).

       (g) During the Effectiveness Period, deliver to each Notice Holder in
connection with any sale of Registrable Securities pursuant to a Registration
Statement, without charge, as many copies of the Prospectus or Prospectuses
relating to such Registrable Securities (including each

                                       9
<PAGE>
 
preliminary prospectus) and any amendment or supplement thereto as such Notice
Holder may reasonably request; and the Company hereby consents (except during
such periods that a Deferral Notice is outstanding and has not been revoked) to
the use of such Prospectus or each amendment or supplement thereto by each
Notice Holder in connection with any offering and sale of the Registrable
Securities covered by such Prospectus or any amendment or supplement thereto in
the manner set forth therein.

       (h) Prior to any public offering of the Registrable Securities pursuant
to the Shelf Registration Statement, register or qualify or cooperate with the
Notice Holders in connection with the registration or qualification (or
exemption from such registration or qualification) of such Registrable
Securities for offer and sale under the securities or Blue Sky laws of such
jurisdictions within the United States as any Notice Holder reasonably requests
in writing (which request may be included in the Notice and Questionnaire);
prior to any public offering of the Registrable Securities pursuant to the Shelf
Registration Statement, keep each such registration or qualification (or
exemption therefrom) effective during the Effectiveness Period in connection
with such Notice Holder's offer and sale of Registrable Securities pursuant to
such registration or qualification (or exemption therefrom) and do any and all
other acts or things necessary or advisable to enable the disposition in such
jurisdictions of such Registrable Securities in the manner set forth in the
relevant Registration Statement and the related Prospectus; provided, that the
Company will not be required to (i) qualify as a foreign corporation or as a
dealer in securities in any jurisdiction where it would not otherwise be
required to qualify but for this Agreement or (ii) take any action that would
subject it to general service of process in suits or to taxation in any such
jurisdiction where it is not then so subject.

       (i) Upon (A) the issuance by the SEC of a stop order suspending the
effectiveness of the Shelf Registration Statement or the initiation of
proceedings with respect to the Shelf Registration Statement under Section 8(d)
or 8(e) of the Securities Act, (B) the occurrence of any event or the existence
of any fact (a "Material Event") as a result of which any Registration Statement
shall contain any untrue statement of a material fact or omit to state any
material fact required to be stated therein or necessary to make the statements
therein not misleading, or any Prospectus shall contain any untrue statement of
a material fact or omit to state any material fact required to be stated therein
or necessary to make the statements therein, in the light of the circumstances
under which they were made, not misleading, or (C) the occurrence or existence
of any pending corporate development that, in the reasonable discretion of the
Company, makes it appropriate to suspend the availability of the Shelf
Registration Statement and the related Prospectus, (i) in the case of clause (B)
above, subject to the next sentence, as promptly as practicable prepare and
file, if necessary pursuant to applicable law, a post-effective amendment to
such Registration Statement or a supplement to the related Prospectus or any
document incorporated therein by reference or file any other required document
that would be incorporated by reference into such Registration Statement and
Prospectus so that such Registration Statement does not contain any untrue
statement of a material fact or omit to state any material fact required to be
stated therein or necessary to make the statements therein not misleading, and
such Prospectus does not contain any untrue statement of a material fact or omit
to state any material

                                       10
<PAGE>
 
fact required to be stated therein or necessary to make the statements therein,
in the light of the circumstances under which they were made, not misleading, as
thereafter delivered to the purchasers of the Registrable Securities being sold
thereunder, and, in the case of a post-effective amendment to a Registration
Statement, subject to the next sentence, use its best efforts to cause it to be
declared effective as promptly as is practicable, and (ii) give notice to the
Notice Holders that the availability of the Shelf Registration Statement is
suspended (a "Deferral Notice") and, upon receipt of any Deferral Notice, each
Notice Holder agrees not to sell any Registrable Securities pursuant to the
Registration Statement until such Notice Holder's receipt of copies of the
supplemented or amended Prospectus provided for in clause (i) above, or until it
is advised in writing by the Company that the Prospectus may be used, and has
received copies of any additional or supplemental filings that are incorporated
or deemed incorporated by reference in such Prospectus.  The Company will use
reasonable best efforts to ensure that the use of the Prospectus may be resumed
(x) in the case of clause (A) above, as promptly as is practicable, (y) in the
case of clause (B) above, as soon as, in the sole judgment of the Company,
public disclosure of such Material Event would not be prejudicial to or contrary
to the interests of the Company or, if necessary to avoid unreasonable burden or
expense, as soon as practicable thereafter and (z) in the case of clause (C)
above, as soon as, in the discretion of the Company, such suspension is no
longer appropriate.  The Company shall be entitled to exercise its right under
this Section 3(i) to suspend the availability of the Shelf Registration
Statement or any Prospectus, without incurring any obligation to pay liquidated
damages pursuant to Section 2(e), no more than one (1) time in any three (3)
month period or two (2) times in any twelve (12) month period, and the period
during which the availability of the Registration Statement and any Prospectus
is suspended (the "Deferral Period") shall, without incurring any obligation to
pay liquidated damages pursuant to Section 2(e), not exceed thirty (30) days;
provided, that in the case of a Material Event relating to an acquisition or a
probable acquisition or financing, recapitalization, business combination or
other similar transaction, the Company may, without incurring any obligation to
pay liquidated damages pursuant to Section 2(e), deliver to Notice Holders a
second notice to the effect set forth above, which shall have the effect of
extending the Deferral Period by up to an additional thirty (30) days, or such
shorter period of time as is specified in such second notice; provided, that the
aggregate duration of any Deferral Periods shall not, without incurring any
obligation to pay liquidated damages pursuant to Section 2(e), exceed sixty (60)
days in any twelve (12) month period.

       (j) If requested in writing in connection with a disposition of
Registrable Securities pursuant to a Registration Statement, make reasonably
available for inspection during normal business hours by a representative for
the Notice Holders of such Registrable Securities and any broker-dealers,
attorneys and accountants retained by such Notice Holders, all relevant
financial and other records, pertinent corporate documents and properties of the
Company and its subsidiaries, and cause the appropriate officers, directors and
employees of the Company and its subsidiaries to make reasonably available for
inspection during normal business hours all relevant information reasonably
requested by such representative for the Notice Holders or any such broker-
dealers, attorneys or accountants in connection with such disposition, in each
case as is customary for similar "due diligence" examinations; provided,
however, that such persons

                                       11
<PAGE>
 
shall first agree in writing with the Company that any information that is
reasonably and in good faith designated by the Company in writing as
confidential at the time of delivery of such information shall be kept
confidential by such persons and shall be used solely for the purposes of
exercising rights under this Agreement, unless (i) disclosure of such
information is required by court or administrative order or is necessary to
respond to inquiries of regulatory authorities, (ii) disclosure of such
information is required by law (including any disclosure requirements pursuant
to federal securities laws in connection with the filing of any Registration
Statement or the use of any Prospectus referred to in this Agreement), (iii)
such information becomes generally available to the public other than as a
result of a disclosure or failure to safeguard by any such person or (iv) such
information becomes available to any such person from a source other than the
Company and such source is not bound by a confidentiality agreement; and
provided further, that the foregoing inspection and information gathering shall,
to the greatest extent possible, be coordinated on behalf of all the Notice
Holders and the other parties entitled thereto by the counsel referred to in
Section 5.

       (k) Use its reasonable best efforts to comply with all applicable rules
and regulations of the SEC and make generally available to its securityholders
earning statements (which need not be audited) satisfying the provisions of
Section 11(a) of the Securities Act and Rule 158 thereunder (or any similar rule
promulgated under the Securities Act) no later than 45 days after the end of any
3-month period (or 90 days after the end of any 12-month period if such period
is a fiscal year) commencing on the first day of the first fiscal quarter of the
Company commencing after the effective date of a Registration Statement, which
statements shall cover said periods.

       (l) Cooperate with each Notice Holder to facilitate the timely
preparation and delivery of certificates representing Registrable Securities
sold or to be sold pursuant to a Registration Statement, which certificates
shall not bear any restrictive legends, and cause such Registrable Securities to
be in such denominations as are permitted by the Indenture and registered in
such names as such Notice Holder may request in writing at least two (2)
Business Days prior to any sale of such Registrable Securities.

       (m) Provide a CUSIP number for all Registrable Securities covered by each
Registration Statement not later than the effective date of such Registration
Statement and provide the Trustee and the transfer agent for the Common Stock
with printed certificates for the Registrable Securities that are in a form
eligible for deposit with The Depository Trust Company.

       (n) Provide such information as is required for any filings required to
be made with the National Association of Securities Dealers, Inc.

       (o) Upon (i) the filing of the Initial Registration Statement and (ii)
the effectiveness of the Initial Registration Statement, announce the same, in
each case by release to Reuters Economic Services and Bloomberg Business News.

                                       12
<PAGE>
 
        SECTION 4.  Holder's Obligations. Each Holder agrees, by acquisition of
the Registrable Securities, that no Holder of Registrable Securities shall be
entitled to sell any of such Registrable Securities pursuant to a Registration
Statement or to receive a Prospectus relating thereto, unless such Holder has
furnished the Company with a Notice and Questionnaire as required pursuant to
Section 2(d) hereof (including the information required to be included in such
Notice and Questionnaire) and the information set forth in the next sentence.
Each Notice Holder agrees promptly to furnish to the Company all information
required to be disclosed in order to make the information previously furnished
to the Company by such Notice Holder not misleading and any other information
regarding such Notice Holder and the distribution of such Registrable Securities
as the Company may from time to time reasonably request. Any sale of any
Registrable Securities by any Holder shall constitute a representation and
warranty by such Holder that the information relating to such Holder and its
plan of distribution is as set forth in the Prospectus delivered by such Holder
in connection with such disposition, that such Prospectus does not as of the
time of such sale contain any untrue statement of a material fact relating to or
provided by such Holder or its plan of distribution and that such Prospectus
does not as of the time of such sale omit to state any material fact relating to
or provided by such Holder or its plan of distribution necessary to make the
statements in such Prospectus, in the light of the circumstances under which
they were made, not misleading.

        SECTION 5.  Registration Expenses. The Company shall bear all fees and
expenses incurred in connection with the performance by the Company of its
obligations under Sections 2 and 3 of this Agreement whether or not any of the
Registration Statements are declared effective. Such fees and expenses shall
include, without limitation, (i) all registration and filing fees (including,
without limitation, fees and expenses (x) with respect to filings required to be
made with the National Association of Securities Dealers, Inc. and (y) of
compliance with federal and state securities or Blue Sky laws (including,
without limitation, reasonable fees and disbursements of the counsel specified
in the next sentence in connection with Blue Sky qualifications of the
Registrable Securities under the laws of such jurisdictions as the Notice
Holders of a majority of the Registrable Securities being sold pursuant to a
Registration Statement may designate), (ii) printing expenses (including,
without limitation, expenses of printing certificates for Registrable Securities
in a form eligible for deposit with The Depository Trust Company), (iii)
duplication expenses relating to copies of any Registration Statement or
Prospectus delivered to any Holders hereunder, (iv) fees and disbursements of
counsel for the Company in connection with the Shelf Registration Statement, (v)
reasonable fees and disbursements of the Trustee and its counsel and of the
registrar and transfer agent for the Common Stock and (vi) Securities Act
liability insurance obtained by the Company in its sole discretion. In addition,
the Company shall bear or reimburse the Notice Holders for the reasonable fees
and disbursements of one firm of legal counsel for the Holders, which shall
initially be Wilson Sonsini Goodrich & Rosati, Professional Corporation, but
which may, with the written consent of the Initial Purchasers (which shall not
be unreasonably withheld), be another nationally recognized law firm experienced
in securities law matters designated by the Company. In addition, the Company
shall pay the internal expenses of the Company (including, without limitation,
all salaries and expenses of officers and employees performing legal or

                                       13
<PAGE>
 
accounting duties), the expense of any annual audit, the fees and expenses
incurred in connection with the listing of the Registrable Securities on any
securities exchange on which similar securities of the Company are then listed
and the fees and expenses of any person, including special experts, retained by
the Company.  Notwithstanding the provisions of this Section 5, each seller of
Registrable Securities shall pay selling expenses and all registration expenses
to the extent required by applicable law.

        SECTION 6.  Indemnification.

       (a) Indemnification by the Company.  The Company shall indemnify and hold
harmless each Notice Holder and each person, if any, who controls any Notice
Holder (within the meaning of either Section 15 of the Securities Act or Section
20 of the Exchange Act) from and against all losses, liabilities, claims,
damages and expenses (including, without limitation, any legal or other expenses
reasonably incurred in connection with defending or investigating any such
action or claim) (collectively, "Losses"), arising out of or based upon any
untrue statement or alleged untrue statement of a material fact contained in any
Registration Statement or Prospectus or in any amendment or supplement thereto
or in any preliminary prospectus, or arising out of or based upon any omission
or alleged omission to state therein a material fact required to be stated
therein or necessary to make the statements therein not misleading, provided,
however, that the Company shall not be liable in any such case to the extent
that any such Losses arise out of or are based upon an untrue statement or
alleged untrue statement contained in or omission or alleged omission from any
of such documents in reliance upon and conformity with any of the information
relating to such Holder furnished to the Company in writing by such Holder
expressly for use therein; provided further, that the indemnification contained
in this paragraph shall not inure to the benefit of any Holder of Registrable
Securities (or to the benefit of any person controlling such Holder) on account
of any such Losses arising out of or based upon an untrue statement or alleged
untrue statement or omission or alleged omission made in any preliminary
prospectus provided in each case the Company has completed with its several
obligations under Section 3(a) hereof if either (A) (i) such Holder failed to
send or deliver a copy of the Prospectus with or prior to the delivery of
written confirmation of the sale by such Holder to the person asserting the
claim from which such Losses arise and (ii) the Prospectus would have corrected
such untrue statement or alleged untrue statement or such omission or alleged
omission, or (B) (x) such untrue statement or alleged untrue statement, omission
or alleged omission is corrected in an amendment or supplement to the Prospectus
and (y) having previously been furnished by or on behalf of the Company with
copies of the Prospectus as so amended or supplemented, such Holder thereafter
fails to deliver such Prospectus as so amended or supplemented, with or prior to
the delivery of written confirmation of the sale of a Registrable Security to
the person asserting the claim from which such Losses arise.

       (b) Indemnification by Holders of Registrable Securities. Each Holder
agrees severally and not jointly to indemnify and hold harmless the Company and
its respective directors and officers, and each person, if any, who controls the
Company (within the meaning of either Section 15 of the Securities Act or
Section 20 of the Exchange Act), from and against all Losses

                                       14
<PAGE>
 
arising out of or based upon any untrue statement or alleged untrue statement of
a material fact contained in any Registration Statement or Prospectus or in any
amendment or supplement thereto or in any preliminary prospectus, or arising out
of or based upon any omission or alleged omission to state therein a material
fact required to be stated therein or necessary to make the statements therein
not misleading, to the extent, but only to the extent, that such untrue
statement or alleged untrue statement or omission or alleged omission was made
in reliance upon and in conformity with information furnished to the Company by
such Holder expressly for use in such Registration Statement or Prospectus or
amendment or supplement thereto.  In no event shall the liability of any selling
Holder of Registrable Securities hereunder be greater in amount than the dollar
amount of the proceeds received by such Holder upon the sale of the Registrable
Securities pursuant to the Registration Statement giving rise to such
indemnification obligation.

       (c) Conduct of Indemnification Proceedings.  In case any proceeding
(including any governmental investigation) shall be instituted involving any
person in respect of which indemnity may be sought pursuant to either of the two
preceding paragraphs, such person (the "indemnified party") shall promptly
notify the person against whom such indemnity may be sought (the "indemnifying
party") in writing and the indemnifying party, upon request of the indemnified
party, shall retain counsel reasonably satisfactory to the indemnified party to
represent the indemnified party and any others the indemnifying party may
designate in such proceeding and shall pay the reasonable fees and disbursements
of such counsel related to such proceeding.  In any such proceeding, any
indemnified party shall have the right to retain its own counsel, but the fees
and expenses of such counsel shall be at the expense of such indemnified party
unless (i) the indemnifying party and the indemnified party shall have mutually
agreed to the retention of such counsel or (ii) the named parties to any such
proceeding (including any impleaded parties) include both the indemnifying party
and the indemnified party and representation of both parties by the same counsel
would be inappropriate due to actual or potential differing interests between
them.  It is understood that the indemnifying party shall not, in respect of the
legal expenses of any indemnified party in connection with any proceeding or
related proceedings in the same jurisdiction, be liable for the fees and
expenses of more than one separate firm (in addition to any local counsel) for
all indemnified parties, and that all such fees and expenses shall be reimbursed
as they are incurred.  Such separate firm shall be designated in writing by, in
the case of parties indemnified pursuant to Section 6(a), the Holders of a
majority (with Holders of Notes deemed to be the Holders, for purposes of
determining such majority, of the number of shares of Underlying Common Stock
into which such Notes are or would be convertible or exchangeable as of the date
on which such designation is made) of the Registrable Securities covered by the
Registration Statement held by Holders that are indemnified parties pursuant to
Section 6(a) and, in the case of parties indemnified pursuant to Section 6(b),
the Company.  The indemnifying party shall not be liable for any settlement of
any proceeding effected without its written consent, but if settled with such
consent or if there be a final judgment for the plaintiff, the indemnifying
party agrees to indemnify the indemnified party from and against any loss or
liability by reason of such settlement or judgment.  Notwithstanding the
foregoing sentence, if at any time an indemnified party shall have requested an
indemnifying party to reimburse the indemnified party for fees and expenses of
counsel and the indemnified

                                       15
<PAGE>
 
party would be entitled thereto pursuant to the second and third sentences of
this paragraph, the indemnifying party agrees that it shall be liable for any
settlement of any proceeding effected without its written consent if (i) such
settlement is entered into more than 45 days after receipt by such indemnifying
party of the aforesaid request and (ii) such indemnifying party shall not have
reimbursed the indemnified party in accordance with such request prior to the
date of such settlement.  No indemnifying party shall, without the prior written
consent of the indemnified party, effect any settlement of any pending or
threatened proceeding in respect of which any indemnified party is or could have
been a party and indemnity could have been sought hereunder by such indemnified
party, unless such settlement includes an unconditional release of such
indemnified party from all liability on claims that are the subject matter of
such proceeding.

       (d) Contribution.  To the extent that the indemnification provided for in
this Section 6 is unavailable to an indemnified party under Section 6(a) or 6(b)
hereof in respect of any Losses or is insufficient to hold such indemnified
party harmless, then each applicable indemnifying party, in lieu of indemnifying
such indemnified party, shall contribute to the amount paid or payable by such
indemnified party as a result of such Losses (i) in such proportion as is
appropriate to reflect the relative benefits received by the indemnifying party
or parties on the one hand and the indemnified party or parties on the other
hand or (ii) if the allocation provided by clause (i) above is not permitted by
applicable law, in such proportion as is appropriate to reflect not only the
relative benefits referred to in clause (i) above but also the relative fault of
the indemnifying party or parties on the one hand and of the indemnified party
or parties on the other hand in connection with the statements or omissions that
resulted in such Losses, as well as any other relevant equitable considerations.
Benefits received by the Company shall be deemed to be equal to the total net
proceeds from the initial placement pursuant to the Purchase Agreement (before
deducting expenses) of the Registrable Securities to which such Losses relate.
Benefits received by any Holder shall be deemed to be equal to the value of
receiving Registrable Securities that are registered under the Securities Act.
The relative fault of the Holders on the one hand and the Company on the other
hand shall be determined by reference to, among other things, whether the untrue
or alleged untrue statement of a material fact or the omission or alleged
omission to state a material fact relates to information supplied by the Holders
or by the Company, and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such statement or omission.
The Holders' respective obligations to contribute pursuant to this paragraph are
several in proportion to the respective number of Registrable Securities they
have sold pursuant to a Registration Statement, and not joint.

        The parties hereto agree that it would not be just and equitable if
contribution pursuant to this Section 6(d) were determined by pro rata
                                                              --- ----
allocation or by any other method or allocation that does not take into account
the equitable considerations referred to in the immediately preceding paragraph.
The amount paid or payable by an indemnified party as a result of the Losses
referred to in the immediately preceding paragraph shall be deemed to include,
subject to the limitations set forth above, any legal or other expenses
reasonably incurred by such indemnified party in connection with investigating
or defending any such action or claim. Notwithstanding this Section 6(d), an
indemnifying party that is a selling Holder of Registrable Securities shall not
be

                                       16
<PAGE>
 
required to contribute any amount in excess of the amount by which the total
price at which the Registrable Securities sold by such indemnifying party and
distributed to the public were offered to the public exceeds the amount of any
damages that such indemnifying party has otherwise been required to pay by
reason of such untrue or alleged untrue statement or omission or alleged
omission.  No person guilty of fraudulent misrepresentation (within the meaning
of Section 11(f) of the Securities Act) shall be entitled to contribution from
any person who was not guilty of such fraudulent misrepresentation.

       (e) The indemnity, contribution and expense reimbursement obligations of
the parties hereunder shall be in addition to any liability any indemnified
party may otherwise have hereunder, under the Purchase Agreement or otherwise.

       (f) The indemnity and contribution provisions contained in this Section 6
shall remain operative and in full force and effect regardless of (i) any
termination of this Agreement, (ii) any investigation made by or on behalf of
any Holder or any person controlling any Holder, or the Company, or the
Company's officers or directors or any person controlling the Company and (iii)
the sale of any Registrable Securities by any Holder.

        SECTION 7.  Information Requirements.  (a) The Company covenants that,
if at any time before the end of the Effectiveness Period the Company is not
subject to the reporting requirements of the Exchange Act, it will cooperate
with any Holder of Registrable Securities and take such further reasonable
action as any Holder of Registrable Securities may reasonably request in writing
(including, without limitation, making such reasonable representations as any
such Holder may reasonably request), all to the extent required from time to
time to enable such Holder to sell Registrable Securities without registration
under the Securities Act within the limitation of the exemptions provided by
Rule 144 and Rule 144A under the Securities Act and customarily taken in
connection with sales pursuant to such exemptions. Upon the written request of
any Holder of Registrable Securities, the Company shall deliver to such Holder a
written statement as to whether it has complied with such filing requirements,
unless such a statement has been included in the Company's most recent report
required to be filed and filed pursuant to Section 13 or Section 15(d) of
Exchange Act. Notwithstanding the foregoing, nothing in this Section 7 shall be
deemed to require the Company to register any of its securities (other than the
Common Stock) under any section of the Exchange Act.

        SECTION 8.  Miscellaneous.

       (a) No Conflicting Agreements. The Company is not, as of the date hereof,
a party to, nor shall it, on or after the date of this Agreement, enter into,
any agreement with respect to its securities that conflicts with the rights
granted to the Holders of Registrable Securities in this Agreement. The Company
represents and warrants that the rights granted to the Holders of Registrable
Securities hereunder do not in any way conflict with the rights granted to the
holders of the Company's securities under any other agreements.

                                       17
<PAGE>
 
       (b) Amendments and Waivers. The provisions of this Agreement, including
the provisions of this sentence, may not be amended, modified or supplemented,
and waivers or consents to departures from the provisions hereof may not be
given, unless the Company has obtained the written consent of Holders of a
majority of the then outstanding Underlying Common Stock constituting
Registrable Securities (with Holders of Notes deemed to be the Holders, for
purposes of this Section, of the number of outstanding shares of Underlying
Common Stock into which such Notes are or would be convertible or exchangeable
as of the date on which such consent is requested). Notwithstanding the
foregoing, a waiver or consent to depart from the provisions hereof with respect
to a matter that relates exclusively to the rights of Holders of Registrable
Securities whose securities are being sold pursuant to a Registration Statement
and that does not directly or indirectly affect the rights of other Holders of
Registrable Securities may be given by Holders of at least a majority of the
Registrable Securities being sold by such Holders pursuant to such Registration
Statement; provided, that the provisions of this sentence may not be amended,
modified, or supplemented except in accordance with the provisions of the
immediately preceding sentence. Each Holder of Registrable Securities
outstanding at the time of any such amendment, modification, supplement, waiver
or consent or thereafter shall be bound by any such amendment, modification,
supplement, waiver or consent effected pursuant to this Section 8(b), whether or
not any notice, writing or marking indicating such amendment, modification,
supplement, waiver or consent appears on the Registrable Securities or is
delivered to such Holder.

       (c) Notices. All notices and other communications provided for or
permitted hereunder shall be made in writing by hand delivery, by telecopier, by
courier guaranteeing overnight delivery or by first-class mail, return receipt
requested, and shall be deemed given (i) when made, if made by hand delivery,
(ii) upon confirmation, if made by telecopier, (iii) one (1) Business Day after
being deposited with such courier, if made by overnight courier or (iv) on the
date indicated on the notice of receipt, if made by first-class mail, to the
parties as follows:

          (w) if to a Holder of Registrable Securities, at the most current
          address given by such Holder to the Company in a Notice and
          Questionnaire or any amendment thereto;

          (x) if to the Company, to:

                  Aviron
                  297 North Bernardo Avenue
                  Mountain View, CA  94043
                  Attention:  Fred Kurland
                  Telecopy No.: (650) 919-2410

                  and

                                       18
<PAGE>
 
                  Cooley Godward LLP
                  Five Palo Alto Square
                  3000 El Camion Real
                  Palo Alto, CA  94306-2155
                  Attn: Alan C. Mendelson, Esq.
                  Telecopy No.:  (650) 857-0663



          (y) if to the Initial Purchasers, to:

                  Morgan Stanley & Co. Incorporated
                  1585 Broadway
                  New York, New York
                  Attention:  Equity Capital Markets
                  Telecopy No.: (212) 761-0356

                  and

                  Wilson Sonsini Goodrich & Rosati
                  Professional Corporation
                  650 Page Mill Road
                  Palo Alto, CA  94304-1050
                  Attention:  David J. Segre, Esq.
                  Telecopy No. (650) 493-6811

or to such other address as such person may have furnished to the other persons
identified in this Section 8(c) in writing in accordance herewith.

          (d)  Approval of Holders. Whenever the consent or approval of Holders
of a specified percentage of Registrable Securities is required hereunder,
Registrable Securities held by the Company or its affiliates (as such term is
defined in Rule 405 under the Securities Act) (other than the Initial Purchasers
or subsequent Holders of Registrable Securities if such subsequent Holders are
deemed to be such affiliates solely by reason of their holdings of such
Registrable Securities) shall not be counted in determining whether such consent
or approval was given by the Holders of such required percentage.

          (e) Successors and Assigns.  Any person who purchases any Registrable
Securities from the Initial Purchasers shall be deemed, for purposes of this
Agreement, to be an assignee of the Initial Purchasers.  This Agreement shall
inure to the benefit of and be binding upon the successors and assigns of each
of the parties and shall inure to the benefit of and be binding upon each Holder
of any Registrable Securities.

                                       19
<PAGE>
 
          (f) Counterparts.  This Agreement may be executed in any number of
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be original and all of which taken together
shall constitute one and the same agreement.

          (g) Headings.  The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

          (h) Governing Law. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED
IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT REGARD TO
CONFLICTS OF LAWS PRINCIPLES THEREOF.

          (i) Severability. If any term, provision, covenant or restriction of
this Agreement is held to be invalid, illegal, void or unenforceable, the
remainder of the terms, provisions, covenants and restrictions set forth herein
shall remain in full force and effect and shall in no way be affected, impaired
or invalidated thereby, and the parties hereto shall use their best efforts to
find and employ an alternative means to achieve the same or substantially the
same result as that contemplated by such term, provision, covenant or
restriction, it being intended that all of the rights and privileges of the
parties shall be enforceable to the fullest extent permitted by law.

          (j) Entire Agreement.  This Agreement is intended by the parties as a
final expression of their agreement and is intended to be a complete and
exclusive statement of the agreement and understanding of the parties hereto in
respect of the subject matter contained herein and the registration rights
granted by the Company with respect to the Registrable Securities.  Except as
provided in the Purchase Agreement, there are no restrictions, promises,
warranties or undertakings, other than those set forth or referred to herein,
with respect to the registration rights granted by the Company with respect to
the Registrable Securities.  This Agreement supersedes all prior agreements and
undertakings among the parties with respect to such registration rights.  No
party hereto shall have any rights, duties or obligations other than those
specifically set forth in this Agreement.  Without limiting the generality of
the foregoing, the Company shall have no obligation to participate in "road
show" or, except as specifically provided in this Agreement, "due diligence"
activities in connection with any underwritten public offering of Registrable
Securities, and the Company shall have no obligation to enter into underwriting
or indemnification agreements with respect to, or deliver opinions, comfort
letters or closing certificates in connection with, any such underwritten public
offering.

          (k) Termination.  This Agreement and the obligations of the parties
hereunder shall terminate upon the end of the Effectiveness Period, except for
any liabilities or obligations under Sections 4, 5 or 6 hereof and the
obligations to make payments of and provide for liquidated damages under Section
2(e) hereof to the extent such damages accrue prior to the end of the
Effectiveness Period, each of which shall remain in effect in accordance with
its terms.

                                       20
<PAGE>
 
       IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first written above.


                            AVIRON


                                   /s/ J. Leighton Read, M.D.      
                            By:  _______________________________________________
                                   Name:   J. Leighton Read, M.D.      
                                   Title:  Chief Executive Officer      


Accepted as of the date first
above written:



MORGAN STANLEY & CO. INCORPORATED
BEAR, STEARNS & CO. INC.
CREDIT SUISSE FIRST BOSTON CORPORATION
HAMBRECHT & QUIST LLC
(for the benefit of themselves and for the benefit of the Holders)


By:  MORGAN STANLEY & CO. INCORPORATED


       /s/ Catherine J. Friedman      
By:  ____________________________________________________________
       Name:   Catherine J. Friedman      
       Title:  Managing Director      

                                       21

<PAGE>
                                                                    EXHIBIT 4.12


 
                                    AVIRON

                                      TO

                              MARINE MIDLAND BANK
                                    TRUSTEE



                                   INDENTURE



                          DATED AS OF MARCH 15, 1998

                5 3/4% CONVERTIBLE SUBORDINATED NOTES DUE 2005
<PAGE>
 
                                    AVIRON

     Reconciliation and Tie Between the Trust Indenture Act of 1939 and
Indenture, dated as of March 15, 1998, between Aviron and Marine Midland Bank,
as Trustee.
<TABLE>
<CAPTION>
TRUST INDENTURE ACT SECTION       INDENTURE SECTION
<S>                            <C>
(S) 310(a)(1)................                   8.9
(a)(2).......................                   8.9
(a)(3).......................        Not Applicable
(a)(4).......................        Not Applicable
(a)(5).......................                   8.9
(b)..........................  8.8; 8.9; 8.10; 8.11
(S) 311(a)...................                  8.13
(b)..........................                  8.13
(b)(2).......................                   6.3(a)
(S) 312(a)...................              6.1; 6.2(a)
(b)..........................                   6.2(b)
(c)..........................                   6.2(c)
(S) 313(a)...................                   6.3(a)
(b)..........................                   6.3(a)
(c)..........................                   6.3(a)
(d)..........................                   6.3(b)
(S) 314(a)...................                  6.14
(b)..........................        Not Applicable
(c)(1).......................                  16.5
(c)(2).......................                  16.5
(c)(3).......................        Not Applicable
(d)..........................        Not Applicable
(e)..........................                  16.5
(S) 315(a)...................                   8.1
(b)..........................                   7.8
(c)..........................                   8.1
(d)..........................                   8.1
(d)(1).......................                   8.1(a)
(d)(2).......................                   8.1(b)
(d)(3).......................                   8.1(c)
(e)..........................                   7.9
(S) 316(a)...................                   7.7
(a)(1)(A)....................                   7.7
(a)(1)(B)....................                   7.7
(a)(2).......................        Not Applicable
(b)..........................                   7.4
(S) 317(a)(1)................                   7.5
(a)(2).......................                   7.5
(b)..........................                   5.4
(S) 318(a)...................                  16.7
 
</TABLE>
___________________
Note:  This reconciliation and tie shall not, for any purpose, be deemed to be a
       part of the Indenture.


                                      -i-
<PAGE>
 
                               TABLE OF CONTENTS

                                                                       PAGE

ARTICLE I  DEFINITIONS...............................................   -1-

     Section 1.1  Definitions........................................   -1-
          Affiliate..................................................   -2-
          Board of Directors.........................................   -2-
          Business Day...............................................   -2-
          Closing Price..............................................   -2-
          Commission.................................................   -2-
          Common Stock...............................................   -2-
          Company....................................................   -2-
          Conversion Price...........................................   -3-
          Corporate Trust Office.....................................   -3-
          Custodian..................................................   -3-
          Default....................................................   -3-
          Depositary.................................................   -3-
          Designated Senior Indebtedness.............................   -3-
          Exchange Act...............................................   -3-
          Event of Default...........................................   -3-
          Fundamental Change.........................................   -3-
          Global Note................................................   -4-
          Indebtedness...............................................   -4-
          Indenture..................................................   -4-
          Initial Purchasers.........................................   -4-
          Institutional Accredited Investor..........................   -5-
          Liquidated Damages Amount..................................   -5-
          Note or Notes..............................................   -5-
          Noteholder or holder.......................................   -5-
          Note register..............................................   -5-
          Officers' Certificate......................................   -5-
          Opinion of Counsel.........................................   -5-
          outstanding................................................   -5-
          Payment Blockage Notice....................................   -6-
          Person.....................................................   -6-
          Portal Market..............................................   -6-
          Predecessor Note...........................................   -6-
          QIB........................................................   -6-
          Registration Rights Agreement..............................   -6-
          Representative.............................................   -6-
          Responsible Officer........................................   -6-
          Restricted Securities......................................   -6-
          Rule 144A..................................................   -6-

                                      -i-
<PAGE>

<TABLE>    
<CAPTION> 
<S>      <C>                                                          <C>
 
          Securities Act.............................................   -7-
          Senior Indebtedness........................................   -7-
          Significant Subsidiary.....................................   -7-
          Subsidiary.................................................   -7-
          Trading Day................................................   -7-
          Trigger Event..............................................   -7-
          Trust Indenture Act........................................   -7-
          Trustee....................................................   -8-

ARTICLE II  ISSUE, DESCRIPTION, EXECUTION,
            REGISTRATION AND EXCHANGE OF NOTES.......................   -8-

     Section 2.1    Designation Amount and Issue of Notes............   -8-
     Section 2.2    Form of Notes....................................   -8-
     Section 2.3    Date and Denomination of Notes; Payments of
                    Interest.........................................   -9-
     Section 2.4    Execution of Notes...............................  -10-
     Section 2.5    Exchange and Registration of Transfer of Notes:
                    Restrictions on Transfer; Depositary.............  -11-
     Section 2.6    Mutilated, Destroyed, Lost or Stolen Notes.......  -17-
     Section 2.7    Temporary Notes..................................  -18-
     Section 2.8    Cancellation of Notes Paid, Etc..................  -19-
     Section 2.9    CUSIP Numbers....................................  -19-

Article III  Redemption Of Notes.....................................  -19-

     Section 3.1    Redemption Prices................................  -19-
     Section 3.2    Notice of Redemption; Selection of Notes.........  -19-
     Section 3.3    Payment of Notes Called for Redemption...........  -21-
     Section 3.4    Conversion Arrangement on Call for Redemption....  -21-
     Section 3.5    Redemption at Option of Holders..................  -22-

Article IV  Subordination Of Notes...................................  -24-

     Section 4.1    Agreement of Subordination.......................  -24-
     Section 4.2    Payments to Noteholders..........................  -24-
     Section 4.3    Subrogation of Notes.............................  -27-
     Section 4.4    Authorization to Effect Subordination............  -28-
     Section 4.5    Notice to Trustee................................  -28-
     Section 4.6    Trustee's Relation to Senior Indebtedness........  -29-
     Section 4.7    No Impairment of Subordination...................  -29-
     Section 4.8    Certain Conversions Not Deemed Payment...........  -29-
     Section 4.9    Article Applicable to Paying Agents..............  -30-
     Section 4.10   Senior Indebtedness Entitled to Rely.............  -30-
     Section 4.11   Reliance on Judicial Order or Certificate of
                    Liquidating Agent................................  -30-

</TABLE>      

                                      ii
<PAGE>

<TABLE>    
<CAPTION> 
<S>                <C>                                                <C>
 
ARTICLE V  PARTICULAR COVENANTS OF THE COMPANY.......................  -30-

     Section 5.1    Payment of Principal, Premium and Interest.......  -30-
     Section 5.2    Maintenance of Office or Agency..................  -30-
     Section 5.3    Appointments to Fill Vacancies in Trustee's 
                    Office...........................................  -31-
     Section 5.4    Provisions as to Paying Agent....................  -31-
     Section 5.5    Existence........................................  -32-
     Section 5.6    Maintenance of Properties........................  -32-
     Section 5.7    Payment of Taxes and Other Claims................  -33-
     Section 5.8    Rule 144A Information Requirement................  -33-
     Section 5.9    Stay, Extension and Usury Laws...................  -33-
     Section 5.10   Compliance Certificate...........................  -34-

ARTICLE VI  NOTEHOLDERS' LISTS AND REPORTS BY THE
 COMPANY AND THE TRUSTEE.............................................  -34-

     Section 6.1    Noteholders' Lists...............................  -34-
     Section 6.2    Preservation and Disclosure of Lists.............  -34-
     Section 6.3    Reports by Trustee...............................  -35-
     Section 6.4    Reports by Company...............................  -35-

ARTICLE VII  REMEDIES OF THE TRUSTEE AND NOTEHOLDERS ON
 AN EVENT OF DEFAULT.................................................  -35-

     Section 7.1    Events of Default................................  -35-
     Section 7.2    Payments of Notes on Default; Suit Therefor......  -37-
     Section 7.3    Application of Monies Collected by Trustee.......  -39-
     Section 7.4    Proceedings by Noteholder........................  -39-
     Section 7.5    Proceedings by Trustee...........................  -40-
     Section 7.6    Remedies Cumulative and Continuing...............  -40-
     Section 7.7    Direction of Proceedings and Waiver of Defaults by
                    Majority of Noteholders..........................  -41-
     Section 7.8    Notice of Defaults...............................  -41-
     Section 7.9    Undertaking to Pay Costs.........................  -41-

ARTICLE VIII  CONCERNING THE TRUSTEE.................................  -42-

     Section 8.1    Duties and Responsibilities of Trustee...........  -42-
     Section 8.2    Reliance on Documents, Opinions, Etc.............  -43-
     Section 8.3    No Responsibility for Recitals, Etc..............  -44-
     Section 8.4    Trustee, Paying Agents, Conversion Agents or
                    Registrar May Own Notes..........................  -44-
     Section 8.5    Monies to Be Held in Trust.......................  -44-
     Section 8.6    Compensation and Expenses of Trustee.............  -44-
     Section 8.7    Officers' Certificate as Evidence................  -45-
     Section 8.8    Conflicting Interests of Trustee.................  -45-
     Section 8.9    Eligibility of Trustee...........................  -45-

</TABLE>      

                                    -iii-
<PAGE>
<TABLE>     
<CAPTION> 
<S>                 <C>                                               <C>
 
     Section 8.10   Resignation or Removal of Trustee................  -46-
     Section 8.11   Acceptance by Successor Trustee..................  -47-
     Section 8.12   Succession by Merger, Etc........................  -47-
     Section 8.13   Preferential Collection of Claims................  -48-
     Section 8.14   Trustee's Application for Instructions from the
                    Company..........................................  -48-

ARTICLE IX  CONCERNING THE NOTEHOLDERS...............................  -48-

     Section 9.1    Action by Noteholders............................  -48-
     Section 9.2    Proof of Execution by Noteholders................  -49-
     Section 9.3    Who Are Deemed Absolute Owners...................  -49-
     Section 9.4    Company-Owned Notes Disregarded..................  -49-
     Section 9.5    Revocation of Consents; Future Holders Bound.....  -50-

ARTICLE X  NOTEHOLDERS' MEETINGS.....................................  -50-

     Section 10.1   Purpose of Meetings..............................  -50-
     Section 10.2   Call of Meetings by Trustee......................  -50-
     Section 10.3   Call of Meetings by Company or Noteholders.......  -51-
     Section 10.4   Qualifications for Voting........................  -51-
     Section 10.5   Regulations......................................  -51-
     Section 10.6   Voting...........................................  -52-
     Section 10.7   No Delay of Rights by Meeting....................  -52-

ARTICLE XI  SUPPLEMENTAL INDENTURES..................................  -52-

     Section 11.1   Supplemental Indentures Without Consent of
                    Noteholders......................................  -52-
     Section 11.2   Supplemental Indentures with Consent of
                    Noteholders......................................  -54-
     Section 11.3   Effect of Supplemental Indenture.................  -54-
     Section 11.4   Notation on Notes................................  -55-
     Section 11.5   Evidence of Compliance of Supplemental Indenture
                    to Be Furnished Trustee..........................  -55-

ARTICLE XII  CONSOLIDATION, MERGER, SALE, CONVEYANCE AND LEASE.......  -55-

     Section 12.1   Company May Consolidate Etc. on Certain Terms....  -55-
     Section 12.2   Successor Corporation to Be Substituted..........  -56-
     Section 12.3   Opinion of Counsel to Be Given Trustee...........  -56-

ARTICLE XIII  SATISFACTION AND DISCHARGE OF INDENTURE................  -56-

     Section 13.1   Discharge of Indenture...........................  -56-
     Section 13.2   Deposited Monies to Be Held in Trust by Trustee..  -57-
     Section 13.3   Paying Agent to Repay Monies Held................  -57-
</TABLE>      

                                     -iv-
<PAGE>

<TABLE>     
<CAPTION> 
<S>                <C>                                                <C>
 
     Section 13.4   Return of Unclaimed Monies.......................  -57-
     Section 13.5   Reinstatement....................................  -57-

ARTICLE XIV  IMMUNITY OF INCORPORATORS, STOCKHOLDERS,
             OFFICERS AND DIRECTORS..................................  -58-

     Section 14.1   Indenture and Notes Solely Corporate Obligations.  -58-

ARTICLE XV  CONVERSION OF NOTES......................................  -58-

     Section 15.1   Right to Convert.................................  -58-
     Section 15.2   Exercise of Conversion Privilege; Issuance of
                    Common Stock on Conversion; No Adjustment for
                    Interest or Dividends............................  -59-
     Section 15.3   Cash Payments in Lieu of Fractional Shares.......  -60-
     Section 15.4   Conversion Price.................................  -60-
     Section 15.5   Adjustment of Conversion Price...................  -60-
     Section 15.6   Effect of Reclassification, Consolidation, Merger
                    or Sale..........................................  -68-
     Section 15.7   Taxes on Shares Issued...........................  -69-
     Section 15.8   Reservation of Shares; Shares to Be Fully Paid;
                    Compliance with Governmental Requirements; 
                    Listing of Common Stock..........................  -70-
     Section 15.9   Responsibility of Trustee........................  -70-
     Section 15.10  Notice to Holders Prior to Certain Actions.......  -71-

ARTICLE XVI  MISCELLANEOUS PROVISIONS................................  -72-

     Section 16.1   Provisions Binding on Company's Successors.......  -72-
     Section 16.2   Official Acts by Successor Corporation...........  -72-
     Section 16.3   Addresses for Notices, Etc.......................  -72-
     Section 16.4   Governing Law....................................  -72-
     Section 16.5   Evidence of Compliance with Conditions Precedent;
                    Certificates to Trustee..........................  -72-
     Section 16.6   Legal Holidays...................................  -73-
     Section 16.7   Trust Indenture Act..............................  -73-
     Section 16.8   No Security Interest Created.....................  -73-
     Section 16.9   Benefits of Indenture............................  -73-
     Section 16.10  Table of Contents, Headings, Etc.................  -74-
     Section 16.11  Authenticating Agent.............................  -74-
     Section 16.12  Execution in Counterparts........................  -75-
</TABLE>      

                                      -v-
 
<PAGE>
 
                                   INDENTURE

     INDENTURE, dated as of March 15, 1998, between Aviron, a Delaware
corporation (hereinafter sometimes called the "Company", as more fully set forth
in Section 1.1), and Marine Midland Bank, a New York banking corporation and
trust company, as trustee hereunder (hereinafter sometimes called the "Trustee",
as more fully set forth in Section 1.1).

                                  WITNESSETH:

     WHEREAS, for its lawful corporate purposes, the Company has duly authorized
the issue of its 5 3/4% Convertible Subordinated Notes due 2005 (hereinafter
sometimes called the "Notes"), in an aggregate principal amount not to exceed
$115,000,000 and, to provide the terms and conditions upon which the Notes are
to be authenticated, issued and delivered, the Company has duly authorized the
execution and delivery of this Indenture; and

     WHEREAS, the Notes, the certificate of authentication to be borne by the
Notes, a form of assignment, a form of option to elect repayment upon a
Fundamental Change, and a form of conversion notice to be borne by the Notes are
to be substantially in the forms hereinafter provided for; and

     WHEREAS, all acts and things necessary to make the Notes, when executed by
the Company and authenticated and delivered by the Trustee or a duly authorized
authenticating agent, as in this Indenture provided, the valid, binding and
legal obligations of the Company, and to constitute these presents a valid
agreement according to its terms, have been done and performed, and the
execution of this Indenture and the issue hereunder of the Notes have in all
respects been duly authorized.

     NOW, THEREFORE, THIS INDENTURE WITNESSETH:

     That in order to declare the terms and conditions upon which the Notes are,
and are to be, authenticated, issued and delivered, and in consideration of the
premises and of the purchase and acceptance of the Notes by the holders thereof,
the Company covenants and agrees with the Trustee for the equal and
proportionate benefit of the respective holders from time to time of the Notes
(except as otherwise provided below), as follows:


                                   ARTICLE I

                                  DEFINITIONS

     SECTION 1.1   DEFINITIONS.  The terms defined in this Section 1.1 (except
as herein otherwise expressly provided or unless the context otherwise requires)
for all purposes of this Indenture and of any indenture supplemental hereto
shall have the respective meanings specified in this Section 1.1.  All other
terms used in this Indenture that are defined in the Trust Indenture Act or
which are by reference therein defined in the Securities Act (except as herein
otherwise expressly provided or unless the context otherwise requires) shall
have the meanings assigned to such terms in said Trust Indenture Act and in
<PAGE>
 
said Securities Act as in force at the date of the execution of this Indenture.
The words "herein," "hereof," "hereunder," and words of similar import refer to
this Indenture as a whole and not to any particular Article, Section or other
Subdivision.  The terms defined in this Article include the plural as well as
the singular.

          AFFILIATE:  The term "Affiliate" of any specified Person shall mean
any other Person directly or indirectly controlling or controlled by or under
direct or indirect common control with such specified Person.  For the purposes
of this definition, "control," when used with respect to any specified Person
means the power to direct or cause the direction of the management and policies
of such Person, directly or indirectly, whether through the ownership of voting
securities, by contract or otherwise; and the terms "controlling" and
"controlled" have meanings correlative to the foregoing.

          BOARD OF DIRECTORS:  The term "Board of Directors" shall mean the
Board of Directors of the Company or a committee of such Board duly authorized
to act for it hereunder.

          BUSINESS DAY:  The term "Business Day" shall mean each Monday,
Tuesday, Wednesday, Thursday and Friday which is not a day on which the banking
institutions in The City of New York or the city in which the Corporate Trust
Office is located are authorized or obligated by law or executive order to close
or be closed.

          CLOSING PRICE: The term "Closing Price" shall have the meaning
specified in Section 15.5(h)(1).

          COMMISSION: The term "Commission" shall mean the Securities and
Exchange Commission.

          COMMON STOCK:  The term "Common Stock" shall mean any stock of any
class of the Company which has no preference in respect of dividends or of
amounts payable in the event of any voluntary or involuntary liquidation,
dissolution or winding up of the Company and which is not subject to redemption
by the Company.  Subject to the provisions of Section 15.6, however, shares
issuable on conversion of Notes shall include only shares of the class
designated as common stock of the Company at the date of this Indenture or
shares of any class or classes resulting from any reclassification or
reclassifications thereof and which have no preference in respect of dividends
or of amounts payable in the event of any voluntary or involuntary liquidation,
dissolution or winding up of the Company and which are not subject to redemption
by the Company; provided that if at any time there shall be more than one such
resulting class, the shares of each such class then so issuable shall be
substantially in the proportion which the total number of shares of such class
resulting from all such reclassifications bears to the total number of shares of
all such classes resulting from all such reclassifications.

          COMPANY:  The term "Company" shall mean Aviron, a Delaware
corporation, having its principal office at 297 North Bernardo Avenue, Mountain
View, California 94043 and subject to the provisions of Article XII, shall
include its successors and assigns.

                                      -2-
<PAGE>
 
          CONVERSION PRICE: The term "Conversion Price" shall have the meaning
specified in Section 15.4.

          CORPORATE TRUST OFFICE:  The term "Corporate Trust Office" or other
similar term, shall mean the principal office of the Trustee at which at any
particular time its corporate trust business shall be principally administered,
which office is, at the date as of which this Indenture is dated, located at 140
Broadway, 12th Floor, New York, New York 10005, Attention:  Corporate Trust
Department (Aviron -5 3/4% Convertible Subordinated Notes due 2005).

          CUSTODIAN:  The term "Custodian" shall mean Marine Midland Bank, as
custodian with respect to the Notes in global form, or any successor entity
thereto.

          DEFAULT:  The term "default" shall mean any event that is, or after
notice or passage of time, or both, would be, an Event of Default.

          DEPOSITARY:  The term "Depositary" shall mean, with respect to the
Notes issuable or issued in whole or in part in global form, the Person
specified in Section 2.5(d) as the Depositary with respect to such Notes, until
a successor shall have been appointed and become such pursuant to the applicable
provisions of this Indenture, and thereafter, "Depositary" shall mean or include
such successor.

          DESIGNATED SENIOR INDEBTEDNESS:  The term "Designated Senior
Indebtedness" shall mean any Senior Indebtedness in which the instrument
creating or evidencing the same or the assumption or guarantee thereof (or
related agreements or documents to which the Company is a party) expressly
provides that such Senior Indebtedness shall be "Designated Senior Indebtedness"
for purposes of this Indenture (provided that such instrument, agreement or
other document may place limitations and conditions on the right of such Senior
Indebtedness to exercise the rights of Designated Senior Indebtedness).  If any
payment made to any holder of any Designated Senior Indebtedness or its
Representative with respect to such Designated Senior Indebtedness is rescinded
or must otherwise be returned by such holder or Representative upon the
insolvency, bankruptcy or reorganization of the Company or otherwise, the
reinstated Indebtedness of the Company arising as a result of such rescission or
return shall constitute Designated Senior Indebtedness effective as of the date
of such rescission or return.

          EXCHANGE ACT:  The term "Exchange Act" shall mean the Securities
Exchange Act of 1934, as amended, and the rules and regulations promulgated
thereunder, as in effect from time to time.

          EVENT OF DEFAULT: The term "Event of Default" shall mean any event
specified in Section 7.1(a), (b), (c), (d) or (e).

          FUNDAMENTAL CHANGE:  The term "Fundamental Change" shall mean the
occurrence of any transaction or event in connection with which all or
substantially all of the Common Stock shall be exchanged for, converted into,
acquired for or constitute solely the right to receive consideration (whether by
means of an exchange offer, liquidation, tender offer, consolidation, merger,
combination,

                                      -3-
<PAGE>
 
reclassification, recapitalization or otherwise) which is not all or
substantially all common stock listed (or, upon consummation of or immediately
following such transaction or event, will be listed) on a United States national
securities exchange or approved for quotation on the Nasdaq National Market or
any similar United States system of automated dissemination of quotations of
securities prices.

          GLOBAL NOTE: The term "Global Note" shall have the meaning set forth
in Section 2.5(b).

          INDEBTEDNESS:  The term "Indebtedness" shall mean, with respect to any
Person, and without duplication, (a) all indebtedness, obligations and other
liabilities (contingent or otherwise) of such Person for borrowed money
(including obligations of the Company in respect of overdrafts, foreign exchange
contracts, currency exchange agreements, interest rate protection agreements,
and any loans or advances from banks, whether or not evidenced by notes or
similar instruments, and all commitment, standby and other fees due and payable
to financial institutions with respect to credit facilities available to such
Person) or evidenced by bonds, debentures, notes or similar instruments (whether
or not the recourse of the lender is to the whole of the assets of such Person
or to only a portion thereof), other than any account payable or other accrued
current liability or obligation incurred in the ordinary course of business in
connection with the obtaining of materials or services; (b) all reimbursement
obligations and other liabilities (contingent or otherwise) of such Person with
respect to letters of credit, bank guarantees or bankers' acceptances; (c) all
obligations and liabilities (contingent or otherwise) in respect of leases of
real or personal property or other assets of such Person required, in conformity
with generally accepted accounting principles, to be accounted for as
capitalized lease obligations on the balance sheet of such Person and all
obligations and other liabilities (contingent or otherwise) under any lease or
related document (including a purchase agreement) in connection with the lease
of real property which provides that such Person is contractually obligated to
purchase or cause a third party to purchase the leased property and thereby
guarantee a minimum residual value of the leased property to the lessor and the
obligations of such Person under such lease or related document to purchase or
to cause a third party to purchase such leased property; (d) all obligations of
such Person (contingent or otherwise) with respect to an interest rate or other
swap, cap or collar agreement or other similar instrument or agreement or
foreign currency hedge, exchange, purchase or similar instrument or agreement;
(e) all direct or indirect guaranties or similar agreements by such Person in
respect of, and obligations or liabilities (contingent or otherwise) of such
Person to purchase or otherwise acquire or otherwise assure a creditor against
loss in respect of, indebtedness, obligations or liabilities of another Person
of the kind described in clauses (a) through (d); (f) any indebtedness or other
obligations described in clauses (a) through (e) secured by any mortgage,
pledge, lien or other encumbrance existing on property which is owned or held by
such Person, regardless of whether the indebtedness or other obligation secured
thereby shall have been assumed by such Person; and (g) any and all deferrals,
renewals, extensions and refundings of, or amendments, modifications or
supplements to, any indebtedness, obligation or liability of the kind described
in clauses (a) through (f).

          INDENTURE:  The term "Indenture" shall mean this instrument as
originally executed or, if amended or supplemented as herein provided, as so
amended or supplemented.

          INITIAL PURCHASERS:  The term "Initial Purchasers" shall mean Morgan
Stanley & Co. Incorporated, Bear, Stearns & Co. Inc., Credit Suisse First Boston
and Hambrecht & Quist.

                                      -4-
<PAGE>
 
          INSTITUTIONAL ACCREDITED INVESTOR:  The term "Institutional Accredited
Investor" shall mean an institutional "accredited investor" within the meaning
of Rule 501(a)(1), (2), (3) or (7) under the Securities Act.

          LIQUIDATED DAMAGES AMOUNT:  The term "Liquidated Damages Amount" shall
have the meaning specified in Section 2(e) of the Registration Rights Agreement.

          NOTE OR NOTES: The terms "Note" or "Notes" shall mean any Note or
Notes, as the case may be, authenticated and delivered under this Indenture,
including the Global Note.

          NOTEHOLDER OR HOLDER:  The terms "Noteholder" or "holder" as applied
to any Note, or other similar terms (but excluding the term "beneficial
holder"), shall mean any Person in whose name at the time a particular Note is
registered on the Note registrar's books.

          NOTE REGISTER: The term "Note register" shall have the meaning
specified in Section 2.5.

          OFFICERS' CERTIFICATE:  The term "Officers' Certificate," when used
with respect to the Company, shall mean a certificate signed by both (a) the
President, the Chief Executive Officer, Executive or Senior Vice President or
any Vice President (whether or not designated by a number or numbers or word or
words added before or after the title "Vice President") and (b) by the Treasurer
or any Assistant Treasurer or Secretary or any Assistant Secretary of the
Company.

          OPINION OF COUNSEL:  The term "Opinion of Counsel" shall mean an
opinion in writing signed by legal counsel, who may be an employee of or counsel
to the Company, or other counsel acceptable to the Trustee.

          OUTSTANDING:  The term "outstanding," when used with reference to
Notes, shall, subject to the provisions of Section 9.4, mean, as of any
particular time, all Notes authenticated and delivered by the Trustee under this
Indenture, except

                (a) Notes theretofore canceled by the Trustee or delivered to
the Trustee for cancellation;

                (b) Notes, or portions thereof, (i) for the redemption of which
monies in the necessary amount shall have been deposited in trust with the
Trustee or with any paying agent (other than the Company) or (ii) which shall
have been otherwise defeased in accordance with Article XIII;

                (c) Notes in lieu of which, or in substitution for which, other
Notes shall have been authenticated and delivered pursuant to the terms of
Section 2.6; and

                (d) Notes converted into Common Stock pursuant to Article XV and
Notes deemed not outstanding pursuant to Article III.

                                      -5-
<PAGE>
 
          PAYMENT BLOCKAGE NOTICE: The term "Payment Blockage Notice" shall have
the meaning specified in Section 4.2.

          PERSON:  The term "Person" shall mean a corporation, an association, a
partnership, a limited liability corporation, an individual, a joint venture, a
joint stock company, a trust, an unincorporated organization or a government or
an agency or a political subdivision thereof.

          PORTAL MARKET:  The term "The Portal Market" shall mean The Portal
Market operated by the National Association of Securities Dealers, Inc. or any
successor thereto.

          PREDECESSOR NOTE:  The term "Predecessor Note" of any particular Note
shall mean every previous Note evidencing all or a portion of the same debt as
that evidenced by such particular Note; and, for the purposes of this
definition, any Note authenticated and delivered under Section 2.6 in lieu of a
lost, destroyed or stolen Note shall be deemed to evidence the same debt as the
lost, destroyed or stolen Note that it replaces.

          QIB: The term "QIB" shall mean a "qualified institutional buyer" as
defined in Rule 144A.

          REGISTRATION RIGHTS AGREEMENT:  The term "Registration Rights
Agreement" shall mean that certain Registration Rights Agreement, dated as of
March 15, 1998, between the Company and the Initial Purchasers, as amended from
time to time in accordance with its terms.

          REPRESENTATIVE: The term "Representative" shall mean the (a) indenture
trustee or other trustee, agent or representative for any Senior Indebtedness or
(b) with respect to any Senior Indebtedness that does not have any such trustee,
agent or other representative, (i) in the case of such Senior Indebtedness
issued pursuant to an agreement providing for voting arrangements as among the
holders or owners of such Senior Indebtedness, any holder or owner of such
Senior Indebtedness acting with the consent of the required Persons necessary to
bind such holders or owners of such Senior Indebtedness and (ii) in the case of
all other such Senior Indebtedness, the holder or owner of such Senior
Indebtedness.

          RESPONSIBLE OFFICER: The term "Responsible Officer," when used with
respect to the Trustee, shall mean an officer of the Trustee in the Corporate
Trust Office assigned and duly authorized by the Trustee to administer this
Indenture.

          RESTRICTED SECURITIES: The term "Restricted Securities" shall have the
meaning specified in Section 2.5(d).

          RULE 144A: The term "Rule 144A" shall mean Rule 144A as promulgated
under the Securities Act.

                                      -6-
<PAGE>
 
          SECURITIES ACT:  The term "Securities Act" shall mean the Securities
Act of 1933, as amended, and the rules and regulations promulgated thereunder.

          SENIOR INDEBTEDNESS:  The term "Senior Indebtedness" shall mean the
principal of, premium, if any, interest (including all interest accruing
subsequent to the commencement of any bankruptcy or similar proceeding, whether
or not a claim for post-petition interest is allowable as a claim in any such
proceeding) and rent payable on or in connection with, and all fees, costs,
expenses and other amounts accrued or due on or in connection with, Indebtedness
of the Company, whether outstanding on the date of this Indenture or thereafter
created, incurred, assumed, guaranteed or in effect guaranteed by the Company
(including all deferrals, renewals, extensions or refundings of, or amendments,
modifications or supplements to, the foregoing), unless in the case of any
particular Indebtedness the instrument creating or evidencing the same or the
assumption or guarantee thereof expressly provides that such Indebtedness shall
not be senior in right of payment to the Notes or expressly provides that such
Indebtedness is "pari passu" or " junior" to the Notes.  Notwithstanding the
foregoing, the term Senior Indebtedness shall not include any Indebtedness of
the Company to any subsidiary of the Company, a majority of the voting stock of
which is owned, directly or indirectly, by the Company.  If any payment made to
any holder of any Senior Indebtedness or its Representative with respect to such
Senior Indebtedness is rescinded or must otherwise be returned by such holder or
Representative upon the insolvency, bankruptcy or reorganization of the Company
or otherwise, the reinstated Indebtedness of the Company arising as a result of
such rescission or return shall constitute Senior Indebtedness effective as of
the date of such rescission or return.

          SIGNIFICANT SUBSIDIARY:  The term "Significant Subsidiary" shall mean,
as of any date of determination, a Subsidiary of the Company that would
constitute a "significant subsidiary" as such term is defined under Rule 1-02 of
Regulation S-X of the Commission.

          SUBSIDIARY:  The term "Subsidiary" shall mean, with respect to any
Person, (i) any corporation, association or other business entity of which more
than 50% of the total voting power of shares of capital stock entitled (without
regard to the occurrence of any contingency) to vote in the election of
directors, managers or trustees thereof is at the time owned or controlled,
directly or indirectly, by such Person or one or more of the other subsidiaries
of that Person (or a combination thereof) and (ii) any partnership (a) the sole
general partner or managing general partner of which is such Person or a
subsidiary of such Person or (b) the only general partners of which are such
Person or of one or more subsidiaries of such Person (or any combination
thereof).

          TRADING DAY: The term "Trading Day" shall have the meaning specified
in Section 15.5(h)(5).

          TRIGGER EVENT: The term "Trigger Event" shall have the meaning
specified in Section 15.5(d).

          TRUST INDENTURE ACT:  The term "Trust Indenture Act" shall mean the
Trust Indenture Act of 1939, as amended, as it was in force at the date of
execution of this Indenture, except as provided in Sections 11.3 and 15.6;
provided, however, that in the event the Trust Indenture Act of 1939 is

                                      -7-
<PAGE>
 
amended after the date hereof, the term "Trust Indenture Act" shall mean, to the
extent required by such amendment, the Trust Indenture Act of 1939 as so
amended.

          TRUSTEE:  The term "Trustee" shall mean Marine Midland Bank and its
successors and any corporation resulting from or surviving any consolidation or
merger to which it or its successors may be a party and any successor trustee at
the time serving as successor trustee hereunder.

     The definitions of certain other terms are as specified in Sections 2.5,
3.5 and Article XV.


                                    ARTICLE

       ISSUE, DESCRIPTION, EXECUTION, REGISTRATION AND EXCHANGE OF NOTES

     SECTION 2.1  DESIGNATION AMOUNT AND ISSUE OF NOTES.  The Notes shall be
designated as "5 3/4% Convertible Subordinated Notes due 2005."  Notes not to
exceed the aggregate principal amount of $100,000,000 (or $115,000,000 if the
over-allotment option set forth in Section 2 of the Purchase Agreement dated
March 24, 1998 (as amended from time to time by the parties thereto) by and
between the Company and the Initial Purchasers is exercised in full) (except
pursuant to Sections 2.5, 2.6, 3.3, 3.5 and 15.2 hereof) upon the execution of
this Indenture, or from time to time thereafter, may be executed by the Company
and delivered to the Trustee for authentication, and the Trustee shall thereupon
authenticate and deliver said Notes to or upon the written order of the Company,
signed by its (a) Chief Executive Officer, President, Executive or Senior Vice
President or any Vice President (whether or not designated by a number or
numbers or word or words added before or after the title "Vice President") and
(b) Treasurer or Assistant Treasurer or its Secretary or any Assistant
Secretary, without any further action by the Company hereunder.

     SECTION 2.2  FORM OF NOTES.  The Notes and the Trustee's certificate of
authentication to be borne by such Notes shall be substantially in the form set
forth in Exhibit A, which is incorporated in and made a part of this Indenture.
         ---------                                                             

     Any of the Notes may have such letters, numbers or other marks of
identification and such notations, legends and endorsements as the officers
executing the same may approve (execution thereof to be conclusive evidence of
such approval) and as are not inconsistent with the provisions of this
Indenture, or as may be required to comply with any law or with any rule or
regulation made pursuant thereto or with any rule or regulation of any
securities exchange or automated quotation system on which the Notes may be
listed, or to conform to usage.

     Any Note in global form shall represent such of the outstanding Notes as
shall be specified therein and shall provide that it shall represent the
aggregate amount of outstanding Notes from time to time endorsed thereon and
that the aggregate amount of outstanding Notes represented thereby may from time
to time be increased or reduced to reflect transfers or exchanges permitted
hereby.  Any endorsement of a Note in global form to reflect the amount of any
increase or decrease in the amount of outstanding Notes represented thereby
shall be made by the Trustee or the Custodian, at the direction

                                      -8-
<PAGE>
 
of the Trustee, in such manner and upon instructions given by the holder of such
Notes in accordance with this Indenture.  Payment of principal of and interest
and premium, if any, on any Note in global form shall be made to the holder of
such Note.

     The terms and provisions contained in the form of Note attached as Exhibit
                                                                        -------
A hereto shall constitute, and are hereby expressly made, a part of this
- -                                                                       
Indenture and, to the extent applicable, the Company and the Trustee, by their
execution and delivery of this Indenture, expressly agree to such terms and
provisions and to be bound thereby.

     SECTION 2.3  DATE AND DENOMINATION OF NOTES; PAYMENTS OF INTEREST. The
Notes shall be issuable in registered form without coupons in denominations of
$1,000 principal amount and integral multiples thereof. Every Note shall be
dated the date of its authentication and shall bear interest from the applicable
date in each case as specified on the face of the form of Note attached as
Exhibit A hereto. Interest on the Notes shall be computed on the basis of a 360-
- ---------
day year comprised of twelve (12) 30-day months.

     The Person in whose name any Note (or its Predecessor Note) is registered
on the Note register at the close of business on any record date with respect to
any interest payment date shall be entitled to receive the interest payable on
such interest payment date, except (i) that the interest payable upon redemption
(unless the date of redemption is an interest payment date) will be payable to
the Person to whom principal is payable and (ii) as set forth in the next
succeeding sentence.  In the case of any Note (or portion thereof) which is
converted into Common Stock of the Company during the period from (but
excluding) a record date to (but excluding) the next succeeding interest payment
date either (i) if such Note (or portion thereof) has been called for redemption
on a redemption date which occurs during such period, or is to be redeemed in
connection with a Fundamental Change on a Repurchase Date (as defined in Section
3.5) which occurs during such period, the Company shall not be required to pay
interest on such interest payment date in respect of any such Note (or portion
thereof) except to the extent required to be paid upon redemption of such Note
or portion thereof pursuant to Section 3.3 or 3.5 hereof or (ii) if otherwise,
any Note (or portion thereof) submitted for conversion during such period shall
be accompanied by funds equal to the interest payable on such succeeding
interest payment date on the principal amount so converted.  Interest shall be
payable at the office of the Company maintained by the Company for such purposes
in The Borough of Manhattan, the City of New York, which shall initially be an
office or agency of the Trustee and may, as the Company shall specify to the
paying agent in writing by each record date, be paid either (i) by check mailed
to the address of the Person entitled thereto as it appears in the Note register
(provided that the holder of Notes with an aggregate principal amount in excess
of $2,000,000 shall, at the written election of such holder, be paid by wire
transfer in immediately available funds) or (ii) by transfer to an account
maintained by such Person located in the United States; provided, however, that
payments to the Depositary will be made by wire transfer of immediately
available funds to the account of the Depositary or its nominee.  The term
"record date" with respect to any interest payment date shall mean March 15 or
September 15 preceding said April 1 or October 1, respectively.

     Any interest on any Note which is payable, but is not punctually paid or
duly provided for, on any said April 1 or October 1 (herein called "Defaulted
Interest") shall forthwith cease to be payable to

                                      -9-
<PAGE>
 
the Noteholder on the relevant record date by virtue of his having been such
Noteholder; and such Defaulted Interest shall 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 Notes (or their respective Predecessor Notes) 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 notify the Trustee in writing of the amount of Defaulted Interest
to be paid on each Note and the date of the payment (which shall be not less
than twenty-five (25) days after the receipt by the Trustee of such notice,
unless the Trustee shall consent to an earlier date), and at the same time the
Company shall deposit with the Trustee an amount of money equal to the aggregate
amount 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
provided. Thereupon the Trustee shall fix a special record date for the payment
of such Defaulted Interest which shall be not more than fifteen (15) days and
not less than ten (10) days prior to the date of the proposed payment, and not
less than ten (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 Noteholder at
his address as it appears in the Note register, not less than ten (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 Notes
(or their respective Predecessor Notes) were registered at the close of business
on such special record date and shall no longer be payable pursuant to the
following clause (2) of this Section 2.3.

          (2) The Company may make payment of any Defaulted Interest in any
other lawful manner not inconsistent with the requirements of any securities
exchange or automated quotation system on which the Notes may be listed or
designated for issuance, and upon such notice as may be required by such
exchange or automated quotation system, if, after notice given by the Company to
the Trustee of the proposed payment pursuant to this clause, such manner of
payment shall be deemed practicable by the Trustee.

     SECTION 2.4  EXECUTION OF NOTES. The Notes shall be signed in the name and
on behalf of the Company by the manual or facsimile signature of its Chief
Executive Officer, President, any Executive or Senior Vice President or any Vice
President (whether or not designated by a number or numbers or word or words
added before or after the title "Vice President") and attested by the manual or
facsimile signature of its Secretary or any of its Assistant Secretaries or
Treasurer or any of its Assistant Treasurers (which may be printed, engraved or
otherwise reproduced thereon, by facsimile or otherwise). Only such Notes as
shall bear thereon a certificate of authentication substantially in the form set
forth on the form of Note attached as Exhibit A hereto, manually executed by the
                                      ---------                                 
Trustee (or an authenticating agent appointed by the Trustee as provided by
Section 16.11), shall be entitled to the benefits of this Indenture or be valid
or obligatory for any purpose.  Such certificate by the Trustee (or such an
authenticating agent) upon any Note executed by the Company shall be conclusive
evidence that the Note so

                                     -10-
<PAGE>
 
authenticated has been duly authenticated and delivered hereunder and that the
holder is entitled to the benefits of this Indenture.

     In case any officer of the Company who shall have signed any of the Notes
shall cease to be such officer before the Notes so signed shall have been
authenticated and delivered by the Trustee, or disposed of by the Company, such
Notes nevertheless may be authenticated and delivered or disposed of as though
the person who signed such Notes had not ceased to be such officer of the
Company; and any Note may be signed on behalf of the Company by such persons as,
at the actual date of the execution of such Note, shall be the proper officers
of the Company, although at the date of the execution of this Indenture any such
person was not such an officer.

     SECTION 2.5  EXCHANGE AND REGISTRATION OF TRANSFER OF NOTES: RESTRICTIONS
                  ON TRANSFER; DEPOSITARY.

                  (a) The Company shall cause to be kept at the Corporate Trust
Office a register (the register maintained in such office and in any other
office or agency of the Company designated pursuant to Section 5.2 being herein
sometimes collectively referred to as the "Note register") in which, subject to
such reasonable regulations as it may prescribe, the Company shall provide for
the registration of Notes and of transfers of Notes. The Note register shall be
in written form or in any form capable of being converted into written form
within a reasonably prompt period of time. The Trustee is hereby appointed "Note
registrar" for the purpose of registering Notes and transfers of Notes as herein
provided. The Company may appoint one or more co-registrars in accordance with
Section 5.2.

     Upon surrender for registration of transfer of any Note to the Note
registrar or any co-registrar, and satisfaction of the requirements for such
transfer set forth in this Section 2.5, the Company shall execute, and the
Trustee shall authenticate and deliver, in the name of the designated transferee
or transferees, one or more new Notes of any authorized denominations and of a
like aggregate principal amount and bearing such restrictive legends as may be
required by this Indenture.

     Notes may be exchanged for other Notes of any authorized denominations and
of a like aggregate principal amount, upon surrender of the Notes to be
exchanged at any such office or agency maintained by the Company pursuant to
Section 5.2.  Whenever any Notes are so surrendered for exchange, the Company
shall execute, and the Trustee shall authenticate and deliver, the Notes which
the Noteholder making the exchange is entitled to receive bearing registration
numbers not contemporaneously outstanding.

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

     All Notes presented or surrendered for registration of transfer or for
exchange, redemption or conversion shall (if so required by the Company or the
Note registrar) be duly endorsed, or be accompanied by a written instrument or
instruments of transfer in form satisfactory to the Company, and the Notes shall
be duly executed by the Noteholder thereof or his attorney duly authorized in
writing.

                                     -11-
<PAGE>
 
     No service charge shall be made for any registration of transfer or
exchange of Notes, but the Company may require payment of a sum sufficient to
cover any tax, assessment or other governmental charge that may be imposed in
connection with any registration of transfer or exchange of Notes.

     Neither the Company nor the Trustee nor any Note registrar shall be
required to exchange or register a transfer of (a) any Notes for a period of
fifteen (15) days next preceding any selection of Notes to be redeemed or (b)
any Notes or portions thereof called for redemption pursuant to Section 3.2 or
(c) any Notes or portion thereof surrendered for conversion pursuant to Article
XV or (d) any Notes or portions thereof tendered for redemption (and not
withdrawn) pursuant to Section 3.5.

          (b) So long as the Notes are eligible for book-entry settlement with
the Depositary, or unless otherwise required by law, all Notes that upon initial
issuance are beneficially owned by QIBs and as a result of a sale or transfer
after initial issuance will be represented by one or more Notes in global form
registered in the name of the Depositary or the nominee of the Depositary (the
"Global Note"), except as otherwise specified below. The transfer and exchange
of beneficial interests in any such Global Note shall be effected through the
Depositary in accordance with this Indenture and the procedures of the
Depositary therefor. The Trustee shall make appropriate endorsements to reflect
increases or decreases in the principal amounts of any such Global Note as set
forth on the face of the Note ("Principal Amount") to reflect any such
transfers. Except as provided below, beneficial owners of a Global Note shall
not be entitled to have certificates registered in their names, will not receive
or be entitled to receive physical delivery of certificates in definitive form
and will not be considered holders of such Notes in global form.

          (c) So long as the Notes are eligible for book-entry settlement, or
unless otherwise required by law, upon any transfer of a definitive Note to a
QIB in accordance with Rule 144A, and upon receipt of the definitive Note or
Notes being so transferred, together with a certification, substantially in the
form on the reverse of the Note, from the transferor that the transfer is being
made in compliance with Rule 144A (or other evidence satisfactory to the
Trustee), the Trustee shall make an endorsement on the Global Note to reflect an
increase in the aggregate Principal Amount of the Notes represented by such Note
in global form, and the Trustee shall cancel such definitive Note or Notes in
accordance with the standing instructions and procedures of the Depositary, the
aggregate Principal Amount of Notes represented by such Note in global form to
be increased accordingly; provided that no definitive Note, or portion thereof,
in respect of which the Company or an Affiliate of the Company held any
beneficial interest shall be included in such Note in global form until such
definitive Note is freely tradable in accordance with Rule 144(k); provided
further that the Trustee shall issue Notes in definitive form upon any transfer
of a beneficial interest in the Note in global form to the Company or any
Affiliate of the Company.

     Upon any sale or transfer of a Note to an Institutional Accredited Investor
(other than pursuant to a registration statement that has been declared
effective under the Securities Act), such Institutional Accredited Investor
shall, prior to such sale or transfer, furnish to the Company and/or the Trustee
a signed letter containing representations and agreements relating to
restrictions on transfer substantially in the form set forth in Exhibit B to
                                                                ---------   
this Indenture.

                                     -12-
<PAGE>
 
     Any Note in global form may be endorsed with or have incorporated in the
text thereof such legends or recitals or changes not inconsistent with the
provisions of this Indenture as may be required by the Custodian, the Depositary
or by the National Association of Securities Dealers, Inc. in order for the
Notes to be tradeable on The Portal Market or as may be required for the Notes
to be tradeable on any other market developed for trading of securities pursuant
to Rule 144A or required to comply with any applicable law or any regulation
thereunder or with the rules and regulations of any securities exchange or
automated quotation system upon which the Notes may be listed or traded or to
conform with any usage with respect thereto, or to indicate any special
limitations or restrictions to which any particular Notes are subject.

          (d) Every Note that bears or is required under this Section 2.5(d) to
bear the legend set forth in this Section 2.5(d) (together with any Common Stock
issued upon conversion of the Notes and required to bear the legend set forth in
Section 2.5(e), collectively, the "Restricted Securities") shall be subject to
the restrictions on transfer set forth in this Section 2.5(d) (including those
set forth in the legend set forth below) unless such restrictions on transfer
shall be waived by written consent of the Company, and the holder of each such
Restricted Note, by such Noteholder's acceptance thereof, agrees to be bound by
all such restrictions on transfer. As used in Sections 2.5(d) and 2.5(e), the
term "transfer" encompasses any sale, pledge, transfer or other disposition
whatsoever of any Restricted Security.

     Until the expiration of the holding period applicable to sales thereof
under Rule 144(k) under the Securities Act (or any successor provision), any
certificate evidencing such Note (and all securities issued in exchange therefor
or substitution thereof, other than Common Stock, if any, issued upon conversion
thereof, which shall bear the legend set forth in Section 2.5(e), if applicable)
shall bear a legend in substantially the following form, unless such Note has
been sold pursuant to a registration statement that has been declared effective
under the Securities Act (and which continues to be effective at the time of
such transfer), or unless otherwise agreed by the Company in writing, with
written notice thereof to the Trustee:

THE NOTE EVIDENCED HEREBY HAS NOT BEEN REGISTERED UNDER THE UNITED STATES
SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR ANY STATE
SECURITIES LAWS, AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD EXCEPT AS SET
FORTH IN THE FOLLOWING SENTENCE.  BY ITS ACQUISITION HEREOF, THE HOLDER (1)
REPRESENTS THAT (A) IT IS A "QUALIFIED INSTITUTIONAL BUYER" (AS DEFINED IN RULE
144A UNDER THE SECURITIES ACT) OR (B) IT IS AN INSTITUTIONAL "ACCREDITED
INVESTOR" (AS DEFINED IN RULE 501(A)(1), (2), (3) OR (7) UNDER THE SECURITIES
ACT) ("INSTITUTIONAL ACCREDITED INVESTOR"); (2) AGREES THAT IT WILL NOT, PRIOR
TO EXPIRATION OF THE HOLDING PERIOD APPLICABLE TO SALES OF THE NOTE EVIDENCED
HEREBY UNDER RULE 144(K) UNDER THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION),
RESELL OR OTHERWISE TRANSFER THE NOTE EVIDENCED HEREBY OR THE COMMON STOCK
ISSUABLE UPON CONVERSION OF SUCH NOTE EXCEPT (A) TO AVIRON OR ANY SUBSIDIARY
THEREOF, (B) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A

                                     -13-
<PAGE>
 
UNDER THE SECURITIES ACT, (C) TO AN INSTITUTIONAL ACCREDITED INVESTOR THAT,
PRIOR TO SUCH TRANSFER, FURNISHES TO MARINE MIDLAND BANK, AS TRUSTEE (OR A
SUCCESSOR TRUSTEE, AS APPLICABLE), A SIGNED LETTER CONTAINING CERTAIN REPRE-
SENTATIONS AND AGREEMENTS RELATING TO THE RESTRICTIONS ON TRANSFER OF THE NOTE
EVIDENCED HEREBY (THE FORM OF WHICH LETTER CAN BE OBTAINED FROM SUCH TRUSTEE OR
A SUCCESSOR TRUSTEE, AS APPLICABLE), (D) PURSUANT TO THE EXEMPTION FROM
REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT (IF AVAILABLE) OR (E)
PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BEEN DECLARED EFFECTIVE UNDER THE
SECURITIES ACT (AND WHICH CONTINUES TO BE EFFECTIVE AT THE TIME OF SUCH
TRANSFER); (3) PRIOR TO SUCH TRANSFER (OTHER THAN A TRANSFER PURSUANT TO CLAUSE
2(E) ABOVE), IT WILL FURNISH TO MARINE MIDLAND BANK, AS TRUSTEE (OR A SUCCESSOR
TRUSTEE, AS APPLICABLE), SUCH CERTIFICATIONS, LEGAL OPINIONS OR OTHER
INFORMATION AS IT MAY REASONABLY REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING
MADE PURSUANT TO AN EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE
REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND (4) AGREES THAT IT WILL
DELIVER TO EACH PERSON TO WHOM THE NOTE EVIDENCED HEREBY IS TRANSFERRED A NOTICE
SUBSTANTIALLY TO THE EFFECT OF THIS LEGEND.  IN CONNECTION WITH ANY TRANSFER OF
THE NOTE EVIDENCED HEREBY PRIOR TO THE EXPIRATION OF THE HOLDING PERIOD
APPLICABLE TO SALES OF THE NOTE EVIDENCED HEREBY UNDER RULE 144(K) UNDER THE
SECURITIES ACT (OR ANY SUCCESSOR PROVISION), THE HOLDER MUST CHECK THE
APPROPRIATE BOX SET FORTH ON THE REVERSE HEREOF RELATING TO THE MANNER OF SUCH
TRANSFER AND SUBMIT THIS CERTIFICATE TO MARINE MIDLAND BANK, AS TRUSTEE (OR A
SUCCESSOR TRUSTEE, AS APPLICABLE).  IF THE PROPOSED TRANSFEREE IS AN
INSTITUTIONAL ACCREDITED INVESTOR, THE HOLDER MUST, PRIOR TO SUCH TRANSFER,
FURNISH TO MARINE MIDLAND BANK, AS TRUSTEE (OR A SUCCESSOR TRUSTEE, AS
APPLICABLE), SUCH CERTIFICATIONS, LEGAL OPINIONS OR OTHER INFORMATION AS IT MAY
REASONABLY REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING MADE PURSUANT TO AN
EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION
REQUIREMENTS OF THE SECURITIES ACT.  THIS LEGEND WILL BE REMOVED UPON THE
EARLIER OF THE TRANSFER OF THE NOTE EVIDENCED HEREBY PURSUANT TO CLAUSE 2(E)
ABOVE OR UPON ANY TRANSFER OF THE NOTE EVIDENCED HEREBY UNDER RULE 144(K) UNDER
THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION).

     Any Note (or security issued in exchange or substitution therefor) as to
which such restrictions on transfer shall have expired in accordance with their
terms or as to the conditions for removal of the

                                     -14-
<PAGE>
 
foregoing legend set forth therein have been satisfied may, upon surrender of
such Note for exchange to the Note registrar in accordance with the provisions
of this Section 2.5, be exchanged for a new Note or Notes, of like tenor and
aggregate principal amount, which shall not bear the restrictive legend required
by this Section 2.5(d).

     Notwithstanding any other provisions of this Indenture (other than the
provisions set forth in the second paragraph of Section 2.5(b) and in this
Section 2.5(d)), a Note in global form may not be transferred as a whole or in
part except by the Depositary to a nominee of the Depositary or by a nominee of
the Depositary to the Depositary or another nominee of the Depositary or by the
Depositary or any such nominee to a successor Depositary or a nominee of such
successor Depositary.

     The Depositary shall be a clearing agency registered under the Exchange
Act.  The Company initially appoints The Depository Trust Company to act as
Depositary with respect to the Notes in global form.  Initially, the Global Note
shall be issued to the Depositary, registered in the name of Cede & Co., as the
nominee of the Depositary, and deposited with the Custodian for Cede & Co.

     If at any time the Depositary for a Note in global form notifies the
Company that it is unwilling or unable to continue as Depositary for such Note,
the Company may appoint a successor Depositary with respect to such Note.  If a
successor Depositary is not appointed by the Company within ninety (90) days
after the Company receives such notice, the Company will execute, and the
Trustee, upon receipt of an Officers' Certificate for the authentication and
delivery of Notes, will authenticate and deliver, Notes in certificated form, in
aggregate principal amount equal to the principal amount of such Note in global
form, in exchange for such Note in global form.

     If a Note in certificated form is issued in exchange for any portion of a
Note in global form after the close of business at the office or agency where
such exchange occurs on any record date and before the opening of business at
such office or agency on the next succeeding interest payment date, interest
will not be payable on such interest payment date in respect of such Note, but
will be payable on such interest payment date, subject to the provisions of
Section 2.3, only to the Person to whom interest in respect of such portion of
such Note in global form is payable in accordance with the provisions of this
Indenture.

     Notes in certificated form issued in exchange for all or a part of a Note
in global form pursuant to this Section 2.5 shall be registered in such names
and in such authorized denominations as the Depositary, pursuant to instructions
from its direct or indirect participants or otherwise, shall instruct the
Trustee.  Upon execution and authentication, the Trustee shall deliver such
Notes in certificated form to the Persons in whose names such Notes in
certificated form are so registered.

     At such time as all interests in a Note in global form have been redeemed,
converted, canceled, exchanged for Notes in certificated form, or transferred to
a transferee who receives Notes in certificated form thereof, such Note in
global form shall, upon receipt thereof, be canceled by the Trustee in
accordance with standing procedures and instructions existing between the
Depositary and the Custodian.  At any time prior to such cancellation, if any
interest in a global Note is exchanged for Notes in certificated form, redeemed,
converted, repurchased or canceled, exchanged for Notes in certificated

                                     -15-
<PAGE>
 
form or transferred to a transferee who receives Notes in certificated form
therefor or any Note in certificated form is exchanged or transferred for part
of a Note in global form, the principal amount of such Note in global form
shall, in accordance with the standing procedures and instructions existing
between the Depositary and the Custodian, be appropriately reduced or increased,
as the case may be, and an endorsement shall be made on such Note in global
form, by the Trustee or the Custodian, at the direction of the Trustee, to
reflect such reduction or increase.

          (e) Until the expiration of the holding period applicable to sales
thereof under Rule 144(k) under the Securities Act (or any successor provision),
any stock certificate representing Common Stock issued upon conversion of any
Note shall bear a legend in substantially the following form, unless such Common
Stock has been sold pursuant to a registration statement that has been declared
effective under the Securities Act (and which continues to be effective at the
time of such transfer) or such Common Stock has been issued upon conversion of
Notes that have been transferred pursuant to a registration statement that has
been declared effective under the Securities Act, or unless otherwise agreed by
the Company in writing with written notice thereof to the transfer agent:

THE COMMON STOCK EVIDENCED HEREBY HAS NOT BEEN REGISTERED UNDER THE UNITED
STATES SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR ANY STATE
SECURITIES LAWS, AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD EXCEPT AS SET
FORTH IN THE FOLLOWING SENTENCE.  THE HOLDER HEREOF AGREES THAT UNTIL THE
EXPIRATION OF THE HOLDING PERIOD APPLICABLE TO SALES OF THE SECURITY EVIDENCED
HEREBY UNDER RULE 144(K) UNDER THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION),
(1) IT WILL NOT RESELL OR OTHERWISE TRANSFER THE COMMON STOCK EVIDENCED HEREBY
EXCEPT (A) TO AVIRON OR ANY SUBSIDIARY THEREOF, (B) TO A "QUALIFIED
INSTITUTIONAL BUYER" (AS DEFINED IN RULE 144A UNDER THE SECURITIES ACT) IN
COMPLIANCE WITH RULE 144A, (C) TO AN INSTITUTIONAL "ACCREDITED INVESTOR" (AS
DEFINED IN RULE 501(A)(1), (2), (3) OR (7) UNDER THE SECURITIES ACT) THAT PRIOR
TO SUCH TRANSFER FURNISHES TO BOSTON EQUISERVE L.L.P., AS TRANSFER AGENT (OR A
SUCCESSOR TRANSFER AGENT, AS APPLICABLE), A SIGNED LETTER CONTAINING CERTAIN
REPRESENTATIONS AND AGREEMENTS RELATING TO THE RESTRICTIONS ON TRANSFER OF THE
COMMON STOCK EVIDENCED HEREBY (THE FORM OF WHICH LETTER CAN BE OBTAINED FROM
SUCH TRANSFER AGENT OR A SUCCESSOR TRANSFER AGENT, AS APPLICABLE), (D) PURSUANT
TO THE EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT
(IF AVAILABLE), OR (E) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BEEN
DECLARED EFFECTIVE UNDER THE SECURITIES ACT (AND WHICH CONTINUES TO BE EFFECTIVE
AT THE TIME OF SUCH TRANSFER); (2) PRIOR TO SUCH TRANSFER (OTHER THAN A TRANSFER
PURSUANT TO CLAUSE 1(E) ABOVE), IT WILL FURNISH TO BOSTON EQUISERVE L.L.P., AS
TRANSFER AGENT (OR A SUCCESSOR TRANSFER AGENT, AS APPLICABLE),

                                     -16-
<PAGE>
 
SUCH CERTIFICATIONS, LEGAL OPINIONS OR OTHER INFORMATION AS IT MAY REASONABLY
REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING MADE PURSUANT TO AN EXEMPTION
FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE
SECURITIES ACT AND (3) IT WILL DELIVER TO EACH PERSON TO WHOM THE COMMON STOCK
EVIDENCED HEREBY IS TRANSFERRED (OTHER THAN A TRANSFER PURSUANT TO CLAUSE 1(E)
ABOVE) A NOTICE SUBSTANTIALLY TO THE EFFECT OF THIS LEGEND.  THIS LEGEND WILL BE
REMOVED UPON THE EARLIER OF THE TRANSFER OF THE COMMON STOCK EVIDENCED HEREBY
PURSUANT TO CLAUSE 1(E) ABOVE OR UPON ANY TRANSFER OF THE COMMON STOCK EVIDENCED
HEREBY AFTER THE EXPIRATION OF THE HOLDING PERIOD APPLICABLE TO SALES OF THE
SECURITY EVIDENCED HEREBY UNDER RULE 144(K) UNDER THE SECURITIES ACT (OR ANY
SUCCESSOR PROVISION).

     Any such Common Stock as to which such restrictions on transfer shall have
expired in accordance with their terms or as to which the conditions for removal
of the foregoing legend set forth therein have been satisfied may, upon
surrender of the certificates representing such shares of Common Stock for
exchange in accordance with the procedures of the transfer agent for the Common
Stock, be exchanged for a new certificate or certificates for a like number of
shares of Common Stock, which shall not bear the restrictive legend required by
this Section 2.5(e).

          (f) Any Note or Common Stock issued upon the conversion or exchange of
a Note that, prior to the expiration of the holding period applicable to sales
thereof under Rule 144(k) under the Securities Act (or any successor provision),
is purchased or owned by the Company or any Affiliate thereof may not be resold
by the Company or such Affiliate unless registered under the Securities Act or
resold pursuant to an exemption from the registration requirements of the
Securities Act in a transaction which results in such Notes or Common Stock, as
the case may be, no longer being "restricted securities" (as defined under Rule
144).

     SECTION 2.6  MUTILATED, DESTROYED, LOST OR STOLEN NOTES.  In case any Note
shall become mutilated or be destroyed, lost or stolen, the Company in its
discretion may execute, and upon its written request the Trustee or an
authenticating agent appointed by the Trustee shall authenticate and make
available for delivery, a new Note, bearing a number not contemporaneously
outstanding, in exchange and substitution for the mutilated Note, or in lieu of
and in substitution for the Note so destroyed, lost or stolen.  In every case
the applicant for a substituted Note shall furnish to the Company, to the
Trustee and, if applicable, to such authenticating agent such security or
indemnity as may be required by them to save each of them harmless for any loss,
liability, cost or expense caused by or connected with such substitution, and,
in every case of destruction, loss or theft, the applicant shall also furnish to
the Company, to the Trustee and, if applicable, to such authenticating agent
evidence to their satisfaction of the destruction, loss or theft of such Note
and of the ownership thereof.

     Following receipt by the Trustee or such authenticating agent, as the case
may be, of satisfactory security or indemnity and evidence, as described in the
preceding paragraph, the Trustee or such

                                     -17-
<PAGE>
 
authenticating agent may authenticate any such substituted Note and make
available for delivery such Note.  Upon the issuance of any substituted Note,
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 connected therewith.  In case any Note which has matured or is about to
mature or has been called for redemption or has been tendered for redemption
(and not withdrawn) or is about to be converted into Common Stock shall become
mutilated or be destroyed, lost or stolen, the Company may, instead of issuing a
substitute Note, pay or authorize the payment of or convert or authorize the
conversion of the same (without surrender thereof except in the case of a
mutilated Note), as the case may be, if the applicant for such payment or
conversion shall furnish to the Company, to the Trustee and, if applicable, to
such authenticating agent such security or indemnity as may be required by them
to save each of them harmless for any loss, liability, cost or expense caused by
or connected with such substitution, and, in case of destruction, loss or theft,
evidence satisfactory to the Company, the Trustee and, if applicable, any paying
agent or conversion agent of the destruction, loss or theft of such Note and of
the ownership thereof.

     Every substitute Note issued pursuant to the provisions of this Section 2.6
by virtue of the fact that any Note is destroyed, lost or stolen shall
constitute an additional contractual obligation of the Company, whether or not
the destroyed, lost or stolen Note shall be found at any time, and shall be
entitled to all the benefits of (but shall be subject to all the limitations set
forth in) this Indenture equally and proportionately with any and all other
Notes duly issued hereunder.  To the extent permitted by law, all Notes shall be
held and owned upon the express condition that the foregoing provisions are
exclusive with respect to the replacement or payment or conversion of mutilated,
destroyed, lost or stolen Notes and shall preclude any and all other rights or
remedies notwithstanding any law or statute existing or hereafter enacted to the
contrary with respect to the replacement or payment or conversion of negotiable
instruments or other securities without their surrender.

     SECTION 2.7  TEMPORARY NOTES.  Pending the preparation of Notes in
certificated form, the Company may execute and the Trustee or an authenticating
agent appointed by the Trustee shall, upon the written request of the Company,
authenticate and deliver temporary Notes (printed or lithographed).  Temporary
Notes shall be issuable in any authorized denomination, and substantially in the
form of the Notes in certificated form, but with such omissions, insertions and
variations as may be appropriate for temporary Notes, all as may be determined
by the Company.  Every such temporary Note shall be executed by the Company and
authenticated by the Trustee or such authenticating agent upon the same
conditions and in substantially the same manner, and with the same effect, as
the Notes in certificated form.  Without unreasonable delay the Company will
execute and deliver to the Trustee or such authenticating agent Notes in
certificated form (other than in the case of Notes in global form) and thereupon
any or all temporary Notes (other than any such Note in global form) may be
surrendered in exchange therefor, at each office or agency maintained by the
Company pursuant to Section 5.2 and the Trustee or such authenticating agent
shall authenticate and make available for delivery in exchange for such
temporary Notes an equal aggregate principal amount of Notes in certificated
form.  Such exchange shall be made by the Company at its own expense and without
any charge therefor.  Until so exchanged, the temporary Notes shall in all
respects be entitled to the same benefits and subject to the same limitations
under this Indenture as Notes in certificated form authenticated and delivered
hereunder.


                                     -18-
<PAGE>
 
     SECTION 2.8  CANCELLATION OF NOTES PAID, ETC. All Notes surrendered for the
purpose of payment, redemption, conversion, exchange or registration of
transfer, shall, if surrendered to the Company or any paying agent or any Note
registrar or any conversion agent, be surrendered to the Trustee and promptly
canceled by it, or, if surrendered to the Trustee, shall be promptly canceled by
it, and no Notes shall be issued in lieu thereof except as expressly permitted
by any of the provisions of this Indenture. The Trustee shall dispose of such
canceled Notes in accordance with its customary procedures. If the Company shall
acquire any of the Notes, such acquisition shall not operate as a redemption or
satisfaction of the indebtedness represented by such Notes unless and until the
same are delivered to the Trustee for cancellation.

     SECTION 2.9  CUSIP NUMBERS. The Company in issuing the Notes may use
"CUSIP" numbers (if then generally in use), and, if so, the Trustee shall use
"CUSIP" numbers in notices of redemption as a convenience to Noteholders;
provided that any such notice may state that no representation is made as to the
correctness of such numbers either as printed on the Notes or as contained in
any notice of a redemption and that reliance may be placed only on the other
identification numbers printed on the Notes, and any such redemption shall not
be affected by any defect in or omission of such numbers. The Company will
promptly notify the Trustee of any change in the CUSIP numbers.


                                  ARTICLE III

                              REDEMPTION OF NOTES

     SECTION 3.1  REDEMPTION PRICES. The Company may not redeem the Notes prior
to April 6, 2001. At any time on or after April 6, 2001, the Company may, at its
option, redeem all or from time to time any part of the Notes on any date prior
to maturity, upon notice as set forth in Section 3.2, and at the optional
redemption prices set forth in the form of Note attached as Exhibit A hereto,
                                                            ---------        
together with accrued interest to, but excluding, the date fixed for redemption.

     SECTION 3.2  NOTICE OF REDEMPTION; SELECTION OF NOTES.  In case the Company
shall desire to exercise the right to redeem all or, as the case may be, any
part of the Notes pursuant to Section 3.1, it shall fix a date for redemption
and it or, at its written request received by the Trustee not fewer than forty-
five (45) days prior (or such shorter period of time as may be acceptable to the
Trustee) to the date fixed for redemption, the Company, or at the request of the
Company, the Trustee in the name of and at the expense of the Company, shall
mail or cause to be mailed a notice of such redemption at least thirty (30) days
prior to the date fixed for redemption to the holders of Notes so to be redeemed
as a whole or in part at their last addresses as the same appear on the Note
register; provided that if the Company shall give such notice, it shall also
give written notice, and written notice of the Notes to be redeemed, to the
Trustee.  The Company may not give notice of any redemption of the Notes if a
default in payment of interest on the Notes has occurred and is continuing.
Such mailing shall be by first class mail.  The notice if mailed in the manner
herein provided shall be conclusively presumed to have been duly given, whether
or not the holder receives such notice.  In any case, failure to give such
notice by mail or any defect in the notice to the holder of any Note designated
for redemption as a whole or in part shall not affect the validity of the
proceedings for the redemption of any other Note.


                                     -19-
<PAGE>
 
     Each such notice of redemption shall specify the aggregate principal amount
of Notes to be redeemed, the CUSIP numbers or numbers of the Notes being
redeemed, the date fixed for redemption (which shall be a Business Day), the
redemption price at which Notes are to be redeemed, the place or places of
payment, that payment will be made upon presentation and surrender of such
Notes, that interest accrued to the date fixed for redemption will be paid as
specified in said notice, and that on and after said date interest thereon or on
the portion thereof to be redeemed will cease to accrue.  Such notice shall also
state the current Conversion Price and the date on which the right to convert
such Notes or portions thereof into Common Stock will expire.  If fewer than all
the Notes are to be redeemed, the notice of redemption shall identify the Notes
to be redeemed (including CUSIP numbers, if any).  In case any Note is to be
redeemed in part only, the notice of redemption shall state the portion of the
principal amount thereof to be redeemed and shall state that on and after the
date fixed for redemption, upon surrender of such Note, a new Note or Notes in
principal amount equal to the unredeemed portion thereof will be issued.

     On or prior to the redemption date specified in the notice of redemption
given as provided in this Section 3.2, the Company will deposit with the Trustee
or with one or more paying agents (or, if the Company is acting as its own
paying agent, set aside, segregate and hold in trust as provided in Section 5.4)
an amount of money sufficient to redeem on the redemption date all the Notes (or
portions thereof) so called for redemption (other than those theretofore
surrendered for conversion into Common Stock) at the appropriate redemption
price, together with accrued interest to, but excluding, the date fixed for
redemption; provided that if such payment is made on the redemption date it must
be received by the Trustee or paying agent, as the case may be, by 10:00 a.m.
New York City time, on such date.  If any Note called for redemption is
converted pursuant hereto, any money deposited with the Trustee or any paying
agent or so segregated and held in trust for the redemption of such Note shall
be paid to the Company upon its written request, or, if then held by the Company
shall be discharged from such trust.  Whenever any Notes are to be redeemed, the
Company will give the Trustee written notice in the form of an Officers'
Certificate not fewer than forty-five (45) days (or such shorter period of time
as may be acceptable to the Trustee) prior to the redemption date as to the
aggregate principal amount of Notes to be redeemed.

     If fewer than all the Notes are to be redeemed, the Trustee shall select
the Notes or portions thereof of the Global Note or the Notes in certificated
form to be redeemed (in principal amounts of $1,000 or integral multiples
thereof), by lot, on a pro rata basis or by another method the Trustee deems
fair and appropriate.  If any Note selected for partial redemption is converted
in part after such selection, the converted portion of such Note shall be deemed
(so far as may be) to be the portion to be selected for redemption.  The Notes
(or portions thereof) so selected shall be deemed duly selected for redemption
for all purposes hereof, notwithstanding that any such Note is converted as a
whole or in part before the mailing of the notice of redemption.

     Upon any redemption of less than all Notes, the Company and the Trustee may
(but need not) treat as outstanding any Notes surrendered for conversion during
the period of fifteen (15) days next preceding the mailing of a notice of
redemption and may (but need not) treat as outstanding any Note authenticated
and delivered during such period in exchange for the unconverted portion of any
Note converted in part during such period.



                                     -20-
<PAGE>
 
     SECTION 3.3  PAYMENT OF NOTES CALLED FOR REDEMPTION. If notice of
redemption has been given as above provided, the Notes or portion of Notes with
respect to which such notice has been given shall, unless converted into Common
Stock pursuant to the terms hereof, become due and payable on the date fixed for
redemption and at the place or places stated in such notice at the applicable
redemption price, together with interest accrued to (but excluding) the date
fixed for redemption, and on and after said date (unless the Company shall
default in the payment of such Notes at the redemption price, together with
interest accrued to said date), interest on the Notes or portion of Notes so
called for redemption shall cease to accrue and such Notes shall cease after the
close of business on the Business Day next preceding the date fixed for
redemption to be convertible into Common Stock and, except as provided in
Sections 8.5 and 13.4, to be entitled to any benefit or security under this
Indenture, and the holders thereof shall have no right in respect of such Notes
except the right to receive the redemption price thereof and unpaid interest to
(but excluding) the date fixed for redemption. On presentation and surrender of
such Notes at a place of payment in said notice specified, the said Notes or the
specified portions thereof shall be paid and redeemed by the Company at the
applicable redemption price, together with interest accrued thereon to (but
excluding) the date fixed for redemption; provided that, if the applicable
redemption date is an interest payment date, the semi-annual payment of interest
becoming due on such date shall be payable to the holders of such Notes
registered as such on the relevant record date instead of the holders
surrendering such Notes for redemption on such date.

     Upon presentation of any Note redeemed in part only, the Company shall
execute and the Trustee shall authenticate and make available for delivery to
the holder thereof, at the expense of the Company, a new Note or Notes, of
authorized denominations, in principal amount equal to the unredeemed portion of
the Notes so presented.

     Notwithstanding the foregoing, the Trustee shall not redeem any Notes or
mail any notice of optional redemption during the continuance of a default in
payment of interest on the Notes.  If any Note called for redemption shall not
be so paid upon surrender thereof for redemption, the principal and premium, if
any, shall, until paid or duly provided for, bear interest from the date fixed
for redemption at the rate borne by the Note and such Note shall remain
convertible into Common Stock until the principal and premium, if any, shall
have been paid or duly provided for.

     SECTION 3.4  CONVERSION ARRANGEMENT ON CALL FOR REDEMPTION.  In connection
with any redemption of Notes, the Company may arrange for the purchase and
conversion of any Notes by an agreement with one or more investment bankers or
other purchasers to purchase such Notes by paying to the Trustee in trust for
the Noteholders, on or before the date fixed for redemption, an amount not less
than the applicable redemption price, together with interest accrued to (but
excluding) the date fixed for redemption, of such Notes.  Notwithstanding
anything to the contrary contained in this Article III, the obligation of the
Company to pay the redemption price of such Notes, together with interest
accrued to (but excluding) the date fixed for redemption, shall be deemed to be
satisfied and discharged to the extent such amount is so paid by such
purchasers.  If such an agreement is entered into, a copy of which will be filed
with the Trustee prior to the date fixed for redemption, any Notes not duly
surrendered for conversion by the holders thereof may, at the option of the
Company, be deemed, to the fullest extent permitted by law, acquired by such
purchasers from such holders and (notwithstanding anything to the contrary
contained in Article XV) surrendered by such purchasers for conversion, all as
of immediately

                                     -21-
<PAGE>
 
prior to the close of business on the date fixed for redemption (and the right
to convert any such Notes shall be extended through such time), subject to
payment of the above amount as aforesaid.  At the direction of the Company, the
Trustee shall hold and dispose of any such amount paid to it in the same manner
as it would monies deposited with it by the Company for the redemption of Notes.
Without the Trustee's prior written consent, no arrangement between the Company
and such purchasers for the purchase and conversion of any Notes shall increase
or otherwise affect any of the powers, duties, responsibilities or obligations
of the Trustee as set forth in this Indenture.

     SECTION 3.5  REDEMPTION AT OPTION OF HOLDERS.

          (a) If there shall occur a Fundamental Change at any time prior to
maturity of the Notes, then each Noteholder shall have the right, at such
holder's option, to require the Company to redeem all of such holder's Notes, or
any portion thereof that is an integral multiple of $1,000 principal amount, on
the date (the "Repurchase Date") that is thirty (30) days after the date of the
Company Notice (as defined in Section 3.5(b) below) of such Fundamental Change
(or, if such 30th day is not a Business Day, the next succeeding Business Day)
at a redemption price equal to 100% of the principal amount thereof, together
with accrued interest to (but excluding) the Repurchase Date; provided that, if
such Repurchase Date is April 1 or October 1, then the interest payable on such
date shall be paid to the holders of record of the Notes on the next preceding
March 15 or September 15, respectively.

     Upon presentation of any Note redeemed in part only, the Company shall
execute and, upon the Company's written direction to the Trustee, the Trustee
shall authenticate and deliver to the holder thereof, at the expense of the
Company, a new Note or Notes, of authorized denominations, in principal amount
equal to the unredeemed portion of the Notes so presented.

          (b) On or before the tenth day after the occurrence of a Fundamental
Change, the Company, or, at its written request (which must be received by the
Trustee at least five (5) Business Days prior to the date the Trustee is
requested to give notice as described below, unless the Trustee shall agree to a
shorter period), the Trustee in the name of and at the expense of the Company,
shall mail or cause to be mailed to all holders of record on the date of the
Fundamental Change a notice (the "Company Notice") of the occurrence of such
Fundamental Change and of the redemption right at the option of the holders
arising as a result thereof.  Such notice shall be mailed in the manner and with
the effect set forth in the first paragraph of Section 3.2 (without regard for
the time limits set forth therein).  If the Company shall give such notice, the
Company shall also deliver a copy of the Company Notice to the Trustee at such
time as it is mailed to Noteholders.

     Each Company Notice shall specify the circumstances constituting the
Fundamental Change, the Repurchase Date, the price at which the Company shall be
obligated to redeem Notes, that the holder must exercise the redemption right on
or prior to the close of business on the Repurchase Date (the "Fundamental
Change Expiration Time"), that the holder shall have the right to withdraw any
Notes surrendered prior to the Fundamental Change Expiration Time, a description
of the procedure which a Noteholder must follow to exercise such redemption
right and to withdraw any surrendered Notes, the place or places where the
holder is to surrender such holder's Notes, and the amount of interest accrued
on each Note to the Repurchase Date.


                                     -22-
<PAGE>
 
     No failure of the Company to give the foregoing notices and no defect
therein shall limit the Noteholders' redemption rights or affect the validity of
the proceedings for the repurchase of the Notes pursuant to this Section 3.5.

          (c) For a Note to be so repaid at the option of the holder, the
Company must receive at the office or agency of the Company maintained for that
purpose or, at the option of such holder, the Corporate Trust Office, such Note
with the form entitled "Option to Elect Repayment Upon A Fundamental Change" on
the reverse thereof duly completed, together with such Notes duly endorsed for
transfer, on or before the Fundamental Change Expiration Time. All questions as
to the validity, eligibility (including time of receipt) and acceptance of any
Note for repayment shall be determined by the Company, whose determination shall
be final and binding absent manifest error.

          (d) On or prior to the Repurchase Date, the Company will deposit with
the Trustee or with one or more paying agents (or, if the Company is acting as
its own paying agent, set aside, segregate and hold in trust as provided in
Section 5.4) an amount of money sufficient to repay on the Repurchase Date all
the Notes to be repaid on such date at the appropriate redemption price,
together with accrued interest to (but excluding) the Repurchase Date; provided
that if such payment is made on the Repurchase Date it must be received by the
Trustee or paying agent, as the case may be, by 10:00 a.m. New York City time,
on such date. Payment for Notes surrendered for redemption (and not withdrawn)
prior to the Fundamental Change Expiration Time will be made promptly (but in no
event more than five (5) Business Days) following the Repurchase Date by mailing
checks for the amount payable to the holders of such Notes entitled thereto as
they shall appear on the registry books of the Company.

          (e) In the case of a reclassification, change, consolidation, merger,
combination, sale or conveyance to which Section 15.6 applies, in which the
Common Stock of the Company is changed or exchanged as a result into the right
to receive stock, securities or other property or assets (including cash), which
includes shares of Common Stock of the Company or another Person that are, or
upon issuance will be, traded on a United States national securities exchange or
approved for trading on an established automated over-the-counter trading market
in the United States and such shares constitute at the time such change or
exchange becomes effective in excess of 50% of the aggregate fair market value
of such stock, securities or other property or assets (including cash) (as
determined by the Company, which determination shall be conclusive and binding),
then the Person formed by such consolidation or resulting from such merger or
which acquires such assets, as the case may be, shall execute and deliver to the
Trustee a supplemental indenture (accompanied by an Opinion of Counsel that such
supplemental indenture complies with the Trust Indenture Act as in force at the
date of execution of such supplemental indenture) modifying the provisions of
this Indenture relating to the right of holders of the Notes to cause the
Company to repurchase the Notes following a Fundamental Change, including
without limitation the applicable provisions of this Section 3.5 and the
definitions of the Applicable Price, Common Stock, Fundamental Change and
Reference Market Price, as appropriate, as determined in good faith by the
Company (which determination shall be conclusive and binding), to make such
provisions apply to the common stock and the issuer thereof if different from
the Company and Common Stock of the Company (in lieu of the Company and the
Common Stock of the Company).


                                     -23-
<PAGE>
 
          (f) The Company will comply with the provisions of Rule 13e-4 and any
other tender offer rules under the Exchange Act to the extent then applicable in
connection with the redemption rights of the holders of Notes in the event of a
Fundamental Change.


                                  ARTICLE IV

                            SUBORDINATION OF NOTES

     SECTION 4.1  AGREEMENT OF SUBORDINATION.  The Company covenants and agrees,
and each holder of Notes issued hereunder by its acceptance thereof likewise
covenants and agrees, that all Notes shall be issued subject to the provisions
of this Article IV; and each Person holding any Note, whether upon original
issue or upon registration of transfer, assignment or exchange thereof, accepts
and agrees to be bound by such provisions.

     The payment of the principal of, premium, if any, and interest (including
Liquidated Damages Amount, if any) on all Notes (including, but not limited to,
the redemption price with respect to the Notes called for redemption in
accordance with Section 3.2 or submitted for redemption in accordance with
Section 3.5, as the case may be, as provided in this Indenture) issued hereunder
shall, to the extent and in the manner hereinafter set forth, be subordinated
and subject in right of payment to the prior payment in full in cash or other
payment satisfactory to the holders of Senior Indebtedness of all Senior
Indebtedness, whether outstanding at the date of this Indenture or thereafter
incurred.

     No provision of this Article IV shall prevent the occurrence of any default
or Event of Default hereunder.

     SECTION 4.2  PAYMENTS TO NOTEHOLDERS. No payment shall be made with respect
to the principal of, premium, if any, or interest (including Liquidated Damages
Amount, if any) on the Notes (including, but not limited to, the redemption
price with respect to the Notes to be called for redemption in accordance with
Section 3.2 or submitted for redemption in accordance with Section 3.5, as the
case may be, as provided in this Indenture), except payments and distributions
made by the Trustee as permitted by the first or second paragraph of Section
4.5, if:

          (i) a default in the payment of principal, premium, if any, interest,
rent or other obligations in respect of Designated Senior Indebtedness occurs
and is continuing (a "Payment Default"), unless and until such Payment Default
shall have been cured or waived or shall have ceased to exist; or

          (ii) a default, other than a Payment Default, on any Designated Senior
Indebtedness occurs and is continuing that then permits holders of such
Designated Senior Indebtedness to accelerate its maturity and the Trustee
receives a notice of the default (a "Payment Blockage Notice") from a holder of
Designated Senior Indebtedness, a Representative of Designated Senior
Indebtedness or the Company (a "Non-Payment Default").


                                     -24-
<PAGE>
 
     If the Trustee receives any Payment Blockage Notice pursuant to clause (ii)
above, no subsequent Payment Blockage Notice shall be effective for purposes of
this Section 4.2 unless and until (A) at least 365 days shall have elapsed since
the initial effectiveness of the immediately prior Payment Blockage Notice and
(B) all scheduled payments of principal, premium, if any, and interest
(including Liquidated Damages Amount, if any) on the Notes that have come due
have been paid in full in cash.  No Non-Payment Default that existed or was
continuing on the date of delivery of any Payment Blockage Notice to the Trustee
shall be, or be made, the basis for a subsequent Payment Blockage Notice, unless
such Non-Payment Default is based upon facts or events arising after the date of
delivery of such Payment Blockage Notice.

     The Company may and shall resume payments on and distributions in respect
of the Notes upon:

         (1)  in the case of a Payment Default, the date upon which any such
              Payment Default is cured or waived or ceases to exist, or

         (2)  in the case of a Non-Payment Default, the earlier of (a) the date
              upon which such default is cured or waived or ceases to exist or
              (b) 179 days after notice is received if the maturity of such
              Designated Senior Indebtedness has not been accelerated and no
              Payment Default with respect to any Designated Senior Indebtedness
              has occurred which has not been cured or waived (in which case
              clause (1) shall be applicable),

unless this Article IV otherwise prohibits the payment or distribution at the
time of such payment or distribution.

     Upon any payment by the Company, or distribution of assets of the Company
of any kind or character, whether in cash, property or securities, to creditors
upon any dissolution or winding up or liquidation or reorganization of the
Company, whether voluntary or involuntary or in bankruptcy, insolvency,
receivership or other proceedings, all amounts due or to become due upon all
Senior Indebtedness shall first be paid in full in cash or other payment
satisfactory to the holders of such Senior Indebtedness, or payment thereof in
accordance with its terms provided for in cash or other payment satisfactory to
the holders of such Senior Indebtedness before any payment is made on account of
the principal of, premium, if any, or interest (including Liquidated Damages
Amount, if any) on the Notes (except payments made pursuant to Article XIII from
monies deposited with the Trustee pursuant thereto prior to commencement of
proceedings for such dissolution, winding up, liquidation or reorganization);
and upon any such dissolution or winding up or liquidation or reorganization of
the Company or bankruptcy, insolvency, receivership or other proceeding, any
payment by the Company, or distribution of assets of the Company of any kind or
character, whether in cash, property or securities, to which the holders of the
Notes or the Trustee would be entitled, except for the provision of this Article
IV, shall (except as aforesaid) be paid by the Company or by any receiver,
trustee in bankruptcy, liquidating trustee, agent or other Person making such
payment or distribution, or by the holders of the Notes or by the Trustee under
this Indenture if received by them or it, directly to the holders of Senior
Indebtedness (pro rata to such holders on the basis of the respective amounts of
Senior Indebtedness held by such holders, or as otherwise required by law or a
court order) or their Representative or Representatives, or

                                     -25-
<PAGE>
 
to the trustee or trustees under any indenture pursuant to which any instruments
evidencing any Senior Indebtedness may have been issued, as their respective
interests may appear, to the extent necessary to pay all Senior Indebtedness in
full in cash or other payment satisfactory to the holders of such Senior
Indebtedness, after giving effect to any concurrent payment or distribution to
or for the holders of Senior Indebtedness, before any payment or distribution is
made to the holders of the Notes or to the Trustee.

     For purposes of this Article IV, the words, "cash, property or securities"
shall not be deemed to include shares of stock of the Company as reorganized or
readjusted, or securities of the Company or any other corporation provided for
by a plan of reorganization or readjustment, the payment of which is
subordinated at least to the extent provided in this Article IV with respect to
the Notes to the payment of all Senior Indebtedness which may at the time be
outstanding; provided that (i) the Senior Indebtedness is assumed by the new
corporation, if any, resulting from any reorganization or readjustment, and (ii)
the rights of the holders of Senior Indebtedness (other than leases which are
not assumed by the Company or the new corporation, as the case may be) are not,
without the consent of such holders, altered by such reorganization or
readjustment.  The consolidation of the Company with, or the merger of the
Company into, another Person or the liquidation or dissolution of the Company
following the conveyance or transfer of its property as an entirety, or
substantially as an entirety, to another Person upon the terms and conditions
provided for in Article XII shall not be deemed a dissolution, winding-up,
liquidation or reorganization for the purposes of this Section 4.2 if such other
Person shall, as a part of such consolidation, merger, conveyance or transfer,
comply with the conditions stated in Article XII.

     In the event of the acceleration of the Notes because of an Event of
Default, no payment or distribution shall be made to the Trustee or any holder
of Notes in respect of the principal of, premium, if any, or interest (including
Liquidated Damages Amount, if any) on the Notes (including, but not limited to,
the redemption price with respect to the Notes called for redemption in
accordance with Section 3.2 or submitted for redemption at the option of the
holder in accordance with Section 3.5, as the case may be, as provided in the
Indenture), except payments and distributions made by the Trustee as permitted
by the first or second paragraph of Section 4.5, until all Senior Indebtedness
has been paid in full in cash or other payment satisfactory to the holders of
Senior Indebtedness or such acceleration is rescinded in accordance with the
terms of this Indenture.  If payment of the Notes is accelerated because of an
Event of Default, the Company or the Trustee shall promptly notify holders of
Designated Senior Indebtedness of the acceleration.

     In the event that, notwithstanding the foregoing provisions, any payment or
distribution of assets of the Company of any kind or character, whether in cash,
property or securities (including, without limitation, by way of setoff or
otherwise), prohibited by the foregoing provisions in this Section 4.2, shall be
received by the Trustee or the holders of the Notes before all Senior
Indebtedness is paid in full in cash or other payment satisfactory to the
holders of such Senior Indebtedness, or provision is made for such payment
thereof in accordance with its terms in cash or other payment satisfactory to
the holders of such Senior Indebtedness, such payment or distribution shall be
held in trust for the benefit of and shall be paid over or delivered to the
holders of Senior Indebtedness or their representative or representatives, or to
the trustee or trustees under any indenture pursuant to which any instruments
evidencing any Senior Indebtedness may have been issued, as their respective
interests may appear, as

                                     -26-
<PAGE>
 
calculated by the Company, for application to the payment of any Senior
Indebtedness remaining unpaid to the extent necessary to pay all Senior
Indebtedness in full in cash or other payment satisfactory to the holders of
such Senior Indebtedness, after giving effect to any concurrent payment or
distribution to or for the holders of such Senior Indebtedness.

     Nothing in this Section 4.2 shall apply to claims of, or payments to, the
Trustee under or pursuant to Section 8.6.  This Section 4.2 shall be subject to
the further provisions of Section 4.5.

     SECTION 4.3   SUBROGATION OF NOTES.  Subject to the payment in full of all
Senior Indebtedness, the rights of the holders of the Notes shall be subrogated
to the extent of the payments or distributions made to the holders of such
Senior Indebtedness pursuant to the provisions of this Article IV (equally and
ratably with the holders of all indebtedness of the Company which by its express
terms is subordinated to other indebtedness of the Company to substantially the
same extent as the Notes are subordinated and is entitled to like rights of
subrogation) to the rights of the holders of Senior Indebtedness to receive
payments or distributions of cash, property or securities of the Company
applicable to the Senior Indebtedness until the principal, premium, if any, and
interest (including Liquidated Damages Amount, if any) on the Notes shall be
paid in full; and, for the purposes of such subrogation, no payments or
distributions to the holders of the Senior Indebtedness of any cash, property or
securities to which the holders of the Notes or the Trustee would be entitled
except for the provisions of this Article IV, and no payment over pursuant to
the provisions of this Article IV, to or for the benefit of the holders of
Senior Indebtedness by holders of the Notes or the Trustee, shall, as between
the Company, its creditors other than holders of Senior Indebtedness, and the
holders of the Notes, be deemed to be a payment by the Company to or on account
of the Senior Indebtedness; and no payments or distributions of cash, property
or securities to or for the benefit of the holders of the Notes pursuant to the
subrogation provisions of this Article IV, which would otherwise have been paid
to the holders of Senior Indebtedness shall be deemed to be a payment by the
Company to or for the account of the Notes.  It is understood that the
provisions of this Article IV are and are intended solely for the purposes of
defining the relative rights of the holders of the Notes, on the one hand, and
the holders of the Senior Indebtedness, on the other hand.

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

     Upon any payment or distribution of assets of the Company referred to in
this Article IV, the Trustee, subject to the provisions of Section 8.1, and the
holders of the Notes shall be entitled to rely

                                     -27-
<PAGE>
 
upon any order or decree made by any court of competent jurisdiction in which
such bankruptcy, dissolution, winding up, liquidation or reorganization
proceedings are pending, or a certificate of the receiver, trustee in
bankruptcy, liquidating trustee, agent or other Person making such payment or
distribution, delivered to the Trustee or to the holders of the Notes, for the
purpose of ascertaining the Persons entitled to participate in such
distribution, the holders of the Senior Indebtedness and other indebtedness of
the Company, the amount thereof or payable thereon and all other facts pertinent
thereto or to this Article IV.

     SECTION 4.4   AUTHORIZATION TO EFFECT SUBORDINATION.  Each holder of a
Note by the holder's acceptance thereof authorizes and directs the Trustee on
the holder's behalf to take such action as may be necessary or appropriate to
effectuate the subordination as provided in this Article IV and appoints the
Trustee to act as the holder's attorney-in-fact for any and all such purposes.
If the Trustee does not file a proper proof of claim or proof of debt in the
form required in any proceeding referred to in the third paragraph of Section
7.2 hereof at least thirty (30) days before the expiration of the time to file
such claim, the holders of any Senior Indebtedness or their representatives are
hereby authorized to file an appropriate claim for and on behalf of the holders
of the Notes.

     SECTION 4.5   NOTICE TO TRUSTEE.  The Company shall give prompt written
notice in the form of an Officers' Certificate to a Responsible Officer of the
Trustee and to any paying agent of any fact known to the Company which would
prohibit the making of any payment of monies to or by the Trustee or any paying
agent in respect of the Notes pursuant to the provisions of this Article IV.
Notwithstanding the provisions of this Article IV or any other provision of this
Indenture, the Trustee shall not be charged with knowledge of the existence of
any facts which would prohibit the making of any payment of monies to or by the
Trustee in respect of the Notes pursuant to the provisions of this Article IV,
unless and until a Responsible Officer of the Trustee shall have received
written notice thereof at the Corporate Trust Office from the Company (in the
form of an Officers' Certificate) or a Representative or a holder or holders of
Senior Indebtedness or from any trustee thereof; and before the receipt of any
such written notice, the Trustee, subject to the provisions of Section 8.1,
shall be entitled in all respects to assume that no such facts exist; provided
that if on a date not  less than two Business Days prior to the date upon which
by the terms hereof any such monies may become payable for any purpose
(including, without limitation, the payment of the principal of, or premium, if
any, or interest (including Liquidated Damages Amount, if any) on any Note) the
Trustee shall not have received, with respect to such monies, the notice
provided for in this Section 4.5, then, anything herein contained to the
contrary notwithstanding, the Trustee shall have full power and authority to
apply moneys received to the purpose for which they were received, and shall not
be affected by any notice to the contrary which may be received by it on or
after such prior date.

     Notwithstanding anything in this Article IV to the contrary, nothing shall
prevent any payment by the Trustee to the Noteholders of monies deposited with
it pursuant to Section 13.1, and any such payment shall not be subject to the
provisions of Section 4.1 or 4.2.

     The Trustee, subject to the provisions of Section 8.1, shall be entitled to
rely on the delivery to it of a written notice by a Representative or a person
representing himself to be a holder of Senior Indebtedness (or a trustee on
behalf of such holder) to establish that such notice has been given by a

                                     -28-
<PAGE>
 
Representative or a holder of Senior Indebtedness or a trustee on behalf of any
such holder or holders.  The Trustee shall not be required to make any payment
or distribution to or on behalf of a holder of Senior Indebtedness pursuant to
this Article IV unless it has received satisfactory evidence as to the amount of
Senior Indebtedness held by such Person, the extent to which such Person is
entitled to participate in such payment or distribution and any other facts
pertinent to the rights of such Person under this Article IV.

     SECTION 4.6    TRUSTEE'S RELATION TO SENIOR INDEBTEDNESS.  The Trustee in
its individual capacity shall be entitled to all the rights set forth in this
Article IV in respect of any Senior Indebtedness at any time held by it, to the
same extent as any other holder of Senior Indebtedness, and nothing in Section
8.13 or elsewhere in this Indenture shall deprive the Trustee of any of its
rights as such holder.

     With respect to the holders of Senior Indebtedness, the Trustee undertakes
to perform or to observe only such of its covenants and obligations as are
specifically set forth in this Article IV, and no implied covenants or
obligations with respect to the holders of Senior Indebtedness shall be read
into this Indenture against the Trustee.  The Trustee shall not be deemed to owe
any fiduciary duty to the holders of Senior Indebtedness and, subject to the
provisions of Section 8.1, the Trustee shall not be liable to any holder of
Senior Indebtedness (i) for any failure to make any payments or distributions to
such holder or (ii) if it shall pay over or deliver to holders of Notes, the
Company or any other Person money or assets to which any holder of Senior
Indebtedness shall be entitled by virtue of this Article IV or otherwise.

     SECTION 4.7    NO IMPAIRMENT OF SUBORDINATION.  No right of any present or
future holder of any Senior Indebtedness to enforce subordination as herein
provided shall at any time in any way be prejudiced or impaired by any act or
failure to act on the part of the Company or by any act or failure to act, in
good faith, by any such holder, or by any noncompliance by the Company with the
terms, provisions and covenants of this Indenture, regardless of any knowledge
thereof which any such holder may have or otherwise be charged with.

     SECTION 4.8   CERTAIN CONVERSIONS NOT DEEMED PAYMENT.  For the purposes of
this Article IV only, (1) the issuance and delivery of junior securities upon
conversion of Notes in accordance with Article XV shall not be deemed to
constitute a payment or distribution on account of the principal of, premium, if
any, or interest (including Liquidated Damages Amount, if any) on Notes or on
account of the purchase or other acquisition of Notes, and (2) the payment,
issuance or delivery of cash (except in satisfaction of fractional shares
pursuant to Section 15.3), property or securities (other than junior securities)
upon conversion of a Note shall be deemed to constitute payment on account of
the principal of, premium, if any, or interest (including Liquidated Damages
Amount, if any) on such Note.  For the purposes of this Section 4.8, the term
"junior securities" means (a) shares of any stock of any class of the Company or
(b) securities of the Company that are subordinated in right of payment to all
Senior Indebtedness that may be outstanding at the time of issuance or delivery
of such securities to substantially the same extent as, or to a greater extent
than, the Notes are so subordinated as provided in this Article.  Nothing
contained in this Article IV or elsewhere in this Indenture or in the Notes is
intended to or shall impair, as among the Company, its creditors (other than
holders of Senior

                                     -29-
<PAGE>
 
Indebtedness) and the Noteholders, the right, which is absolute and
unconditional, of the Holder of any Note to convert such Note in accordance with
Article XV.
    
     SECTION 4.9    ARTICLE APPLICABLE TO PAYING AGENTS.  If at any time any
paying agent other than the Trustee shall have been appointed by the Company and
be then acting hereunder, the term "Trustee" as used in this Article shall
(unless the context otherwise requires) be construed as extending to and
including such paying agent within its meaning as fully for all intents and
purposes as if such paying agent were named in this Article in addition to or in
place of the Trustee; provided, however, that the first paragraph of Section 4.5
shall not apply to the Company or any Affiliate of the Company if it or such
Affiliate acts as paying agent.      

     The Trustee shall not be responsible for the actions or inactions of any
other paying agents (including the Company if acting as its own paying agent)
and shall have no control of any funds held by such other paying agents.

     SECTION 4.10   SENIOR INDEBTEDNESS ENTITLED TO RELY.  The holders of Senior
Indebtedness (including, without limitation, Designated Senior Indebtedness)
shall have the right to rely upon this Article IV, and no amendment or
modification of the provisions contained herein shall diminish the rights of
such holders unless such holders shall have agreed in writing thereto.

     SECTION 4.11   RELIANCE ON JUDICIAL ORDER OR CERTIFICATE OF LIQUIDATING
AGENT.  Upon any payment or distribution of assets of the Company referred to in
this Article, the Trustee and the Noteholders shall be entitled to rely upon any
order or decree entered by any court of competent jurisdiction in which such
insolvency, bankruptcy, receivership, liquidation, reorganization, dissolution,
winding up or similar case or proceeding is pending, or a certificate of the
trustee in bankruptcy, liquidating trustee, custodian, receiver, assignee for
the benefit of creditors, agent or other Person making such payment or
distribution, delivered to the Trustee or to the Noteholders, for the purpose of
ascertaining the Persons entitled to participate in such payment or
distribution, the holders of Senior Indebtedness and other indebtedness of the
Company, the amount thereof or payable thereon, the amount or amounts paid or
distributed thereon and all other facts pertinent thereto or to this Article.

                                   ARTICLE V

                      PARTICULAR COVENANTS OF THE COMPANY

     SECTION 5.1    PAYMENT OF PRINCIPAL, PREMIUM AND INTEREST.  The Company
covenants and agrees that it will duly and punctually pay or cause to be paid
the principal of and premium, if any (including upon redemption pursuant to
Article III), and interest (including Liquidated Damages Amount, if any) on each
of the Notes at the places, at the respective times and in the manner provided
herein and in the Notes.

     SECTION 5.2    MAINTENANCE OF OFFICE OR AGENCY.  The Company will maintain
an office or agency in The Borough of Manhattan, The City of New York, an office
or agency where the Notes may be surrendered for registration of transfer or
exchange or for presentation for payment or for conversion or redemption and
where notices and demands to or upon the Company in respect of the Notes and
this

                                     -30-
<PAGE>
 
Indenture may be served.  The Company will give prompt written notice to the
Trustee of the location, and any change in the location, of such office or
agency not designated or appointed by the Trustee.  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 in The Borough of Manhattan, The City of New York.

     The Company may also from time to time designate co-registrars and one or
more other offices or agencies where the Notes may be presented or surrendered
for any or all such purposes and may from time to time rescind such
designations.  The Company will give prompt written notice of any such
designation or rescission and of any change in the location of any such other
office or agency.

     The Company hereby initially designates the Trustee as paying agent, Note
registrar, Custodian and conversion agent and the Corporate Trust Office of the
Trustee in The Borough of Manhattan, The City of New York as the office or
agency of the Company for each of the aforesaid purposes.

     So long as the Trustee is the Note registrar, the Trustee agrees to mail,
or cause to be mailed, the notices set forth in Section 8.10(a) and the third
paragraph of Section 8.11.  If co-registrars have been appointed in accordance
with this Section, the Trustee shall mail such notices only to the Company and
the holders of Notes it can identify from its records.

     SECTION 5.3    APPOINTMENTS TO FILL VACANCIES IN TRUSTEE'S OFFICE.  The
Company, whenever necessary to avoid or fill a vacancy in the office of Trustee,
will appoint, in the manner provided in Section 8.10, a Trustee, so that there
shall at all times be a Trustee hereunder.

     SECTION 5.4    PROVISIONS AS TO PAYING AGENT.

          (a) If the Company shall appoint a paying agent other than the
Trustee, or if the Trustee shall appoint such a paying agent, it will cause such
paying agent to execute and deliver to the Trustee an instrument in which such
agent shall agree with the Trustee, subject to the provisions of this Section
5.4:

                (1) that it will hold all sums held by it as such agent for the
payment of the principal of and premium, if any, or interest on the Notes
(whether such sums have been paid to it by the Company or by any other obligor
on the Notes) in trust for the benefit of the holders of the Notes;

                (2) that it will give the Trustee notice of any failure by the
Company (or by any other obligor on the Notes) to make any payment of the
principal of and premium, if any, or interest on the Notes when the same shall
be due and payable; and

                (3) that at any time during the continuance of an Event of
Default, upon request of the Trustee, it will forthwith pay to the Trustee all
sums so held in trust.

                                     -31-
<PAGE>
 
     The Company shall, on or before each due date of the principal of, premium,
if any, or interest on the Notes, deposit with the paying agent a sum sufficient
to pay such principal, premium, if any, or interest, and (unless such paying
agent is the Trustee) the Company will promptly notify the Trustee of any
failure to take such action; provided that if such deposit is made on the due
date, such deposit shall be received by the paying agent by 10:00 a.m. New York
City time, on such date.

          (b) If the Company shall act as its own paying agent, it will, on or
before each due date of the principal of, premium, if any, or interest
(including Liquidated Damages Amount, if any) on the Notes, set aside, segregate
and hold in trust for the benefit of the holders of the Notes a sum sufficient
to pay such principal, premium, if any, or interest (including Liquidated
Damages Amount, if any) so becoming due and will notify the Trustee of any
failure to take such action and of any failure by the Company (or any other
obligor under the Notes) to make any payment of the principal of, premium, if
any, or interest (including Liquidated Damages Amount, if any) on the Notes when
the same shall become due and payable.

          (c) Anything in this Section 5.4 to the contrary notwithstanding, the
Company may, at any time, for the purpose of obtaining a satisfaction and
discharge of this Indenture, or for any other reason, pay or cause to be paid to
the Trustee all sums held in trust by the Company or any paying agent hereunder
as required by this Section 5.4, such sums to be held by the Trustee upon the
trusts herein contained and upon such payment by the Company or any paying agent
to the Trustee, the Company or such paying agent shall be released from all
further liability with respect to such sums.

          (d) Anything in this Section 5.4 to the contrary notwithstanding, the
agreement to hold sums in trust as provided in this Section 5.4 is subject to
Sections 13.3 and 13.4.

          The Trustee shall not be responsible for the actions of any other
paying agents (including the Company if acting as its own paying agent) and
shall have no control of any funds held by such other paying agents.

     SECTION 5.5    EXISTENCE.  Subject to Article XII, the Company will do or
cause to be done all things necessary to preserve and keep in full force and
effect its existence and rights (charter and statutory); provided, however, that
the Company shall not be required to preserve any such right if the Company
shall determine that the preservation thereof is no longer desirable in the
conduct of the business of the Company and that the loss thereof is not
disadvantageous in any material respect to the holders.

     SECTION 5.6    MAINTENANCE OF PROPERTIES.  The Company will cause all
properties used or useful in the conduct of its business or the business of any
Significant Subsidiary to be maintained and kept in good condition, repair and
working order and supplied with all necessary equipment and will cause to be
made all necessary repairs, renewals, replacements, betterments and improvements
thereof, all as in the judgment of the Company may be necessary so that the
business carried on in connection therewith may be properly and advantageously
conducted at all times; provided, however, that nothing in this Section shall
prevent the Company from discontinuing the operation or maintenance of any of
such properties if such discontinuance is, in the judgment of the Company,
desirable in the conduct of

                                     -32-
<PAGE>
 
its business or the business of any Significant Subsidiary and not
disadvantageous in any material respect to the holders.

     SECTION 5.7    PAYMENT OF TAXES AND OTHER CLAIMS.  The Company will pay or
discharge, or cause to be paid or discharged, before the same may become
delinquent, (i) all taxes, assessments and governmental charges levied or
imposed upon the Company or any Significant Subsidiary or upon the income,
profits or property of the Company or any Significant Subsidiary, (ii) all
claims for labor, materials and supplies which, if unpaid, might by law become a
lien or charge upon the property of the Company or any Significant Subsidiary
and (iii) all stamps and other duties, if any, which may be imposed by the
United States or any political subdivision thereof or therein in connection with
the issuance, transfer, exchange or conversion of any Notes or with respect to
this Indenture; provided, however, that, in the case of clauses (i) and (ii),
the Company shall not be required to pay or discharge or cause to be paid or
discharged any such tax, assessment, charge or claim (A) if the failure to do so
will not, in the aggregate, have a material adverse impact on the Company, or
(B) if the amount, applicability or validity is being contested in good faith by
appropriate proceedings.

     SECTION 5.8    RULE 144A INFORMATION REQUIREMENT.  Within the period prior
to the expiration of the holding period applicable to sales thereof under Rule
144(k) under the Securities Act (or any successor provision), the Company
covenants and agrees that it shall, during any period in which it is not subject
to Section 13 or 15(d) under the Exchange Act, make available to any holder or
beneficial holder of Notes or any Common Stock issued upon conversion thereof
which continue to be Restricted Securities in connection with any sale thereof
and any prospective purchaser of Notes or such Common Stock from such holder or
beneficial holder, the information required pursuant to Rule 144A(d)(4) under
the Securities Act upon the request of any holder or beneficial holder of the
Notes or such Common Stock and it will take such further action as any holder or
beneficial holder of such Notes or such Common Stock may reasonably request, all
to the extent required from time to time to enable such holder or beneficial
holder to sell its Notes or Common Stock without registration under the
Securities Act within the limitation of the exemption provided by Rule 144A, as
such Rule may be amended from time to time.  Upon the request of any holder or
any beneficial holder of the Notes or such Common Stock, the Company will
deliver to such holder a written statement as to whether it has complied with
such requirements.

     SECTION 5.9    STAY, EXTENSION AND USURY LAWS.  The Company covenants (to
the extent that it may lawfully do so) that it shall not at any time insist
upon, plead, or in any manner whatsoever claim or take the benefit or advantage
of, any stay, extension or usury law or other law which would prohibit or
forgive the Company from paying all or any portion of the principal of, premium,
if any, or interest (including Liquidated Damages Amount, if any) on the Notes
as contemplated herein, wherever enacted, now or at any time hereafter in force,
or which may affect the covenants or the performance of this Indenture and the
Company (to the extent it may lawfully do so) hereby expressly waives all
benefit or advantage of any such law, and covenants that it will not, by resort
to any such law, hinder, delay or impede the execution of any power herein
granted to the Trustee, but will suffer and permit the execution of every such
power as though no such law has been enacted.


                                     -33-
<PAGE>
 
     SECTION 5.10    COMPLIANCE CERTIFICATE.  The Company shall deliver to the
Trustee, within one hundred twenty (120) days after the end of each fiscal year
of the Company, a certificate signed by either the principal executive officer,
principal financial officer or principal accounting officer of the Company,
stating whether or not to the best knowledge of the signer thereof the Company
is in default in the performance and observance of any of the terms, provisions
and conditions of this Indenture (without regard to any period of grace or
requirement of notice provided hereunder) and, if the Company shall be in
default, specifying all such defaults and the nature and status thereof of which
the signer may have knowledge.

     The Company will deliver to the Trustee, forthwith upon becoming aware of
any default in the performance or observance of any covenant, agreement or
condition contained in this Indenture, or any Event of Default, an Officers'
Certificate specifying with particularity such default or Event of Default and
further stating what action the Company has taken, is taking or proposes to take
with respect thereto.

     Any notice required to be given under this Section 5.10 shall be delivered
to the Trustee at its Corporate Trust Office.


                                   ARTICLE V

         NOTEHOLDERS' LISTS AND REPORTS BY THE COMPANY AND THE TRUSTEE

     SECTION 6.1    NOTEHOLDERS' LISTS.  The Company covenants and agrees that
it will furnish or cause to be furnished to the Trustee, semiannually, not more
than fifteen (15) days after each March 15 and September 15 in each year
beginning with September 15, 1998, and at such other times as the Trustee may
request in writing, within thirty (30) days after receipt by the Company of any
such request (or such lesser time as the Trustee may reasonably request in order
to enable it to timely provide any notice to be provided by it hereunder), a
list in such form as the Trustee may reasonably require of the names and
addresses of the holders of Notes as of a date not more than fifteen (15) days
(or such other date as the Trustee may reasonably request in order to so provide
any such notices) prior to the time such information is furnished, except that
no such list need be furnished by the Company to the Trustee so long as the
Trustee is acting as the sole Note registrar.

     SECTION 6.2    PRESERVATION AND DISCLOSURE OF LISTS.

          (a) The Trustee shall preserve, in as current a form as is reasonably
practicable, all information as to the names and addresses of the holders of
Notes contained in the most recent list furnished to it as provided in Section
6.1 or maintained by the Trustee in its capacity as Note registrar or co-
registrar in respect of the Notes, if so acting.  The Trustee may destroy any
list furnished to it as provided in Section 6.1 upon receipt of a new list so
furnished.

          (b) The rights of Noteholders to communicate with other holders of
Notes with respect to their rights under this Indenture or under the Notes, and
the corresponding rights and duties of the Trustee, shall be as provided by the
Trust Indenture Act.

                                     -34-
<PAGE>
 
          (c) Every Noteholder, by receiving and holding the same, agrees with
the Company and the Trustee that neither the Company nor the Trustee nor any
agent of either of them shall be held accountable by reason of any disclosure of
information as to names and addresses of holders of Notes made pursuant to the
Trust Indenture Act.

     SECTION 6.3    REPORTS BY TRUSTEE.

          (a) Within sixty (60) days after May 15 of each year commencing with
the year 1998, the Trustee shall transmit to holders of Notes such reports dated
as of May 15 of the year in which such reports are made concerning the Trustee
and its actions under this Indenture as may be required pursuant to the Trust
Indenture Act at the times and in the manner provided pursuant thereto.

          (b) A copy of such report shall, at the time of such transmission to
holders of Notes, be filed by the Trustee with each stock exchange and automated
quotation system upon which the Notes are listed and with the Company.  The
Company will notify the Trustee in writing within a reasonable time when the
Notes are listed on any stock exchange or automated quotation system.

     SECTION 6.4    REPORTS BY COMPANY.  The Company shall file with the Trustee
(and the Commission if at any time after the Indenture becomes qualified under
the Trust Indenture Act), and transmit to holders of Notes, such information,
documents and other reports and such summaries thereof, as may be required
pursuant to the Trust Indenture Act at the times and in the manner provided
pursuant to such Act, whether or not the Notes are governed by such Act;
provided that any such information, documents or reports required to be filed
with the Commission pursuant to Section 13 or 15(d) of the Exchange Act shall be
filed with the Trustee within fifteen (15) days after the same is so required to
be filed with the Commission.  Delivery of such reports, information and
documents to the Trustee is for informational purposes only and the Trustee's
receipt of such shall not constitute constructive notice of any information
contained therein or determinable from information contained therein, including
the Company's compliance with any of its covenants hereunder (as to which the
Trustee is entitled to rely exclusively on Officers' Certificates).


                                  ARTICLE VII

        REMEDIES OF THE TRUSTEE AND NOTEHOLDERS ON AN EVENT OF DEFAULT

     SECTION 7.1    EVENTS OF DEFAULT.  In case one or more of the following
Events of Default (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) shall have occurred and be
continuing:

          (a) default in the payment of any installment of interest (including
Liquidated Damages Amount, if any) upon any of the Notes as and when the same
shall become due and payable, and continuance of such default for a period of
thirty (30) days, whether or not such payment is permitted under Article IV
hereof; or


                                     -35-
<PAGE>
 
          (b) default in the payment of the principal of or premium, if any, on
any of the Notes as and when the same shall become due and payable either at
maturity or in connection with any redemption pursuant to Article III, by
acceleration or otherwise, whether or not such payment is permitted under
Article IV hereof; or

          (c) failure on the part of the Company duly to observe or perform any
other of the covenants or agreements on the part of the Company in the Notes or
in this Indenture (other than a covenant or agreement a default in whose
performance or whose breach is elsewhere in this Section 7.1 specifically dealt
with) continued for a period of sixty (60) days after the date on which written
notice of such failure, requiring the Company to remedy the same, shall have
been given to the Company by the Trustee, or to the Company and a Responsible
Officer of the Trustee by the holders of at least twenty-five percent (25%) in
aggregate principal amount of the Notes at the time outstanding determined in
accordance with Section 9.4; or

          (d) the Company or any Significant Subsidiary shall commence a
voluntary case or other proceeding seeking liquidation, reorganization or other
relief with respect to itself or any Significant Subsidiary or its or such
Significant Subsidiary's debts under any bankruptcy, insolvency or other similar
law now or hereafter in effect or seeking the appointment of a trustee,
receiver, liquidator, custodian or other similar official of it or any
Significant Subsidiary or any substantial part of the property of the Company or
any Significant Subsidiary, or shall consent to any such relief or to the
appointment of or taking possession by any such official in an involuntary case
or other proceeding commenced against it or any Significant Subsidiary, or shall
make a general assignment for the benefit of creditors, or shall fail generally
to pay its debts as they become due; or

          (e) an involuntary case or other proceeding shall be commenced against
the Company or any Significant Subsidiary seeking liquidation, reorganization or
other relief with respect to it or any Significant Subsidiary or its or such
Significant Subsidiary's debts under any bankruptcy, insolvency or other similar
law now or hereafter in effect or seeking the appointment of a trustee,
receiver, liquidator, custodian or other similar official of it or any
Significant Subsidiary or any substantial part of the property of the Company or
any Significant Subsidiary, and such involuntary case or other proceeding shall
remain undismissed and unstayed for a period of ninety (90) consecutive days;

then, and in each and every such case (other than an Event of Default specified
in Section 7.1 (d) or (e) with respect to the Company), unless the principal of
all of the Notes shall have already become due and payable, either the Trustee
or the holders of not less than twenty-five percent (25%) in aggregate principal
amount of the Notes then outstanding hereunder determined in accordance with
Section 9.4, by notice in writing to the Company (and to the Trustee if given by
Noteholders), may declare the principal of and premium, if any, on all the Notes
and the interest accrued thereon (including Liquidated Damages Amount, if any)
to be due and payable immediately, and upon any such declaration the same shall
become and shall be immediately due and payable, anything in this Indenture or
in the Notes contained to the contrary notwithstanding.  If an Event of Default
specified in Section 7.1(d) or (e) with respect to the Company occurs, the
principal of all the Notes and the interest accrued thereon shall (including
Liquidated Damages Amount, if any) be immediately and automatically due and
payable without necessity of further action.  This provision, however, is
subject to the conditions that if, at any

                                     -36-
<PAGE>
 
time after the principal of the Notes shall have been so declared due and
payable, and before any judgment or decree for the payment of the monies due
shall have been obtained or entered as hereinafter provided, the Company shall
pay or shall deposit with the Trustee a sum sufficient to pay all matured
installments of interest upon (including Liquidated Damages Amount, if any) all
Notes and the principal of and premium, if any, on any and all Notes which shall
have become due otherwise than by acceleration (with interest on overdue
installments of interest (including Liquidated Damages Amount, if any) (to the
extent that payment of such interest is enforceable under applicable law) and on
such principal and premium, if any, at the rate borne by the Notes, to the date
of such payment or deposit) and amounts due to the Trustee pursuant to Section
8.6, and if any and all defaults under this Indenture, other than the nonpayment
of principal of and premium, if any, and accrued interest on (including
Liquidated Damages Amount, if any) Notes which shall have become due by
acceleration, shall have been cured or waived pursuant to Section 7.7 -- then
and in every such case the holders of a majority in aggregate principal amount
of the Notes then outstanding, by written notice to the Company and to the
Trustee, may waive all defaults or Events of Default and rescind and annul such
declaration and its consequences; but no such waiver or rescission and annulment
shall extend to or shall affect any subsequent default or Event of Default, or
shall impair any right consequent thereon.  The Company shall notify a
Responsible Officer of the Trustee, promptly upon becoming aware thereof, of any
Event of Default.

     In case the Trustee shall have proceeded to enforce any right under this
Indenture and such proceedings shall have been discontinued or abandoned because
of such waiver or rescission and annulment or for any other reason or shall have
been determined adversely to the Trustee, then and in every such case the
Company, the holders of Notes, and the Trustee shall be restored respectively to
their several positions and rights hereunder, and all rights, remedies and
powers of the Company, the holders of Notes, and the Trustee shall continue as
though no such proceeding had been taken.

     SECTION 7.2    PAYMENTS OF NOTES ON DEFAULT; SUIT THEREFOR.  The Company
covenants that (a) in case default shall be made in the payment of any
installment of interest upon (including Liquidated Damages Amount, if any) any
of the Notes as and when the same shall become due and payable, and such default
shall have continued for a period of thirty (30) days, or (b) in case default
shall be made in the payment of the principal of or premium, if any, on any of
the Notes as and when the same shall have become due and payable, whether at
maturity of the Notes or in connection with any redemption, by or under this
Indenture declaration or otherwise -- then, upon demand of the Trustee, the
Company will pay to the Trustee, for the benefit of the holders of the Notes,
the whole amount that then shall have become due and payable on all such Notes
for principal and premium, if any, or interest (including Liquidated Damages
Amount, if any), as the case may be, with interest upon the overdue principal
and premium, if any, and (to the extent that payment of such interest is
enforceable under applicable law) upon the overdue installments of interest
(including Liquidated Damages Amount, if any) at the rate borne by the Notes;
and, in addition thereto, such further amount as shall be sufficient to cover
the costs and expenses of collection, including reasonable compensation to the
Trustee, its agents, attorneys and counsel, and all other amounts due the
Trustee under Section 8.6.  Until such demand by the Trustee, the Company may
pay the principal of and premium, if any, and interest on (including Liquidated
Damages Amount, if any) the Notes to the registered holders, whether or not the
Notes are overdue.


                                     -37-
<PAGE>
 
     In case the Company shall fail forthwith to pay such amounts upon such
demand, the Trustee, in its own name and as trustee of an express trust, shall
be entitled and empowered to institute any actions or proceedings at law or in
equity for the collection of the sums so due and unpaid, and may prosecute any
such action or proceeding to judgment or final decree, and may enforce any such
judgment or final decree against the Company or any other obligor on the Notes
and collect in the manner provided by law out of the property of the Company or
any other obligor on the Notes wherever situated the monies adjudged or decreed
to be payable.

     In the case there shall be pending proceedings for the bankruptcy or for
the reorganization of the Company or any other obligor on the Notes under Title
11 of the United States Code, or any other applicable law, or in case a
receiver, assignee or trustee in bankruptcy or reorganization, liquidator,
sequestrator or similar official shall have been appointed for or taken
possession of the Company or such other obligor, the property of the Company or
such other obligor, or in the case of any other judicial proceedings relative to
the Company or such other obligor upon the Notes, or to the creditors or
property of the Company or such other obligor, the Trustee, irrespective of
whether the principal of the Notes shall then be due and payable as therein
expressed or by declaration or otherwise and irrespective of whether the Trustee
shall have made any demand pursuant to the provisions of this Section 7.2, shall
be entitled and empowered, by intervention in such proceedings or otherwise, to
file and prove a claim or claims for the whole amount of principal, premium, if
any, and interest (including Liquidated Damages Amount, if any) owing and unpaid
in respect of the Notes, and, in case of any judicial proceedings, to 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 of the Noteholders allowed in
such judicial proceedings relative to the Company or any other obligor on the
Notes, its or their creditors, or its or their property, and to collect and
receive any monies or other property payable or deliverable on any such claims,
and to distribute the same after the deduction of any amounts due the Trustee
under Section 8.6; and any receiver, assignee or trustee in bankruptcy or
reorganization, liquidator, custodian or similar official is hereby authorized
by each of the Noteholders to make such payments to the Trustee, and, in the
event that the Trustee shall consent to the making of such payments directly to
the Noteholders, to pay to the Trustee any amount due it for reasonable
compensation, expenses, advances and disbursements, including counsel fees
incurred by it up to the date of such distribution.  To the extent that such
payment of reasonable compensation, expenses, advances and disbursements out of
the estate in any such proceedings shall be denied for any reason, payment of
the same shall be secured by a lien on, and shall be paid out of, any and all
distributions, dividends, monies, securities and other property which the
holders of the Notes may be entitled to receive in such proceedings, whether in
liquidation or under any plan of reorganization or arrangement or otherwise.

     All rights of action and of asserting claims under this Indenture, or under
any of the Notes, may be enforced by the Trustee without the possession of any
of the Notes, or the production thereof at any trial or other proceeding
relative thereto, and any such suit or proceeding instituted by the Trustee
shall be brought in its own name as trustee of an express trust, and any
recovery of judgment shall, after provision for the payment of the reasonable
compensation, expenses, disbursements and advances of the Trustee, its agents
and counsel, be for the ratable benefit of the holders of the Notes.

                                     -38-
<PAGE>
 
     In any proceedings brought by the Trustee (and in any proceedings involving
the interpretation of any provision of this Indenture to which the Trustee shall
be a party) the Trustee shall be held to represent all the holders of the Notes,
and it shall not be necessary to make any holders of the Notes parties to any
such proceedings.

     SECTION 7.3    APPLICATION OF MONIES COLLECTED BY TRUSTEE.  Any monies
collected by the Trustee pursuant to this Article VII shall be applied in the
order following, at the date or dates fixed by the Trustee for the distribution
of such monies, upon presentation of the several Notes, and stamping thereon the
payment, if only partially paid, and upon surrender thereof, if fully paid:

          FIRST:  To the payment of all amounts due the Trustee under Section
     8.6;

          SECOND: Subject to the provisions of Article IV, in case the
     principal of the outstanding Notes shall not have become due and be unpaid,
     to the payment of interest on (including Liquidated Damages Amount, if any)
     the Notes in default in the order of the maturity of the installments of
     such interest, with interest (to the extent that such interest has been
     collected by the Trustee) upon the overdue installments of interest
     (including Liquidated Damages Amount, if any) at the rate borne by the
     Notes, such payments to be made ratably to the Persons entitled thereto;

          THIRD:  Subject to the provisions of Article IV, in case the principal
     of the outstanding Notes shall have become due, by declaration or
     otherwise, and be unpaid to the payment of the whole amount then owing and
     unpaid upon the Notes for principal and premium, if any, and interest
     (including Liquidated Damages Amount, if any), with interest on the overdue
     principal and premium, if any, and (to the extent that such interest has
     been collected by the Trustee) upon overdue installments of interest
     (including Liquidated Damages Amount, if any) at the rate borne by the
     Notes; and in case such monies shall be insufficient to pay in full the
     whole amounts so due and unpaid upon the Notes, then to the payment of such
     principal and premium, if any, and interest (including Liquidated Damages
     Amount, if any) without preference or priority of principal and premium, if
     any, over interest (including Liquidated Damages Amount, if any), or of
     interest (including Liquidated Damages Amount, if any) over principal and
     premium, if any, or of any installment of interest over any other
     installment of interest, or of any Note over any other Note, ratably to the
     aggregate of such principal and premium, if any, and accrued and unpaid
     interest; and

          FOURTH: Subject to the provisions of Article IV, to the payment of
     the remainder, if any, to the Company or any other Person lawfully entitled
     thereto.

     SECTION 7.4    PROCEEDINGS BY NOTEHOLDER.  No holder of any Note shall have
any right by virtue of or by availing of any provision of this Indenture to
institute any suit, action or proceeding in equity or at law upon or under or
with respect to this Indenture, or for the appointment of a receiver, trustee,
liquidator, custodian or other similar official, or for any other remedy
hereunder, unless such holder previously shall have given to the Trustee written
notice of an Event of Default and of the continuance thereof, as hereinbefore
provided, and unless also the holders of not less than twenty-five percent (25%)

                                     -39-
<PAGE>
 
in aggregate principal amount of the Notes then outstanding shall have made
written request upon the Trustee to institute such action, suit or proceeding in
its own name as Trustee hereunder and shall have offered to the Trustee such
reasonable indemnity as it may require against the costs, expenses and
liabilities to be incurred therein or thereby, and the Trustee for sixty (60)
days after its receipt of such notice, request and offer of indemnity, shall
have neglected or refused to institute any such action, suit or proceeding and
no direction inconsistent with such written request shall have been given to the
Trustee pursuant to Section 7.7; it being understood and intended, and being
expressly covenanted by the taker and holder of every Note with every other
taker and holder and the Trustee, that no one or more holders of Notes 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 holder of Notes, or to obtain or seek to obtain priority over or
preference to any other such holder, or to enforce any right under this
Indenture, except in the manner herein provided and for the equal, ratable and
common benefit of all holders of Notes (except as otherwise provided herein).
For the protection and enforcement of this Section 7.4, each and every
Noteholder and the Trustee shall be entitled to such relief as can be given
either at law or in equity.

     Notwithstanding any other provision of this Indenture and any provision of
any Note, the right of any holder of any Note to receive payment of the
principal of and premium, if any (including upon redemption pursuant to Article
III), and accrued interest on (including Liquidated Damages Amount, if any) such
Note, on or after the respective due dates expressed in such Note or in the
event of redemption, or to institute suit for the enforcement of any such
payment on or after such respective dates against the Company shall not be
impaired or affected without the consent of such holder.

     Anything in this Indenture or the Notes to the contrary notwithstanding,
the holder of any Note, without the consent of either the Trustee or the holder
of any other Note, in its own behalf and for its own benefit, may enforce, and
may institute and maintain any proceeding suitable to enforce, its rights of
conversion as provided herein.

     SECTION 7.5    PROCEEDINGS BY TRUSTEE.  In case of an Event of Default the
Trustee may in its discretion proceed to protect and enforce the rights vested
in it by this Indenture by such appropriate judicial proceedings as the Trustee
shall deem most effectual to protect and enforce any of such rights, either by
suit in equity or by action at law or by proceeding in bankruptcy or otherwise,
whether for the specific enforcement of any covenant or agreement contained in
this Indenture or in aid of the exercise of any power granted in this Indenture,
or to enforce any other legal or equitable right vested in the Trustee by this
Indenture or by law.

     SECTION 7.6    REMEDIES CUMULATIVE AND CONTINUING.  Except as provided in
Section 2.6, all powers and remedies given by this Article VII to the Trustee or
to the Noteholders shall, to the extent permitted by law, be deemed cumulative
and not exclusive of any thereof or of any other powers and remedies available
to the Trustee or the holders of the Notes, by judicial proceedings or
otherwise, to enforce the performance or observance of the covenants and
agreements contained in this Indenture, and no delay or omission of the Trustee
or of any holder of any of the Notes to exercise any right or power accruing
upon any default or Event of Default occurring and continuing as aforesaid shall
impair any such right or power, or shall be construed to be a waiver of any such
default or any acquiescence therein;

                                     -40-
<PAGE>
 
and, subject to the provisions of Section 7.4, every power and remedy given by
this Article VII or by law to the Trustee or to the Noteholders may be exercised
from time to time, and as often as shall be deemed expedient, by the Trustee or
by the Noteholders.

     SECTION 7.7    DIRECTION OF PROCEEDINGS AND WAIVER OF DEFAULTS BY MAJORITY
OF NOTEHOLDERS.  The holders of a majority in aggregate principal amount of the
Notes at the time outstanding determined in accordance with Section 9.4 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 the Trustee; provided, however, that (a) such direction shall
not be in conflict with any rule of law or with this Indenture, (b) the Trustee
may take any other action deemed proper by the Trustee which is not inconsistent
with such direction and (c) the Trustee may decline to take any action that
would benefit some Noteholder to the detriment of other Noteholders.  The
holders of a majority in aggregate principal amount of the Notes at the time
outstanding determined in accordance with Section 9.4 may on behalf of the
holders of all of the Notes waive any past default or Event of Default hereunder
and its consequences except (i) a default in the payment of interest (including
Liquidated Damages Amount, if any) or premium, if any, on, or the principal of,
the Notes, (ii) a failure by the Company to convert any Notes into Common Stock,
(iii) a default in the payment of redemption price pursuant to Article III or
(iv) a default in respect of a covenant or provisions hereof which under Article
XI cannot be modified or amended without the consent of the holders of each or
all Notes then outstanding or affected thereby.  Upon any such waiver, the
Company, the Trustee and the holders of the Notes shall be restored to their
former positions and rights hereunder; but no such waiver shall extend to any
subsequent or other default or Event of Default or impair any right consequent
thereon.  Whenever any default or Event of Default hereunder shall have been
waived as permitted by this Section 7.7, said default or Event of Default shall
for all purposes of the Notes and this Indenture be deemed to have been cured
and to be not continuing; but no such waiver shall extend to any subsequent or
other default or Event of Default or impair any right consequent thereon.

     SECTION 7.8    NOTICE OF DEFAULTS.  The Trustee shall, within ninety (90)
days after a Responsible Officer of the Trustee has knowledge of the occurrence
of a default, mail to all Noteholders, as the names and addresses of such
holders appear upon the Note register, notice of all defaults known to a
Responsible Officer, unless such defaults shall have been cured or waived before
the giving of such notice; and provided that, except in the case of default in
the payment of the principal of, or premium, if any, or interest (including
Liquidated Damages Amount, if any) on any of the Notes, the Trustee shall be
protected in withholding such notice if and so long as a trust committee of
directors and/or Responsible Officers of the Trustee in good faith determines
that the withholding of such notice is in the interests of the Noteholders.

     SECTION 7.9    UNDERTAKING TO PAY COSTS.  All parties to this Indenture
agree, and each holder of any Note by his acceptance thereof shall be deemed to
have agreed, that any court may, in its discretion, require, in any suit for the
enforcement of any right or remedy under this Indenture, or in any suit against
the Trustee for any action taken or omitted by it as Trustee, the filing by any
party litigant in such suit of an undertaking to pay the costs of such suit and
that such court may in its discretion assess reasonable costs, including
reasonable attorneys' fees, against any party litigant in such suit, having due
regard to the merits and good faith of the claims or defenses made by such party
litigant; provided that

                                     -41-
<PAGE>
 
the provisions of this Section 7.9 (to the extent permitted by law) shall not
apply to any suit instituted by the Trustee, to any suit instituted by any
Noteholder, or group of Noteholders, holding in the aggregate more than ten
percent in principal amount of the Notes at the time outstanding determined in
accordance with Section 9.4, or to any suit instituted by any Noteholder for the
enforcement of the payment of the principal of or premium, if any, or interest
on any Note on or after the due date expressed in such Note or to any suit for
the enforcement of the right to convert any Note in accordance with the
provisions of Article XV.


                                 ARTICLE VIII

                             CONCERNING THE TRUSTEE

     SECTION 8.1    DUTIES AND RESPONSIBILITIES OF TRUSTEE.  The Trustee, prior
to the occurrence of an Event of Default and after the curing of all Events of
Default which may have occurred, undertakes to perform such duties and only such
duties as are specifically set forth in this Indenture.  In case an Event of
Default has occurred (which has not been cured or waived) the Trustee shall
exercise such of the rights and powers vested in it by this Indenture, and use
the same degree of care and skill in their exercise, as a prudent man would
exercise or use under the circumstances in the conduct of his own affairs.

     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

          (a) prior to the occurrence of an Event of Default and after the
curing or waiving of all Events of Default which may have occurred:

                (1) the duties and obligations of the Trustee shall be
determined solely by the express provisions of this Indenture and the Trust
Indenture Act, and the Trustee shall not be liable except for the performance of
such duties and obligations as are specifically set forth in this Indenture and
no implied covenants or obligations shall be read into this Indenture and the
Trust Indenture Act against the Trustee; and

                (2) in the absence of bad faith and willful misconduct on the
part of the Trustee, the Trustee may conclusively rely, as to the truth of the
statements and the correctness of the opinions expressed therein, upon any
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 provisions 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) the Trustee shall not be liable for any error of judgment made in
good faith by a Responsible Officer or Officers of the Trustee, unless the
Trustee was negligent in ascertaining the pertinent facts;

                                     -42-
<PAGE>
 
          (c) 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 written
direction of the holders of not less than a majority in principal amount of the
Notes at the time outstanding determined as provided in Section 9.4 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;

          (d) whether or not therein 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;

          (e) the Trustee shall not be liable in respect of any payment (as to
the correctness of amount, entitlement to receive or any other matters relating
to payment) or notice effected by the Company or any paying agent or any records
maintained by any co-registrar with respect to the Notes; and

          (f) if any party fails to deliver a notice relating to an event the
fact of which, pursuant to this Indenture, requires notice to be sent to the
Trustee, the Trustee may conclusively rely on its failure to receive such notice
as reason to act as if no such event occurred.

     None of the provisions contained in this Indenture shall require the
Trustee to expend or risk its own funds or otherwise incur personal financial
liability in the performance of any of its duties or in the exercise of any of
its rights or powers, if there is reasonable ground for believing that the
repayment of such funds or adequate indemnity against such risk or liability is
not reasonably assured to it.

     SECTION 8.2    RELIANCE ON DOCUMENTS, OPINIONS, ETC.  Except as otherwise
provided in Section 8.1:

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

          (b) any request, direction, order or demand of the Company mentioned
herein shall be sufficiently evidenced by an Officers' Certificate (unless other
evidence in respect thereof be herein specifically prescribed); and any
resolution of the Board of Directors may be evidenced to the Trustee by a copy
thereof certified by the Secretary or an Assistant Secretary of the Company;

          (c) the Trustee may consult with counsel and any advice or Opinion of
Counsel shall be full and complete authorization and protection in respect of
any action taken or omitted by it hereunder in good faith and in accordance with
such advice or Opinion of Counsel;

          (d) the Trustee shall be under no obligation to exercise any of the
rights or powers vested in it by this Indenture at the request, order or
direction of any of the Noteholders pursuant to the

                                     -43-
<PAGE>
 
provisions of this Indenture, unless such Noteholders shall have offered to the
Trustee reasonable security or indemnity against the costs, expenses and
liabilities which may be incurred therein or thereby;

          (e) 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 or
other paper or 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;

          (f) the Trustee may execute any of the trusts or powers hereunder or
perform any duties hereunder either directly or by or through agents or
attorneys and the Trustee shall not be responsible for any misconduct or
negligence on the part of any agent or attorney appointed by it with due care
hereunder; and

          (g) the Trustee shall not be charged with knowledge of any default,
Event of Default or Fundamental Change unless either (1) a Responsible Officer
shall have actual knowledge of such default, Event of Default or Fundamental
Change or (2) written notice of such default, Event of Default or Fundamental
Change shall have been given to the Trustee by the Company or any other obligor
on the Notes or by any holder of the Notes.

     SECTION 8.3    NO RESPONSIBILITY FOR RECITALS, ETC.  The recitals contained
herein and in the Notes (except in the Trustee's certificate of authentication)
shall be taken as the statements of the Company, and the Trustee assumes no
responsibility for the correctness of the same.  The Trustee makes no
representations as to the validity or sufficiency of this Indenture or of the
Notes.  The Trustee shall not be accountable for the use or application by the
Company of any Notes or the proceeds of any Notes authenticated and delivered by
the Trustee in conformity with the provisions of this Indenture.

     SECTION 8.4    TRUSTEE, PAYING AGENTS, CONVERSION AGENTS OR REGISTRAR MAY
OWN NOTES.  The Trustee, any paying agent, any conversion agent or Note
registrar, in its individual or any other capacity, may become the owner or
pledgee of Notes with the same rights it would have if it were not Trustee,
paying agent, conversion agent or Note registrar.

     SECTION 8.5    MONIES TO BE HELD IN TRUST.  Subject to the provisions of
Section 13.4 and Section 4.2, all monies received by the Trustee shall, until
used or applied as herein provided, be held in trust for the purposes for which
they were received.  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 may be agreed in writing from time to time by the Company and the
Trustee.

     SECTION 8.6    COMPENSATION AND EXPENSES OF TRUSTEE.  The Company covenants
and agrees to pay to the Trustee from time to time, and the Trustee shall be
entitled to, reasonable compensation for all services rendered by it hereunder
in any capacity (which shall not be limited by any provision of law in regard to
the compensation of a trustee of an express trust) as mutually agreed to in
writing

                                     -44-
<PAGE>
 
between the Company and the Trustee, and the Company will pay or reimburse the
Trustee upon its request for all reasonable expenses, disbursements and advances
reasonably incurred or made by the Trustee in accordance with any of the
provisions of this Indenture (including the reasonable compensation and the
expenses and disbursements of its counsel and of all Persons not regularly in
its employ) except any such expense, disbursement or advance as may arise from
its negligence, willful misconduct or bad faith.  The Company also covenants to
indemnify the Trustee (or any officer, director or employee of the Trustee) in
any capacity under this Indenture and its agents and any authenticating agent
for, and to hold them harmless against, any loss, liability or expense incurred
without negligence, willful misconduct or bad faith on the part of the Trustee
or such officers, directors, employees and agent or authenticating agent, as the
case may be, and arising out of or in connection with the acceptance or
administration of this trust or in any other capacity hereunder, including the
costs and expenses of defending themselves against any claim of liability in the
premises.  The obligations of the Company under this Section 8.6 to compensate
or indemnify the Trustee and to pay or reimburse the Trustee for expenses,
disbursements and advances shall be secured by a lien prior to that of the Notes
upon all property and funds held or collected by the Trustee as such, except
funds held in trust for the benefit of the holders of particular Notes.  The
obligation of the Company under this Section shall survive the resignation or
removal of the Trustee and the satisfaction and discharge of this Indenture.

     When the Trustee and its agents and any authenticating agent incur expenses
or render services after an Event of Default specified in Section 7.1(d) or (e)
with respect to the Company occurs, the expenses and the compensation for the
services are intended to constitute expenses of administration under any
bankruptcy, insolvency or similar laws.

     SECTION 8.7    OFFICERS' CERTIFICATE AS EVIDENCE.  Except as otherwise
provided in Section 8.1, whenever in the administration of the provisions of
this Indenture the Trustee shall deem it necessary or desirable that a matter be
proved or established prior to taking or omitting any action hereunder, such
matter (unless other evidence in respect thereof be herein specifically
prescribed) may, in the absence of negligence, willful misconduct, or bad faith
on the part of the Trustee, be deemed to be conclusively proved and established
by an Officers' Certificate delivered to the Trustee.

     SECTION 8.8    CONFLICTING INTERESTS OF TRUSTEE.  If the Trustee has or
shall acquire a conflicting interest within the meaning of the Trust Indenture
Act, the Trustee shall either eliminate such interest or resign, to the extent
and in the manner provided by, and subject to the provisions of, the Trust
Indenture Act and this Indenture.

     SECTION 8.9    ELIGIBILITY OF TRUSTEE.  There shall at all times be a
Trustee hereunder which shall be a Person that is eligible pursuant to the Trust
Indenture Act to act as such and has a combined capital and surplus of at least
$50,000,000 (or if such Person is a member of a bank holding company system, its
bank holding company shall have a combined capital and surplus of at least
$50,000,000).  If such Person publishes reports of condition at least annually,
pursuant to law or to the requirements of any supervising or examining
authority, then for the purposes of this Section, the combined capital and
surplus of such Person 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

                                     -45-
<PAGE>
 
with the provisions of this Section, it shall resign immediately in the manner
and with the effect hereinafter specified in this Article.

     SECTION 8.10   RESIGNATION OR REMOVAL OF TRUSTEE.

          (a) The Trustee may at any time resign by giving written notice of
such resignation to the Company and to the holders of Notes. Upon receiving such
notice of resignation, the Company shall promptly appoint a successor trustee by
written instrument, in duplicate, executed by order of the Board of Directors,
one copy of which instrument shall be delivered to the resigning Trustee and one
copy to the successor trustee. If no successor trustee shall have been so
appointed and have accepted appointment sixty (60) days after the mailing of
such notice of resignation to the Noteholders, the resigning Trustee may
petition any court of competent jurisdiction for the appointment of a successor
trustee, or, if any Noteholder who has been a bona fide holder of a Note or
Notes for at least six (6) months may, subject to the provisions of Section 7.9,
on behalf of himself and all others similarly situated, petition any such court
for the appointment of a successor trustee. Such court may thereupon, after such
notice, if any, as it may deem proper and prescribe, appoint a successor
trustee.

          (b) In case at any time any of the following shall occur:

                (1) the Trustee shall fail to comply with Section 8.8 after
written request therefor by the Company or by any Noteholder who has been a bona
fide holder of a Note or Notes for at least six (6) months; or

                (2) the Trustee shall cease to be eligible in accordance with
the provisions of Section 8.9 and shall fail to resign after written request
therefor by the Company or by any such Noteholder; or

                (3) the Trustee shall become incapable of acting, or shall be
adjudged a bankrupt or insolvent, or a receiver of the Trustee or of its
property shall be appointed, or any public officer shall take charge or control
of the Trustee or of its property or affairs for the purpose of rehabilitation,
conservation or liquidation;

then, in any such case, the Company may remove the Trustee and appoint a
successor trustee by written instrument, in duplicate, executed by order of the
Board of Directors, one copy of which instrument shall be delivered to the
Trustee so removed and one copy to the successor trustee, or, subject to the
provisions of Section 7.9, any Noteholder who has been a bona fide holder of a
Note or Notes for at least six (6) months may, on behalf of himself and all
others similarly situated, petition any court of competent jurisdiction for the
removal of the Trustee and the appointment of a successor trustee; provided that
if no successor Trustee shall have been appointed and have accepted appointment
sixty (60) days after either the Company or the Noteholders has removed the
Trustee, the Trustee so removed may petition any court of competent jurisdiction
for an appointment of a successor trustee.  Such court may thereupon, after such
notice, if any, as it may deem proper and prescribe, remove the Trustee and
appoint a successor trustee.

                                     -46-
<PAGE>
 
          (c) The holders of a majority in aggregate principal amount of the
Notes at the time outstanding may at any time remove the Trustee and nominate a
successor trustee which shall be deemed appointed as successor trustee unless
within ten (10) days after notice to the Company of such nomination the Company
objects thereto, in which case the Trustee so removed or any Noteholder, or if
such Trustee so removed or any Noteholder fails to act, the Company, upon the
terms and conditions and otherwise as in Section 8.10(a) provided, may petition
any court of competent jurisdiction for an appointment of a successor trustee.

          (d) Any resignation or removal of the Trustee and appointment of a
successor trustee pursuant to any of the provisions of this Section 8.10 shall
become effective upon acceptance of appointment by the successor trustee as
provided in Section 8.11.

     SECTION 8.11   ACCEPTANCE BY SUCCESSOR TRUSTEE.  Any successor trustee
appointed as provided in Section 8.10 shall execute, acknowledge and deliver to
the Company and to its predecessor trustee an instrument accepting such
appointment hereunder, and thereupon the resignation or removal of the
predecessor trustee shall become effective and such successor trustee, without
any further act, deed or conveyance, shall become vested with all the rights,
powers, duties and obligations of its predecessor hereunder, with like effect as
if originally named as trustee herein; but, nevertheless, on the written request
of the Company or of the successor trustee, the trustee ceasing to act shall,
upon payment of any amounts then due it pursuant to the provisions of Section
8.6, execute and deliver an instrument transferring to such successor trustee
all the rights and powers of the trustee so ceasing to act.  Upon request of any
such successor trustee, the Company shall execute any and all instruments in
writing for more fully and certainly vesting in and confirming to such successor
trustee all such rights and powers.  Any trustee ceasing to act shall,
nevertheless, retain a lien upon all property and funds held or collected by
such trustee as such, except for funds held in trust for the benefit of holders
of particular Notes, to secure any amounts then due it pursuant to the
provisions of Section 8.6.

     No successor trustee shall accept appointment as provided in this Section
8.11 unless at the time of such acceptance such successor trustee shall be
qualified under the provisions of Section 8.8 and be eligible under the
provisions of Section 8.9.

     Upon acceptance of appointment by a successor trustee as provided in this
Section 8.11, the Company (or the former trustee, at the written direction of
the Company) shall mail or cause to be mailed notice of the succession of such
trustee hereunder to the holders of Notes at their addresses as they shall
appear on the Note register.  If the Company fails to mail such notice within
ten (10) days after acceptance of appointment by the successor trustee, the
successor trustee shall cause such notice to be mailed at the expense of the
Company.

     SECTION 8.12   SUCCESSION BY MERGER, ETC.  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 of the corporate trust business of the Trustee (including any trust created
by this Indenture), shall be the successor to the Trustee hereunder without the
execution or filing of any paper or any further act on the part of any of the
parties hereto, provided that in the case of any corporation

                                     -47-
<PAGE>
 
succeeding to all or substantially all of the corporate trust business of the
Trustee such corporation shall be qualified under the provisions of Section 8.8
and eligible under the provisions of Section 8.9.

     In case at the time such successor to the Trustee shall succeed to the
trusts created by this Indenture, any of the Notes shall have been authenticated
but not delivered, any such successor to the Trustee may adopt the certificate
of authentication of any predecessor trustee or authenticating agent appointed
by such predecessor trustee, and deliver such Notes so authenticated; and in
case at that time any of the Notes shall not have been authenticated, any
successor to the Trustee or an authenticating agent appointed by such successor
trustee may authenticate such Notes either in the name of any predecessor
trustee hereunder or in the name of the successor trustee; and in all such cases
such certificates shall have the full force which it is anywhere in the Notes or
in this Indenture provided that the certificate of the Trustee shall have;
provided, however, that the right to adopt the certificate of authentication of
any predecessor Trustee or authenticate Notes in the name of any predecessor
Trustee shall apply only to its successor or successors by merger, conversion or
consolidation.

     SECTION 8.13   PREFERENTIAL COLLECTION OF CLAIMS.  If and when the Trustee
shall be or become a creditor of the Company (or any other obligor upon the
Notes), the Trustee shall be subject to the provisions of the Trust Indenture
Act regarding the collection of the claims against the Company (or any such
other obligor).

     SECTION 8.14   TRUSTEE'S APPLICATION FOR INSTRUCTIONS FROM THE COMPANY.
Any application by the Trustee for written instructions from the Company (other
than with regard to any action proposed to be taken or omitted to be taken by
the Trustee that affects the rights of the holders of the Notes or holders of
Senior Indebtedness under this Indenture, including, without limitation, under
Article IV hereof) 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 three (3) 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 IX

                          CONCERNING THE NOTEHOLDERS

     SECTION 9.1    ACTION BY NOTEHOLDERS.  Whenever in this Indenture it is
provided that the holders of a specified percentage in aggregate principal
amount of the Notes may take any action (including the making of any demand or
request, the giving of any notice, consent or waiver or the taking of any other
action), the fact that at the time of taking any such action, the holders of
such specified percentage have joined therein may be evidenced (a) by any
instrument or any number of instruments

                                     -48-
<PAGE>
 
of similar tenor executed by Noteholders in person or by agent or proxy
appointed in writing, or (b) by the record of the holders of Notes voting in
favor thereof at any meeting of Noteholders duly called and held in accordance
with the provisions of Article X, or (c) by a combination of such instrument or
instruments and any such record of such a meeting of Noteholders.  Whenever the
Company or the Trustee solicits the taking of any action by the holders of the
Notes, the Company or the Trustee may fix in advance of such solicitation, a
date as the record date for determining holders entitled to take such action.
The record date shall be not more than fifteen (15) days prior to the date of
commencement of solicitation of such action.

     SECTION 9.2    PROOF OF EXECUTION BY NOTEHOLDERS.  Subject to the
provisions of Sections 8.1, 8.2 and 10.5, proof of the execution of any
instrument by a Noteholder or its agent or proxy shall be sufficient if made in
accordance with such reasonable rules and regulations as may be prescribed by
the Trustee or in such manner as shall be satisfactory to the Trustee.  The
holding of Notes shall be proved by the registry of such Notes or by a
certificate of the Note registrar.

     The record of any Noteholders' meeting shall be proved in the manner
provided in Section 10.6.

     SECTION 9.3    WHO ARE DEEMED ABSOLUTE OWNERS.  The Company, the Trustee,
any paying agent, any conversion agent and any Note registrar may deem the
Person in whose name such Note shall be registered upon the Note register to be,
and may treat it as, the absolute owner of such Note (whether or not such Note
shall be overdue and notwithstanding any notation of ownership or other writing
thereon) for the purpose of receiving payment of or on account of the principal
of, premium, if any, and interest on such Note, for conversion of such Note and
for all other purposes; and neither the Company nor the Trustee nor any paying
agent nor any conversion agent nor any Note registrar shall be affected by any
notice to the contrary.  All such payments so made to any holder for the time
being, or upon his order, shall be valid, and, to the extent of the sum or sums
so paid, effectual to satisfy and discharge the liability for monies payable
upon any such Note.

     SECTION 9.4    COMPANY-OWNED NOTES DISREGARDED.  In determining whether the
holders of the requisite aggregate principal amount of Notes have concurred in
any direction, consent, waiver or other action under this Indenture, Notes which
are owned by the Company or any other obligor on the Notes or any Affiliate of
the Company or any other obligor on the Notes shall be disregarded and deemed
not to be outstanding for the purpose of any such determination; provided that
for the purposes of determining whether the Trustee shall be protected in
relying on any such direction, consent, waiver or other action only Notes which
a Responsible Officer knows are so owned shall be so disregarded.  Notes so
owned which have been pledged in good faith may be regarded as outstanding for
the purposes of this Section 9.4 if the pledgee shall establish to the
satisfaction of the Trustee the pledgee's right to vote such Notes and that the
pledgee is not the Company, any other obligor on the Notes or any Affiliate of
the Company or any such other obligor.  In the case of a dispute as to such
right, any decision by the Trustee taken upon the advice of counsel shall be
full protection to the Trustee.  Upon request of the Trustee, the Company shall
furnish to the Trustee promptly an Officers' Certificate listing and identifying
all Notes, if any, known by the Company to be owned or held by or for the
account of any of the above described Persons; and, subject to Section 8.1, the
Trustee shall be entitled to accept such

                                     -49-
<PAGE>
 
Officers' Certificate as conclusive evidence of the facts therein set forth and
of the fact that all Notes not listed therein are outstanding for the purpose of
any such determination.

     SECTION 9.5    REVOCATION OF CONSENTS; FUTURE HOLDERS BOUND.  At any time
prior to (but not after) the evidencing to the Trustee, as provided in Section
9.1, of the taking of any action by the holders of the percentage in aggregate
principal amount of the Notes specified in this Indenture in connection with
such action, any holder of a Note which is shown by the evidence to be included
in the Notes the holders of which have consented to such action may, by filing
written notice with the Trustee at its Corporate Trust Office and upon proof of
holding as provided in Section 9.2, revoke such action so far as concerns such
Note.  Except as aforesaid, any such action taken by the holder of any Note
shall be conclusive and binding upon such holder and upon all future holders and
owners of such Note and of any Notes issued in exchange or substitution
therefor, irrespective of whether any notation in regard thereto is made upon
such Note or any Note issued in exchange or substitution therefor.


                                   ARTICLE X

                             NOTEHOLDERS' MEETINGS

     SECTION 10.1   PURPOSE OF MEETINGS.  A meeting of Noteholders may be called
at any time and from time to time pursuant to the provisions of this Article X
for any of the following purposes:

                (1) to give any notice to the Company or to the Trustee or to
give any directions to the Trustee permitted under this Indenture, or to consent
to the waiving of any default or Event of Default hereunder and its
consequences, or to take any other action authorized to be taken by Noteholders
pursuant to any of the provisions of Article VII;

                (2) to remove the Trustee and nominate a successor trustee
pursuant to the provisions of Article VIII;

                (3) to consent to the execution of an indenture or indentures
supplemental hereto pursuant to the provisions of Section 11.2; or

                (4) to take any other action authorized to be taken by or on
behalf of the holders of any specified aggregate principal amount of the Notes
under any other provision of this Indenture or under applicable law.

     SECTION 10.2   CALL OF MEETINGS BY TRUSTEE.  The Trustee may at any time
call a meeting of Noteholders to take any action specified in Section 10.1, to
be held at such time and at such place as the Trustee shall determine.  Notice
of every meeting of the Noteholders, setting forth the time and the place of
such meeting and in general terms the action proposed to be taken at such
meeting and the establishment of any record date pursuant to Section 9.1, shall
be mailed to holders of Notes at their addresses as they shall appear on the
Note register.  Such notice shall also be mailed to the Company.

                                     -50-
<PAGE>
 
Such notices shall be mailed not less than twenty (20) nor more than ninety (90)
days prior to the date fixed for the meeting.

     Any meeting of Noteholders shall be valid without notice if the holders of
all Notes then outstanding are present in person or by proxy or if notice is
waived before or after the meeting by the holders of all Notes outstanding, and
if the Company and the Trustee are either present by duly authorized
representatives or have, before or after the meeting, waived notice.

     SECTION 10.3   CALL OF MEETINGS BY COMPANY OR NOTEHOLDERS.  In case at any
time the Company, pursuant to a resolution of its Board of Directors, or the
holders of at least ten percent (10%) in aggregate principal amount of the Notes
then outstanding, shall have requested the Trustee to call a meeting of
Noteholders, by written request setting forth in reasonable detail the action
proposed to be taken at the meeting, and the Trustee shall not have mailed the
notice of such meeting within twenty (20) days after receipt of such request,
then the Company or such Noteholders may determine the time and the place for
such meeting and may call such meeting to take any action authorized in Section
10.1, by mailing notice thereof as provided in Section 10.2.

     SECTION 10.4   QUALIFICATIONS FOR VOTING.  To be entitled to vote at any
meeting of Noteholders a person shall (a) be a holder of one or more Notes on
the record date pertaining to such meeting or (b) be a person appointed by an
instrument in writing as proxy by a holder of one or more Notes.  The only
persons who shall be entitled to be present or to speak at any meeting of
Noteholders shall be the persons entitled to vote at such meeting and their
counsel and any representatives of the Trustee and its counsel and any
representatives of the Company and its counsel.

     SECTION 10.5   REGULATIONS.  Notwithstanding any other provisions of this
Indenture, the Trustee may make such reasonable regulations as it may deem
advisable for any meeting of Noteholders, in regard to proof of the holding of
Notes and of the appointment of proxies, and in regard to the appointment and
duties of inspectors of votes, the submission and examination of proxies,
certificates and other evidence of the right to vote, and such other matters
concerning the conduct of the meeting as it shall think fit.

     The Trustee shall, by an instrument in writing, appoint a temporary
chairman of the meeting, unless the meeting shall have been called by the
Company or by Noteholders as provided in Section 10.3, in which case the Company
or the Noteholders calling the meeting, as the case may be, shall in like manner
appoint a temporary chairman.  A permanent chairman and a permanent secretary of
the meeting shall be elected by vote of the holders of a majority in principal
amount of the Notes represented at the meeting and entitled to vote at the
meeting.

     Subject to the provisions of Section 9.4, at any meeting each Noteholder or
proxyholder shall be entitled to one vote for each $1,000 principal amount of
Notes held or represented by him; provided, however, that no vote shall be cast
or counted at any meeting in respect of any Note challenged as not outstanding
and ruled by the chairman of the meeting to be not outstanding.  The chairman of
the meeting shall have no right to vote other than by virtue of Notes held by
him or instruments in writing as aforesaid duly designating him as the proxy to
vote on behalf of other Noteholders.  Any meeting of

                                     -51-
<PAGE>
 
Noteholders duly called pursuant to the provisions of Section 10.2 or 10.3 may
be adjourned from time to time by the holders of a majority of the aggregate
principal amount of Notes represented at the meeting, whether or not
constituting a quorum, and the meeting may be held as so adjourned without
further notice.

     SECTION 10.6   VOTING.  The vote upon any resolution submitted to any
meeting of Noteholders shall be by written ballot on which shall be subscribed
the signatures of the holders of Notes or of their representatives by proxy and
the principal amount of the Notes held or represented by them.  The permanent
chairman of the meeting shall appoint two inspectors of votes who shall count
all votes cast at the meeting for or against any resolution and who shall make
and file with the secretary of the meeting their verified written reports in
duplicate of all votes cast at the meeting.  A record in duplicate of the
proceedings of each meeting of Noteholders shall be prepared by the secretary of
the meeting and there shall be attached to said record the original reports of
the inspectors of votes on any vote by ballot taken thereat and affidavits by
one or more persons having knowledge of the facts setting forth a copy of the
notice of the meeting and showing that said notice was mailed as provided in
Section 10.2.  The record shall show the principal amount of the Notes voting in
favor of or against any resolution.  The record shall be signed and verified by
the affidavits of the permanent chairman and secretary of the meeting and one of
the duplicates shall be delivered to the Company and the other to the Trustee to
be preserved by the Trustee, the latter to have attached thereto the ballots
voted at the meeting.

     Any record so signed and verified shall be conclusive evidence of the
matters therein stated.

     SECTION 10.7   NO DELAY OF RIGHTS BY MEETING.  Nothing in this Article X
contained shall be deemed or construed to authorize or permit, by reason of any
call of a meeting of Noteholders or any rights expressly or impliedly conferred
hereunder to make such call, any hindrance or delay in the exercise of any right
or rights conferred upon or reserved to the Trustee or to the Noteholders under
any of the provisions of this Indenture or of the Notes.


                                  ARTICLE XI

                            SUPPLEMENTAL INDENTURES

     SECTION 11.1   SUPPLEMENTAL INDENTURES WITHOUT CONSENT OF NOTEHOLDERS.  The
Company, when authorized by the resolutions of the Board of Directors, and the
Trustee may from time to time and at any time enter into an indenture or
indentures supplemental hereto for one or more of the following purposes:

          (a) to make provision with respect to the conversion rights of the
holders of Notes pursuant to the requirements of Section 15.6 and the redemption
obligations of the Company pursuant to the requirements of Section 3.5(e);

          (b) subject to Article IV, to convey, transfer, assign, mortgage or
pledge to the Trustee as security for the Notes, any property or assets;

                                     -52-
<PAGE>
 
          (c) to evidence the succession of another Person to the Company, or
successive successions, and the assumption by the successor Person of the
covenants, agreements and obligations of the Company pursuant to Article XII;

          (d) to add to the covenants of the Company such further covenants,
restrictions or conditions as the Board of Directors and the Trustee shall
consider to be for the benefit of the holders of Notes, and to make the
occurrence, or the occurrence and continuance, of a default in any such
additional covenants, restrictions or conditions a default or an Event of
Default permitting the enforcement of all or any of the several remedies
provided in this Indenture as herein set forth; provided, however, that in
respect of any such additional covenant, restriction or condition such
supplemental indenture may provide for a particular period of grace after
default (which period may be shorter or longer than that allowed in the case of
other defaults) or may provide for an immediate enforcement upon such default or
may limit the remedies available to the Trustee upon such default;

          (e) to provide for the issuance under this Indenture of Notes in
coupon form (including Notes registrable as to principal only) and to provide
for exchangeability of such Notes with the Notes issued hereunder in fully
registered form and to make all appropriate changes for such purpose;

          (f) to cure any ambiguity or to correct or supplement any provision
contained herein or in any supplemental indenture which may be defective or
inconsistent with any other provision contained herein or in any supplemental
indenture, or to make such other provisions in regard to matters or questions
arising under this Indenture which shall not materially adversely affect the
interests of the holders of the Notes;

          (g) to evidence and provide for the acceptance of appointment
hereunder by a successor Trustee with respect to the Notes; or

          (h) to modify, eliminate or add to the provisions of this Indenture to
such extent as shall be necessary to effect the qualifications of this Indenture
under the Trust Indenture Act, or under any similar federal statute hereafter
enacted.

     Upon the written request of the Company, accompanied by a copy of the
resolutions of the Board of Directors certified by its Secretary or Assistant
Secretary authorizing the execution of any supplemental indenture, the Trustee
is hereby authorized to join with the Company in the execution of any such
supplemental indenture, to make any further appropriate agreements and
stipulations which may be therein contained and to accept the conveyance,
transfer and assignment of any property thereunder, but the Trustee shall not be
obligated to, but may in its discretion, enter into any supplemental indenture
which affects the Trustee's own rights, duties or immunities under this
Indenture or otherwise.

     Any supplemental indenture authorized by the provisions of this Section
11.1 may be executed by the Company and the Trustee without the consent of the
holders of any of the Notes at the time outstanding, notwithstanding any of the
provisions of Section 11.2.

                                     -53-
<PAGE>
 
     Notwithstanding any other provision of the Indenture or the Notes, the
Registration Rights Agreement and the obligation to pay Liquidated Damages
Amount thereunder may be amended, modified or waived in accordance with the
provisions of the Registration Rights Agreement.

     SECTION 11.2   SUPPLEMENTAL INDENTURES WITH CONSENT OF NOTEHOLDERS.  With
the consent (evidenced as provided in Article IX) of the holders of not less
than a majority in aggregate principal amount of the Notes at the time
outstanding, the Company, when authorized by the resolutions of the Board of
Directors, and the Trustee may from time to time and at any time enter into an
indenture or indentures supplemental hereto for the purpose of adding any
provisions to or changing in any manner or eliminating any of the provisions of
this Indenture or any supplemental indenture or of modifying in any manner the
rights of the holders of the Notes; provided, however, that no such supplemental
indenture shall (i) extend the fixed maturity of any Note, or reduce the rate or
extend the time of payment of interest thereon, or reduce the principal amount
thereof or premium, if any, thereon, or reduce any amount payable on redemption
thereof, or impair the right of any Noteholder to institute suit for the payment
thereof, or make the principal thereof or interest or premium, if any, thereon
payable in any coin or currency other than that provided in the Notes, or modify
the provisions of this Indenture with respect to the subordination of the Notes
in a manner adverse to the Noteholders in any material respect, or change the
obligation of the Company to redeem any Note upon the happening of a Fundamental
Change in a manner adverse to the holder of Notes, or impair the right to
convert the Notes into Common Stock subject to the terms set forth herein,
including Section 15.6, in each case, without the consent of the holder of each
Note so affected, or (ii) reduce the aforesaid percentage of Notes, the holders
of which are required to consent to any such supplemental indenture, without the
consent of the holders of all Notes then outstanding.

     Upon the written request of the Company, accompanied by a copy of the
resolutions of the Board of Directors certified by its Secretary or Assistant
Secretary authorizing the execution of any such supplemental indenture, and upon
the filing with the Trustee of evidence of the consent of Noteholders as
aforesaid, the Trustee shall join with the Company in the execution of such
supplemental indenture unless such supplemental indenture affects the Trustee's
own rights, duties or immunities under this Indenture or otherwise, in which
case the Trustee may in its discretion, but shall not be obligated to, enter
into such supplemental indenture.

     It shall not be necessary for the consent of the Noteholders under this
Section 11.2 to approve the particular form of any proposed supplemental
indenture, but it shall be sufficient if such consent shall approve the
substance thereof.

     SECTION 11.3   EFFECT OF SUPPLEMENTAL INDENTURE.  Any supplemental
indenture executed pursuant to the provisions of this Article XI shall comply
with the Trust Indenture Act, as then in effect; provided that this Section 11.3
shall not require such supplemental indenture or the Trustee to be qualified
under the Trust Indenture Act prior to the time such qualification is in fact
required under the terms of the Trust Indenture Act or the Indenture has been
qualified under the Trust Indenture Act, nor shall it constitute any admission
or acknowledgment by any party to such supplemental indenture that any such
qualification is required prior to the time such qualification is in fact
required under the terms of the Trust Indenture Act or the Indenture has been
qualified under the Trust Indenture Act.  Upon the

                                     -54-
<PAGE>
 
execution of any supplemental indenture pursuant to the provisions of this
Article XI, this Indenture shall be and be deemed to be modified and amended in
accordance therewith and the respective rights, limitation of rights,
obligations, duties and immunities under this Indenture of the Trustee, the
Company and the holders of Notes shall thereafter be determined, exercised and
enforced hereunder subject in all respects to such modifications and amendments
and all the terms and conditions of any such supplemental indenture shall be and
be deemed to be part of the terms and conditions of this Indenture for any and
all purposes.

     SECTION 11.4   NOTATION ON NOTES.  Notes authenticated and delivered after
the execution of any supplemental indenture pursuant to the provisions of this
Article XI may bear a notation in form approved by the Trustee as to any matter
provided for in such supplemental indenture.  If the Company or the Trustee
shall so determine, new Notes so modified as to conform, in the opinion of the
Trustee and the Board of Directors, to any modification of this Indenture
contained in any such supplemental indenture may, at the Company's expense, be
prepared and executed by the Company, authenticated by the Trustee (or an
authenticating agent duly appointed by the Trustee pursuant to Section 16.11)
and delivered in exchange for the Notes then outstanding, upon surrender of such
Notes then outstanding.

     SECTION 11.5   EVIDENCE OF COMPLIANCE OF SUPPLEMENTAL INDENTURE TO BE
FURNISHED TRUSTEE.  Prior to entering into any supplemental indenture, the
Trustee may request an Officers' Certificate and an Opinion of Counsel meeting
the requirements set forth in Section 16.5 as conclusive evidence that any
supplemental indenture executed pursuant hereto complies with the requirements
of this Article XI.


                                  ARTICLE XII

               CONSOLIDATION, MERGER, SALE, CONVEYANCE AND LEASE

     SECTION 12.1   COMPANY MAY CONSOLIDATE ETC. ON CERTAIN TERMS.  Subject to
the provisions of Section 12.2, nothing contained in this Indenture or in any of
the Notes shall prevent any consolidation or merger of the Company with or into
any other Person or Persons (whether or not affiliated with the Company), or
successive consolidations or mergers in which the Company or its successor or
successors shall be a party or parties, or shall prevent any sale, conveyance or
lease (or successive sales, conveyances or leases) of all or substantially all
of the property of the Company, to any other Person (whether or not affiliated
with the Company), authorized to acquire and operate the same and which shall be
organized under the laws of the United States of America, any state thereof or
the District of Columbia; provided that upon any such consolidation, merger,
sale, conveyance or lease, the due and punctual payment of the principal of and
premium, if any, and interest (including Liquidated Damages Amount, if any) on
all of the Notes, according to their tenor, and the due and punctual performance
and observance of all of the covenants and conditions of this Indenture to be
performed by the Company, shall be expressly assumed, by supplemental indenture
satisfactory in form to the Trustee, executed and delivered to the Trustee by
the Person (if other than the Company) formed by such consolidation, or into
which the Company shall have been merged, or by the Person which shall have
acquired or leased such property, and such supplemental indenture shall provide
for the applicable conversion rights set forth in Section 15.6.


                                     -55-
<PAGE>
 
     SECTION 12.2   SUCCESSOR CORPORATION TO BE SUBSTITUTED. In case of any such
consolidation, merger, sale, conveyance or lease and upon the assumption by the
successor Person, by supplemental indenture, executed and delivered to the
Trustee and satisfactory in form to the Trustee, of the due and punctual payment
of the principal of and premium, if any, and interest on all of the Notes and
the due and punctual performance of all of the covenants and conditions of this
Indenture to be performed by the Company, such successor Person shall succeed to
and be substituted for the Company, with the same effect as if it had been named
herein as the party of the first part. Such successor Person thereupon may cause
to be signed, and may issue either in its own name or in the name of Aviron any
or all of the Notes issuable hereunder which theretofore shall not have been
signed by the Company and delivered to the Trustee; and, upon the order of such
successor Person instead of the Company and subject to all the terms, conditions
and limitations in this Indenture prescribed, the Trustee shall authenticate and
shall deliver, or cause to be authenticated and delivered, any Notes which
previously shall have been signed and delivered by the officers of the Company
to the Trustee for authentication, and any Notes which such successor Person
thereafter shall cause to be signed and delivered to the Trustee for that
purpose. All the Notes so issued shall in all respects have the same legal rank
and benefit under this Indenture as the Notes theretofore or thereafter issued
in accordance with the terms of this Indenture as though all of such Notes had
been issued at the date of the execution hereof. In the event of any such
consolidation, merger, sale, conveyance or lease, the Person named as the
"Company" in the first paragraph of this Indenture or any successor which shall
thereafter have become such in the manner prescribed in this Article XII may be
dissolved, wound up and liquidated at any time thereafter and such Person shall
be released from its liabilities as obligor and maker of the Notes and from its
obligations under this Indenture.

     In case of any such consolidation, merger, sale, conveyance or lease, such
changes in phraseology and form (but not in substance) may be made in the Notes
thereafter to be issued as may be appropriate.

     SECTION 12.3   OPINION OF COUNSEL TO BE GIVEN TRUSTEE.  The Trustee shall
receive an Officers' Certificate and an Opinion of Counsel as conclusive
evidence that any such consolidation, merger, sale, conveyance or lease and any
such assumption complies with the provisions of this Article XII.


                                 ARTICLE XIII

                    SATISFACTION AND DISCHARGE OF INDENTURE

     SECTION 13.1   DISCHARGE OF INDENTURE.  When (a) the Company shall deliver
to the Trustee for cancellation all Notes theretofore authenticated (other than
any Notes which have been destroyed, lost or stolen and in lieu of or in
substitution for which other Notes shall have been authenticated and delivered)
and not theretofore canceled, or (b) all the Notes not theretofore canceled or
delivered to the Trustee for cancellation shall have become due and payable, or
are by their terms to become due and payable within one year or are to be called
for redemption within one year under arrangements satisfactory to the Trustee
for the giving of notice of redemption, and the Company shall deposit with the
Trustee, in trust, funds sufficient to pay at maturity or upon redemption of all
of the Notes (other than any Notes which shall have been mutilated, destroyed,
lost or stolen and in lieu of or in substitution for

                                     -56-
<PAGE>
 
which other Notes shall have been authenticated and delivered) not theretofore
canceled or delivered to the Trustee for cancellation, including principal and
premium, if any, and interest due or to become due to such date of maturity or
redemption date, as the case may be, accompanied by a verification report, as to
the sufficiency of the deposited amount, from an independent certified
accountant or other financial professional satisfactory to the Trustee, and if
the Company shall also pay or cause to be paid all other sums payable hereunder
by the Company, then this Indenture shall cease to be of further effect (except
as to (i) remaining rights of registration of transfer, substitution and
exchange and conversion of Notes, (ii) rights hereunder of Noteholders to
receive payments of principal of and premium, if any, and interest on, the Notes
and the other rights, duties and obligations of Noteholders, as beneficiaries
hereof with respect to the amounts, if any, so deposited with the Trustee and
(iii) the rights, obligations and immunities of the Trustee hereunder), and the
Trustee, on written demand of the Company accompanied by an Officers'
Certificate and an Opinion of Counsel as required by Section 16.5 and at the
cost and expense of the Company, shall execute proper instruments acknowledging
satisfaction of and discharging this Indenture; the Company, however, hereby
agreeing to reimburse the Trustee for any costs or expenses thereafter
reasonably and properly incurred by the Trustee and to compensate the Trustee
for any services thereafter reasonably and properly rendered by the Trustee in
connection with this Indenture or the Notes.

     SECTION 13.2   DEPOSITED MONIES TO BE HELD IN TRUST BY TRUSTEE.  Subject to
Section 13.4, all monies deposited with the Trustee pursuant to Section 13.1,
provided such deposit was not in violation of Article IV, shall be held in trust
for the sole benefit of the Noteholders and not to be subject to the
subordination provisions of Article IV, and such monies shall be applied by the
Trustee to the payment, either directly or through any paying agent (including
the Company if acting as its own paying agent), to the holders of the particular
Notes for the payment or redemption of which such monies have been deposited
with the Trustee, of all sums due and to become due thereon for principal and
interest and premium, if any.

     SECTION 13.3   PAYING AGENT TO REPAY MONIES HELD.  Upon the satisfaction
and discharge of this Indenture, all monies then held by any paying agent of the
Notes (other than the Trustee) shall, upon written request of the Company, be
repaid to it or paid to the Trustee, and thereupon such paying agent shall be
released from all further liability with respect to such monies.

     SECTION 13.4   RETURN OF UNCLAIMED MONIES.  Subject to the requirements of
applicable law, any monies deposited with or paid to the Trustee for payment of
the principal of, premium, if any, or interest on Notes and not applied but
remaining unclaimed by the holders of Notes for two years after the date upon
which the principal of, premium, if any, or interest on such Notes, as the case
may be, shall have become due and payable, shall be repaid to the Company by the
Trustee on demand and all liability of the Trustee shall thereupon cease with
respect to such monies; and the holder of any of the Notes shall thereafter look
only to the Company for any payment which such holder may be entitled to collect
unless an applicable abandoned property law designates another Person.

     SECTION 13.5   REINSTATEMENT.  If the Trustee or the paying agent is unable
to apply any money in accordance with Section 13.2 by reason of any order or
judgment of any court or governmental authority enjoining, restraining or
otherwise prohibiting such application, the Company's obligations

                                     -57-
<PAGE>
 
under this Indenture and the Notes shall be revived and reinstated as though no
deposit had occurred pursuant to Section 13.1 until such time as the Trustee or
the paying agent is permitted to apply all such money in accordance with Section
13.2; provided, however, that if the Company makes any payment of interest on or
principal of any Note following the reinstatement of its obligations, the
Company shall be subrogated to the rights of the holders of such Notes to
receive such payment from the money held by the Trustee or paying agent.


                                  ARTICLE XIV

        IMMUNITY OF INCORPORATORS, STOCKHOLDERS, OFFICERS AND DIRECTORS

     SECTION 14.1   INDENTURE AND NOTES SOLELY CORPORATE OBLIGATIONS. No
recourse for the payment of the principal of or premium, if any, or interest on
any Note, or for any claim based thereon or otherwise in respect thereof, and no
recourse under or upon any obligation, covenant or agreement of the Company in
this Indenture or in any supplemental indenture or in any Note, or because of
the creation of any indebtedness represented thereby, shall be had against any
incorporator, stockholder, employee, agent, officer, or director or subsidiary,
as such, past, present or future, of the Company or of any successor
corporation, either directly or through the Company or any successor
corporation, whether by virtue of any constitution, statute or rule of law, or
by the enforcement of any assessment or penalty or otherwise; it being expressly
understood that all such liability is hereby expressly waived and released as a
condition of, and as a consideration for, the execution of this Indenture and
the issue of the Notes.


                                  ARTICLE XV

                              CONVERSION OF NOTES

     SECTION 15.1    RIGHT TO CONVERT.  Subject to and upon compliance with the
provisions of this Indenture, including without limitation Article IV, the
holder of any Note shall have the right, at its option, at any time after ninety
(90) days following the original issuance of the Notes hereunder through the
close of business on the final maturity date of the Notes (except that, with
respect to any Note or portion of a Note which shall be called for redemption,
such right shall terminate, except as provided in Section 15.2 or Section 3.4,
at the close of business on the Business Day next preceding the date fixed for
redemption of such Note or portion of a Note unless the Company shall default in
payment due upon redemption thereof) to convert the principal amount of any such
Note, or any portion of such principal amount which is $1,000 or an integral
multiple thereof, into that number of fully paid and non-assessable shares of
Common Stock (as such shares shall then be constituted) obtained by dividing the
principal amount of the Note or portion thereof surrendered for conversion by
the Conversion Price in effect at such time, by surrender of the Note so to be
converted in whole or in part in the manner provided, together with any required
funds, in Section 15.2.  A Note in respect of which a holder is exercising its
option to require redemption upon a Fundamental Change pursuant to Section 3.5
may be converted only if such holder withdraws its election to exercise in
accordance with Section 3.5.  A holder of Notes is

                                     -58-
<PAGE>
 
not entitled to any rights of a holder of Common Stock until such holder has
converted his Notes to Common Stock, and only to the extent such Notes are
deemed to have been converted to Common Stock under this Article XV.

     SECTION 15.2   EXERCISE OF CONVERSION PRIVILEGE; ISSUANCE OF COMMON STOCK
ON CONVERSION; NO ADJUSTMENT FOR INTEREST OR DIVIDENDS. In order to exercise the
conversion privilege with respect to any Note in certificated form, the holder
of any such Note to be converted in whole or in part shall surrender such Note,
duly endorsed, at an office or agency maintained by the Company pursuant to
Section 5.2, accompanied by the funds, if any, required by the penultimate
paragraph of this Section 15.2, and shall give written notice of conversion in
the form provided on the Notes (or such other notice which is acceptable to the
Company) to the office or agency that the holder elects to convert such Note or
the portion thereof specified in said notice. Such notice shall also state the
name or names (with address or addresses) in which the certificate or
certificates for shares of Common Stock which shall be issuable on such
conversion shall be issued, and shall be accompanied by transfer taxes, if
required pursuant to Section 15.7. Each such Note surrendered for conversion
shall, unless the shares issuable on conversion are to be issued in the same
name as the registration of such Note, be duly endorsed by, or be accompanied by
instruments of transfer in form satisfactory to the Company duly executed by,
the holder or his duly authorized attorney.

     In order to exercise the conversion privilege with respect to any interest
in a Note in global form, the holder must complete the appropriate instruction
form for conversion pursuant to the Depository's book-entry conversion program,
deliver by book-entry delivery an interest in such Note in global form, furnish
appropriate endorsements and transfer documents if required by the Company or
the Trustee or conversion agent, and pay the funds, if any, required by this
Section 15.2 and any transfer taxes if required pursuant to Section 15.7.

     As promptly as practicable after satisfaction of the requirements for
conversion set forth above, subject to compliance with any restrictions on
transfer if shares issuable on conversion are to be issued in a name other than
that of the Noteholder (as if such transfer were a transfer of the Note or Notes
(or portion thereof) so converted), the Company shall issue and shall deliver to
such holder at the office or agency maintained by the Company for such purpose
pursuant to Section 5.2, a certificate or certificates for the number of full
shares of Common Stock issuable upon the conversion of such Note or portion
thereof in accordance with the provisions of this Article and a check or cash in
respect of any fractional interest in respect of a share of Common Stock arising
upon such conversion, as provided in Section 15.3.  In case any Note of a
denomination greater than $1,000 shall be surrendered for partial conversion,
and subject to Section 2.3, the Company shall execute and the Trustee shall
authenticate and deliver to the holder of the Note so surrendered, without
charge to him, a new Note or Notes in authorized denominations in an aggregate
principal amount equal to the unconverted portion of the surrendered Note.

     Each conversion shall be deemed to have been effected as to any such Note
(or portion thereof) on the date on which the requirements set forth above in
this Section 15.2 have been satisfied as to such Note (or portion thereof), and
the Person in whose name any certificate or certificates for shares of Common
Stock shall be issuable upon such conversion shall be deemed to have become on
said date the

                                     -59-
<PAGE>
 
holder of record of the shares represented thereby; provided, however, that any
such surrender on any date when the stock transfer books of the Company shall be
closed shall constitute the Person in whose name the certificates are to be
issued as the record holder thereof for all purposes on the next succeeding day
on which such stock transfer books are open, but such conversion shall be at the
Conversion Price in effect on the date upon which such Note shall be
surrendered.

     Any Note or portion thereof surrendered for conversion during the period
from the close of business on the record date for any interest payment date to
the close of business on the Business Day next preceding the following interest
payment date shall (unless such Note or portion thereof being converted shall
have been called for redemption on a redemption date which occurs during the
period from the close of business on such record date to the close of business
on the Business Day next preceding the following interest payment date) be
accompanied by payment, in New York Clearing House funds or other funds
acceptable to the Company, of an amount equal to the interest otherwise payable
on such interest payment date on the principal amount being converted; provided,
however, that no such payment need be made if there shall exist at the time of
conversion a default in the payment of interest on the Notes.  Except as
provided above in this Section 15.2, no payment or other adjustment shall be
made for interest accrued on any Note converted or for dividends on any shares
issued upon the conversion of such Note as provided in this Article.

     Upon the conversion of an interest in a Note in global form, the Trustee
(or other conversion agent appointed by the Company), or the Custodian at the
direction of the Trustee (or other conversion agent appointed by the Company),
shall make a notation on such Note in global form as to the reduction in the
principal amount represented thereby.  The Company shall notify the Trustee in
writing of any conversions of Notes effected through any conversion agent other
than the Trustee.

     SECTION 15.3    CASH PAYMENTS IN LIEU OF FRACTIONAL SHARES. No fractional
shares of Common Stock or scrip representing fractional shares shall be issued
upon conversion of Notes. If more than one Note shall be surrendered for
conversion at one time by the same holder, the number of full shares which shall
be issuable upon conversion shall be computed on the basis of the aggregate
principal amount of the Notes (or specified portions thereof to the extent
permitted hereby) so surrendered. If any fractional share of stock would be
issuable upon the conversion of any Note or Notes, the Company shall make an
adjustment and payment therefor in cash at the current market price thereof to
the holder of Notes. The current market price of a share of Common Stock shall
be the Closing Price on the last Business Day immediately preceding the day on
which the Notes (or specified portions thereof) are deemed to have been
converted.

     SECTION 15.4   CONVERSION PRICE. The conversion price shall be as specified
in the form of Note (herein called the "Conversion Price") attached as Exhibit A
                                                                       ---------
hereto, subject to adjustment as provided in this Article XV.

     SECTION 15.5   ADJUSTMENT OF CONVERSION PRICE. The Conversion Price shall
be adjusted from time to time by the Company as follows:

                                     -60-
<PAGE>
 
          (a) In case the Company shall hereafter pay a dividend or make a
distribution to all holders of the outstanding Common Stock in shares of Common
Stock, the Conversion Price in effect at the opening of business on the date
following the date fixed for the determination of stockholders entitled to
receive such dividend or other distribution shall be reduced by multiplying such
Conversion Price by a fraction of which the numerator shall be the number of
shares of Common Stock outstanding at the close of business on the date fixed
for such determination and the denominator shall be the sum of such number of
shares and the total number of shares constituting such dividend or other
distribution, such reduction to become effective immediately after the opening
of business on the day following the date fixed for such determination.  The
Company will not pay any dividend or make any distribution on shares of Common
Stock held in the treasury of the Company.  If any dividend or distribution of
the type described in this Section 15.5(a) is declared but not so paid or made,
the Conversion Price shall again be adjusted to the Conversion Price which would
then be in effect if such dividend or distribution had not been declared.

          (b) In case the Company shall issue rights or warrants to all holders
of its outstanding shares of Common Stock entitling them (for a period expiring
within forty-five (45) days after the date fixed for determination of
stockholders entitled to receive such rights or warrants) to subscribe for or
purchase shares of Common Stock at a price per share less than the Current
Market Price (as defined below) on the date fixed for determination of
stockholders entitled to receive such rights or warrants, the Conversion Price
shall be adjusted so that the same shall equal the price determined by
multiplying the Conversion Price in effect immediately prior to the date fixed
for determination of stockholders entitled to receive such rights or warrants by
a fraction of which the numerator shall be the number of shares of Common Stock
outstanding at the close of business on the date fixed for determination of
stockholders entitled to receive such rights and warrants plus the number of
shares which the aggregate offering price of the total number of shares so
offered would purchase at such Current Market Price, and of which the
denominator shall be the number of shares of Common Stock outstanding on the
date fixed for determination of stockholders entitled to receive such rights and
warrants plus the total number of additional shares of Common Stock offered for
subscription or purchase. Such adjustment shall be successively made whenever
any such rights and warrants are issued, and shall become effective immediately
after the opening of business on the day following the date fixed for
determination of stockholders entitled to receive such rights or warrants. To
the extent that shares of Common Stock are not delivered after the expiration of
such rights or warrants, the Conversion Price shall be readjusted to the
Conversion Price which would then be in effect had the adjustments made upon the
issuance of such rights or warrants been made on the basis of delivery of only
the number of shares of Common Stock actually delivered. In the event that such
rights or warrants are not so issued, the Conversion Price shall again be
adjusted to be the Conversion Price which would then be in effect if such date
fixed for the determination of stockholders entitled to receive such rights or
warrants had not been fixed. In determining whether any rights or warrants
entitle the holders to subscribe for or purchase shares of Common Stock at less
than such Current Market Price, and in determining the aggregate offering price
of such shares of Common Stock, there shall be taken into account any
consideration received by the Company for such rights or warrants, the value of
such consideration, if other than cash, to be determined by the Board of
Directors.

                                     -61-
<PAGE>
 
          (c) In case outstanding shares of Common Stock shall be subdivided
into a greater number of shares of Common Stock, the Conversion Price in effect
at the opening of business on the day following the day upon which such
subdivision becomes effective shall be proportionately reduced, and conversely,
in case outstanding shares of Common Stock shall be combined into a smaller
number of shares of Common Stock, the Conversion Price in effect at the opening
of business on the day following the day upon which such combination becomes
effective shall be proportionately increased, such reduction or increase, as the
case may be, to become effective immediately after the opening of business on
the day following the day upon which such subdivision or combination becomes
effective.

          (d) In case the Company shall, by dividend or otherwise, distribute to
all holders of its Common Stock shares of any class of capital stock of the
Company (other than any dividends or distributions to which Section 15.5(a)
applies) or evidences of its indebtedness or assets (including securities, but
excluding any rights or warrants referred to in Section 15.5(b), and excluding
any dividend or distribution (x) paid exclusively in cash or (y) referred to in
Section 15.5(a) (any of the foregoing hereinafter in this Section 15.5(d) called
the "Securities")), then, in each such case (unless the Company elects to
reserve such Securities for distribution to the Noteholders upon the conversion
of the Notes so that any such holder converting Notes will receive upon such
conversion, in addition to the shares of Common Stock to which such holder is
entitled, the amount and kind of such Securities which such holder would have
received if such holder had converted its Notes into Common Stock immediately
prior to the Record Date (as defined in Section 15.5(h) for such distribution of
the Securities)), the Conversion Price shall be reduced so that the same shall
be equal to the price determined by multiplying the Conversion Price in effect
on the Record Date with respect to such distribution by a fraction of which the
numerator shall be the Current Market Price per share of the Common Stock on
such Record Date less the fair market value (as determined by the Board of
Directors, whose determination shall be conclusive, and described in a
resolution of the Board if Directors) on the Record Date of the portion of the
Securities so distributed applicable to one share of Common Stock and the
denominator shall be the Current Market Price per share of the Common Stock,
such reduction to become effective immediately prior to the opening of business
on the day following such Record Date; provided, however, that in the event the
then fair market value (as so determined) of the portion of the Securities so
distributed applicable to one share of Common Stock is equal to or greater than
the Current Market Price of the Common Stock on the Record Date, in lieu of the
foregoing adjustment, adequate provision shall be made so that each Noteholder
shall have the right to receive upon conversion the amount of Securities such
holder would have received had such holder converted each Note on the Record
Date. In the event that such dividend or distribution is not so paid or made,
the Conversion Price shall again be adjusted to be the Conversion Price which
would then be in effect if such dividend or distribution had not been declared.
If the Board of Directors determines the fair market value of any distribution
for purposes of this Section 15.5(d) by reference to the actual or when issued
trading market for any securities, it must in doing so consider the prices in
such market over the same period used in computing the Current Market Price of
the Common Stock.

     Under the provisions of the Company's Share Purchase Rights Plan, dated as
of October 8, 1997, between the Company and The First National Bank of Boston
(the "Rights Plan"), upon conversion of the Notes into Common Stock to the
extent that such Rights Plan is still in effect upon such conversion, the
holders will receive, in addition to the Common Stock, the Rights described
therein (whether or not

                                     -62-
<PAGE>
 
the Rights have separated at the time of conversion), subject to certain
exceptions set forth in the Rights Plan.

     Rights or warrants distributed by the Company to all holders of Common
Stock entitling the holders thereof to subscribe for or purchase shares of the
Company's capital stock (either initially or under certain circumstances), which
rights or warrants, until the occurrence of a specified event or events
("Trigger Event"):  (i) are deemed to be transferred with such shares of Common
Stock; (ii) are not exercisable; and (iii) are also issued in respect of future
issuances of Common Stock, shall be deemed not to have been distributed for
purposes of this Section 15.5 (and no adjustment to the Conversion Price under
this Section 15.5 will be required) until the occurrence of the earliest Trigger
Event, whereupon such rights and warrants shall be deemed to have been
distributed and an appropriate adjustment (if any is required) to the Conversion
Price shall be made under this Section 15.5(d).  If any such right or warrant,
including any such existing rights or warrants distributed prior to the date of
this Indenture, are subject to events, upon the occurrence of which such rights
or warrants become exercisable to purchase different securities, evidences of
indebtedness or other assets, then the date of the occurrence of any and each
such event shall be deemed to be the date of distribution and record date with
respect to new rights or warrants with such rights (and a termination or
expiration of the existing rights or warrants without exercise by any of the
holders thereof).  In addition, in the event of any distribution (or deemed
distribution) of rights or warrants, or any Trigger Event or other event (of the
type described in the preceding sentence) with respect thereto that was counted
for purposes of calculating a distribution amount for which an adjustment to the
Conversion Price under this Section 15.5 was made, (1) in the case of any such
rights or warrants which shall all have been redeemed or repurchased without
exercise by any holders thereof, the Conversion Price shall be readjusted upon
such final redemption or repurchase to give effect to such distribution or
Trigger Event, as the case may be, as though it were a cash distribution, equal
to the per share redemption or repurchase price received by a holder or holders
of Common Stock with respect to such rights or warrants (assuming such holder
had retained such rights or warrants), made to all holders of Common Stock as of
the date of such redemption or repurchase, and (2) in the case of such rights or
warrants which shall have expired or been terminated without exercise by any
holders thereof, the Conversion Price shall be readjusted as if such rights and
warrants had not been issued.

     For purposes of this Section 15.5(d) and Sections 15.5(a) and (b), any
dividend or distribution to which this Section 15.5(d) is applicable that also
includes shares of Common Stock, or rights or warrants to subscribe for or
purchase shares of Common Stock (or both), shall be deemed instead to be (1) a
dividend or distribution of the evidences of indebtedness, assets or shares of
capital stock other than such shares of Common Stock or rights or warrants (and
any Conversion Price reduction required by this Section 15.5(d) with respect to
such dividend or distribution shall then be made) immediately followed by (2) a
dividend or distribution of such shares of Common Stock or such rights or
warrants (and any further Conversion Price reduction required by Sections
15.5(a) and (b) with respect to such dividend or distribution shall then be
made), except (A) the Record Date of such dividend or distribution shall be
substituted as "the date fixed for the determination of stockholders entitled to
receive such dividend or other distribution" and "the date fixed for such
determination" within the meaning of Sections 15.5(a) and (b) and (B) any shares
of Common Stock included in such dividend or distribution shall not be

                                     -63-
<PAGE>
 
deemed "outstanding at the close of business on the date fixed for such
determination" within the meaning of Section 15.5(a).

          (e) In case the Company shall, by dividend or otherwise, distribute to
all holders of its Common Stock cash (excluding (x) any quarterly cash dividend
on the Common Stock to the extent the aggregate cash dividend per share of
Common Stock in any fiscal quarter does not exceed the greater of (A) the amount
per share of Common Stock of the next preceding quarterly cash dividend on the
Common Stock to the extent that such preceding quarterly dividend did not
require any adjustment of the Conversion Price pursuant to this Section 15.5(e)
(as adjusted to reflect subdivisions or combinations of the Common Stock), and
(B) 3.75% of the arithmetic average of the Closing Price (determined as set
forth in Section 15.5(h)) during the ten Trading Days (as defined in Section
15.5(h)) immediately prior to the date of declaration of such dividend, and (y)
any dividend or distribution in connection with the liquidation, dissolution or
winding up of the Company, whether voluntary or involuntary), then, in such
case, the Conversion Price shall be reduced so that the same shall equal the
price determined by multiplying the Conversion Price in effect immediately prior
to the close of business on such Record Date by a fraction of which the
numerator shall be the Current Market Price of the Common Stock on the record
date less the amount of cash so distributed (and not excluded as provided above)
applicable to one share of Common Stock and the denominator shall be such
Current Market Price of the Common Stock, such reduction to be effective
immediately prior to the opening of business on the day following the record
date; provided, however, that in the event the portion of the cash so
distributed applicable to one share of Common Stock is equal to or greater than
the Current Market Price of the Common Stock on the Record Date, in lieu of the
foregoing adjustment, adequate provision shall be made so that each Noteholder
shall have the right to receive upon conversion the amount of cash such holder
would have received had such holder converted each Note on the Record Date. In
the event that such dividend or distribution is not so paid or made, the
Conversion Price shall again be adjusted to be the Conversion Price which would
then be in effect if such dividend or distribution had not been declared. If any
adjustment is required to be made as set forth in this Section 15.5(e) as a
result of a distribution that is a quarterly dividend, such adjustment shall be
based upon the amount by which such distribution exceeds the amount of the
quarterly cash dividend permitted to be excluded pursuant hereto. If an
adjustment is required to be made as set forth in this Section 15.5(e) above as
a result of a distribution that is not a quarterly dividend, such adjustment
shall be based upon the full amount of the distribution.

          (f) In case a tender or exchange offer made by the Company or any
Subsidiary for all or any portion of the Common Stock shall expire and such
tender or exchange offer (as amended upon the expiration thereof) shall require
the payment to stockholders of consideration per share of Common Stock having a
fair market value (as determined by the Board of Directors, whose determination
shall be conclusive and described in a resolution of the Board if Directors)
that as of the last time (the "Expiration Time") tenders or exchanges may be
made pursuant to such tender or exchange offer (as it may be amended) that
exceeds the Current Market Price of the Common Stock on the Trading Day next
succeeding the Expiration Time, the Conversion Price shall be reduced so that
the same shall equal the price determined by multiplying the Conversion Price in
effect immediately prior to the Expiration Time by a fraction of which the
numerator shall be the number of shares of Common Stock outstanding (including
any tendered or exchanged shares) on the Expiration Time multiplied by the
Current Market Price of the Common Stock on the Trading Day next succeeding the
Expiration Time

                                     -64-
<PAGE>
 
and the denominator shall be the sum of (x) the fair market value (determined as
aforesaid) of the aggregate consideration payable to stockholders based on the
acceptance (up to any maximum specified in the terms of the tender or exchange
offer) of all shares validly tendered or exchanged and not withdrawn as of the
Expiration Time (the shares deemed so accepted, up to any such maximum, being
referred to as the "Purchased Shares") and (y) the product of the number of
shares of Common Stock outstanding (less any Purchased Shares) on the Expiration
Time and the Current Market Price of the Common Stock on the Trading Day next
succeeding the Expiration Time, such reduction to become effective immediately
prior to the opening of business on the day following the Expiration Time.  In
the event that the Company is obligated to purchase shares pursuant to any such
tender or exchange offer, but the Company is permanently prevented by applicable
law from effecting any such purchases or all such purchases are rescinded, the
Conversion Price shall again be adjusted to be the Conversion Price which would
then be in effect if such tender or exchange offer had not been made.

          (g) In case of a tender or exchange offer made by a Person other than
the Company or any Subsidiary for an amount which increases the offeror's
ownership of Common Stock to more than twenty-five percent (25%) of the Common
Stock outstanding and shall involve the payment by such Person of consideration
per share of Common Stock having a fair market value (as determined by the Board
of Directors, whose determination shall be conclusive, and described in a
resolution of the Board of Directors) at the last time (the "Offer Expiration
Time") tenders or exchanges may be made pursuant to such tender or exchange
offer (as it shall have been amended) that exceeds the Current Market Price of
the Common Stock on the Trading Day next succeeding the Offer Expiration Time,
and in which, as of the Offer Expiration Time the Board of Directors is not
recommending rejection of the offer, the Conversion Price shall be reduced so
that the same shall equal the price determined by multiplying the Conversion
Price in effect immediately prior to the Offer Expiration Time by a fraction of
which the numerator shall be the number of shares of Common Stock outstanding
(including any tendered or exchanged shares) on the Offer Expiration Time
multiplied by the Current Market Price of the Common Stock on the Trading Day
next succeeding the Offer Expiration Time and the denominator shall be the sum
of (x) the fair market value (determined as aforesaid) of the aggregate
consideration payable to stockholders based on the acceptance (up to any maximum
specified in the terms of the tender or exchange offer) of all shares validly
tendered or exchanged and not withdrawn as of the Offer Expiration Time (the
shares deemed so accepted, up to any such maximum, being referred to as the
"Accepted Purchased Shares") and (y) the product of the number of shares of
Common Stock outstanding (less any Accepted Purchased Shares) on the Offer
Expiration Time and the Current Market Price of the Common Stock on the Trading
Day next succeeding the Offer Expiration Time, such reduction to become
effective immediately prior to the opening of business on the day following the
Offer Expiration Time. In the event that such Person is obligated to purchase
shares pursuant to any such tender or exchange offer, but such Person is
permanently prevented by applicable law from effecting any such purchases or all
such purchases are rescinded, the Conversion Price shall again be adjusted to be
the Conversion Price which would then be in effect if such tender or exchange
offer had not been made. Notwithstanding the foregoing, the adjustment described
in this Section 15.5(g) shall not be made if, as of the Offer Expiration Time,
the offering documents with respect to such offer disclose a plan or intention
to cause the Company to engage in any transaction described in Article XII.

                                     -65-
<PAGE>
 
          (h) For purposes of this Section 15.5, the following terms shall have
the meaning indicated:

                (1) "Closing Price" with respect to any securities on any day
shall mean the closing sale price regular way on such day or, in case no such
sale takes place on such day, the average of the reported closing bid and asked
prices, regular way, in each case on the New York Stock Exchange, or, if such
security is not listed or admitted to trading on such Exchange, on the principal
national security exchange or quotation system on which such security is quoted
or listed or admitted to trading, or, if not quoted or listed or admitted to
trading on any national securities exchange or quotation system, the average of
the closing bid and asked prices of such security on the over-the-counter market
on the day in question as reported by the National Quotation Bureau
Incorporated, or a similar generally accepted reporting service, or if not so
available, in such manner as furnished by any New York Stock Exchange member
firm selected from time to time by the Board of Directors for that purpose, or a
price determined in good faith by the Board of Directors or, to the extent
permitted by applicable law, a duly authorized committee thereof, whose
determination shall be conclusive.

                (2) "Current Market Price" shall mean the average of the daily
Closing Prices per share of Common Stock for the ten consecutive Trading Days
immediately prior to the date in question; provided, however, that (1) if the
"ex" date (as hereinafter defined) for any event (other than the issuance or
distribution or Fundamental Change requiring such computation) that requires an
adjustment to the Conversion Price pursuant to Section 15.5(a), (b), (c), (d),
(e), (f) or (g) occurs during such ten consecutive Trading Days, the Closing
Price for each Trading Day prior to the "ex" date for such other event shall be
adjusted by multiplying such Closing Price by the same fraction by which the
Conversion Price is so required to be adjusted as a result of such other event,
(2) if the "ex" date for any event (other than the issuance, distribution or
Fundamental Change requiring such computation) that requires an adjustment to
the Conversion Price pursuant to Section 15.5(a), (b), (c), (d), (e), (f) or (g)
occurs on or after the "ex" date for the issuance or distribution requiring such
computation and prior to the day in question, the Closing Price for each Trading
Day on and after the "ex" date for such other event shall be adjusted by
multiplying such Closing Price by the reciprocal of the fraction by which the
Conversion Price is so required to be adjusted as a result of such other event,
and (3) if the "ex" date for the issuance, distribution or Fundamental Change
requiring such computation is prior to the day in question, after taking into
account any adjustment required pursuant to clause (1) or (2) of this proviso,
the Closing Price for each Trading Day on or after such "ex" date shall be
adjusted by adding thereto the amount of any cash and the fair market value (as
determined by the Board of Directors or, to the extent permitted by applicable
law, a duly authorized committee thereof in a manner consistent with any
determination of such value for purposes of Section 15.5(d), (f) or (g), whose
determination shall be conclusive and described in a resolution of the Board of
Directors or such duly authorized committee thereof, as the case may be) of the
evidences of indebtedness, shares of capital stock or assets being distributed
applicable to one share of Common Stock as of the close of business on the day
before such "ex" date. For purposes of any computation under Section 15.5(f) or
(g), the Current Market Price of the Common Stock on any date shall be deemed to
be the average of the daily Closing Prices per share of Common Stock for such
day and the next two succeeding Trading Days; provided, however, that if the
"ex" date for any event (other than the tender or exchange offer requiring such
computation) that requires an adjustment to the Conversion Price pursuant to
Section 15.5(a), (b), (c), (d), (e), (f) or (g)

                                     -66-
<PAGE>
 
occurs on or after the Expiration Time or Offer Expiration Time, as the case may
be, for the tender or exchange offer requiring such computation and prior to the
day in question, the Closing Price for each Trading Day on and after the "ex"
date for such other event shall be adjusted by multiplying such Closing Price by
the reciprocal of the fraction by which the Conversion Price is so required to
be adjusted as a result of such other event.  For purposes of this paragraph,
the term "ex" date, (1) when used with respect to any issuance or distribution,
means the first date on which the Common Stock trades regular way on the
relevant exchange or in the relevant market from which the Closing Price was
obtained without the right to receive such issuance or distribution, (2) when
used with respect to any subdivision or combination of shares of Common Stock,
means the first date on which the Common Stock trades regular way on such
exchange or in such market after the time at which such subdivision or
combination becomes effective, and (3) when used with respect to any tender or
exchange offer means the first date on which the Common Stock trades regular way
on such exchange or in such market after the Offer Expiration Time of such
offer.

                (3) "fair market value" shall mean the amount which a willing
buyer would pay a willing seller in an arm's length transaction.

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

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

          (i) The Company may make such reductions in the Conversion Price, in
addition to those required by Sections 15.5 (a), (b), (c), (d), (e), (f) or (g)
as the Board of Directors considers to be advisable to avoid or diminish any
income tax to holders of Common Stock or rights to purchase Common Stock
resulting from any dividend or distribution of stock (or rights to acquire
stock) or from any event treated as such for income tax purposes.

     To the extent permitted by applicable law, the Company from time to time
may reduce the Conversion Price by any amount for any period of time if the
period is at least twenty (20) days, the reduction is irrevocable during the
period and the Board of Directors shall have made a determination that such
reduction would be in the best interests of the Company, which determination
shall be conclusive.  Whenever the Conversion Price is reduced pursuant to the
preceding sentence, the Company shall mail to holders of record of the Notes a
notice of the reduction at least fifteen (15) days prior to the

                                     -67-
<PAGE>
 
date the reduced Conversion Price takes effect, and such notice shall state the
reduced Conversion Price and the period during which it will be in effect.

          (j) No adjustment in the Conversion Price shall be required unless
such adjustment would require an increase or decrease of at least one percent
(1%) in such price; provided, however, that any adjustments which by reason of
this Section 15.5(j) are not required to be made shall be carried forward and
taken into account in any subsequent adjustment. All calculations under this
Article XV shall be made by the Company and shall be made to the nearest cent or
to the nearest one-hundredth (1/100) of a share, as the case may be. No
adjustment need be made for rights to purchase Common Stock pursuant to a
Company plan for reinvestment of dividends or interest. To the extent the Notes
become convertible into cash, assets, property or securities (other than capital
stock of the Company), no adjustment need be made thereafter as to the cash,
assets, property or such securities. Interest will not accrue on the cash.

          (k) Whenever the Conversion Price is adjusted as herein provided, the
Company shall promptly file with the Trustee and any conversion agent other than
the Trustee an Officers' Certificate setting forth the Conversion Price after
such adjustment and setting forth a brief statement of the facts requiring such
adjustment.  Unless and until a Responsible Officer of the Trustee shall have
received such Officers' Certificate, the Trustee shall not be deemed to have
knowledge of any adjustment of the Conversion Price and may assume without
inquiry that the last Conversion Price of which it has knowledge is still in
effect.  Promptly after delivery of such certificate, the Company shall prepare
a notice of such adjustment of the Conversion Price setting forth the adjusted
Conversion Price and the date on which each adjustment becomes effective and
shall mail such notice of such adjustment of the Conversion Price to the holder
of each Note at his last address appearing on the Note register provided for in
Section 2.5 of this Indenture, within twenty (20) days after execution thereof.
Failure to deliver such notice shall not affect the legality or validity of any
such adjustment.

          (l) In any case in which this Section 15.5 provides that an adjustment
shall become effective immediately after a record date for an event, the Company
may defer until the occurrence of such event (i) issuing to the holder of any
Note converted after such record date and before the occurrence of such event
the additional shares of Common Stock issuable upon such conversion by reason of
the adjustment required by such event over and above the Common Stock issuable
upon such conversion before giving effect to such adjustment and (ii) paying to
such holder any amount in cash in lieu of any fraction pursuant to Section 15.3.

          (m) For purposes of this Section 15.5, the number of shares of Common
Stock at any time outstanding shall not include shares held in the treasury of
the Company but shall include shares issuable in respect of scrip certificates
issued in lieu of fractions of shares of Common Stock.  The Company will not pay
any dividend or make any distribution on shares of Common Stock held in the
treasury of the Company.

     SECTION 15.6   EFFECT OF RECLASSIFICATION, CONSOLIDATION, MERGER OR SALE.
If any of the following events occur, namely (i) any reclassification or change
of the outstanding shares of Common Stock (other than a subdivision or
combination to which Section 15.5(c) applies), (ii) any consolidation,

                                     -68-
<PAGE>
 
merger or combination of the Company with another Person as a result of which
holders of Common Stock shall be entitled to receive stock, securities or other
property or assets (including cash) with respect to or in exchange for such
Common Stock, or (iii) any sale or conveyance of all or substantially all of the
properties and assets of the Company to any other Person as a result of which
holders of Common Stock shall be entitled to receive stock, securities or other
property or assets (including cash) with respect to or in exchange for such
Common Stock, then the Company or the successor or purchasing Person, as the
case may be, shall execute with the Trustee a supplemental indenture (which
shall comply with the Trust Indenture Act as in force at the date of execution
of such supplemental indenture) providing that such Note shall be convertible
into the kind and amount of shares of stock, securities or other property or
assets (including cash) receivable upon such reclassification, change,
consolidation, merger, combination, sale or conveyance by a holder of a number
of shares of Common Stock issuable upon conversion of such Notes (assuming, for
such purposes, a sufficient number of authorized shares of Common Stock
available to convert all such Notes) immediately prior to such reclassification,
change, consolidation, merger, combination, sale or conveyance assuming such
holder of Common Stock did not exercise his rights of election, if any, as to
the kind or amount of securities, cash or other property receivable upon such
reclassification, change, consolidation, merger, combination, sale or conveyance
(provided that, if the kind or amount of stock, securities or other property or
assets (including cash) receivable upon such reclassification, change,
consolidation, merger, combination, sale or conveyance is not the same for each
share of Common Stock in respect of which such rights of election shall not have
been exercised ("nonelecting share")), then for the purposes of this Section
15.6 the kind and amount of securities, cash or other property receivable upon
such reclassification, change, consolidation, merger, combination, sale or
conveyance for each non-electing share shall be deemed to be the kind and amount
so receivable per share by a plurality of the non-electing shares.  Such
supplemental indenture shall provide for adjustments which shall be as nearly
equivalent as may be practicable to the adjustments provided for in this
Article.

     The Company shall cause notice of the execution of such supplemental
indenture to be mailed to each holder of Notes, at its address appearing on the
Note register provided for in Section 2.5 of this Indenture, within twenty (20)
days after execution thereof.  Failure to deliver such notice shall not affect
the legality or validity of such supplemental indenture.

     The above provisions of this Section shall similarly apply to successive
reclassifications, changes, consolidations, mergers, combinations, sales and
conveyances.

     If this Section 15.6 applies to any event or occurrence, Section 15.5 shall
not apply.

     SECTION 15.7   TAXES ON SHARES ISSUED.  The issue of stock certificates on
conversions of Notes shall be made without charge to the converting Noteholder
for any tax in respect of the issue thereof.  The Company shall not, however, be
required to pay any tax which may be payable in respect of any transfer involved
in the issue and delivery of stock in any name other than that of the holder of
any Note converted, and the Company shall not be required to issue or deliver
any such stock certificate unless and until the Person or Persons requesting the
issue thereof shall have paid to the Company the amount of such tax or shall
have established to the satisfaction of the Company that such tax has been paid.

                                     -69-
<PAGE>
 
     SECTION 15.8    RESERVATION OF SHARES; SHARES TO BE FULLY PAID; COMPLIANCE
WITH GOVERNMENTAL REQUIREMENTS; LISTING OF COMMON STOCK. The Company shall
provide, free from preemptive rights, out of its authorized but unissued shares
or shares held in treasury, sufficient shares of Common Stock to provide for the
conversion of the Notes from time to time as such Notes are presented for
conversion.

     Before taking any action which would cause an adjustment reducing the
Conversion Price below the then par value, if any, of the shares of Common Stock
issuable upon conversion of the Notes, the Company will take all corporate
action which may, in the opinion of its counsel, be necessary in order that the
Company may validly and legally issue shares of such Common Stock at such
adjusted Conversion Price.

     The Company covenants that all shares of Common Stock which may be issued
upon conversion of Notes will upon issue be fully paid and non-assessable by the
Company and free from all taxes, liens and charges with respect to the issue
thereof.

     The Company covenants that if any shares of Common Stock to be provided for
the purpose of conversion of Notes hereunder require registration with or
approval of any governmental authority under any federal or state law before
such shares may be validly issued upon conversion, the Company will in good
faith and as expeditiously as possible endeavor to secure such registration or
approval, as the case may be.

     The Company further covenants that if at any time the Common Stock shall be
listed on the Nasdaq National Market or any other national securities exchange
or automated quotation system the Company will, if permitted by the rules of
such exchange or automated quotation system, list and keep listed, so long as
the Common Stock shall be so listed on such exchange or automated quotation
system, all Common Stock issuable upon conversion of the Notes; provided,
however, that if rules of such exchange or automated quotation system permit the
Company to defer the listing of such Common Stock until the first conversion of
the Notes into Common Stock in accordance with the provisions of this Indenture,
the Company covenants to list such Common Stock issuable upon conversion of the
Notes in accordance with the requirements of such exchange or automated
quotation system at such time.

     SECTION 15.9   RESPONSIBILITY OF TRUSTEE. The Trustee and any other
conversion agent shall not at any time be under any duty or responsibility to
any holder of Notes to determine the Conversion Price or whether any facts exist
which may require any adjustment of the Conversion Price, or with respect to the
nature or extent or calculation of any such adjustment when made, or with
respect to the method employed, or herein or in any supplemental indenture
provided to be employed, in making the same. The Trustee and any other
conversion agent shall not be accountable with respect to the validity or value
(or the kind or amount) of any shares of Common Stock, or of any securities or
property, which may at any time be issued or delivered upon the conversion of
any Note; and the Trustee and any other conversion agent make no representations
with respect thereto. Neither the Trustee nor any conversion agent shall be
responsible for any failure of the Company to issue, transfer or deliver any
shares of Common Stock or stock certificates or other securities or property or
cash upon the surrender of any Note for the purpose of conversion or to comply
with any of the duties, responsibilities or covenants of

                                     -70-
<PAGE>
 
the Company contained in this Article.  Without limiting the generality of the
foregoing, neither the Trustee nor any conversion agent shall be under any
responsibility to determine the correctness of any provisions contained in any
supplemental indenture entered into pursuant to Section 15.6 relating either to
the kind or amount of shares of stock or securities or property (including cash)
receivable by Noteholders upon the conversion of their Notes after any event
referred to in such Section 15.6 or to any adjustment to be made with respect
thereto, but, subject to the provisions of Section 8.1, may accept as conclusive
evidence of the correctness of any such provisions, and shall be protected in
relying upon, the Officers' Certificate (which the Company shall be obligated to
file with the Trustee prior to the execution of any such supplemental indenture)
with respect thereto.

     SECTION 15.10    NOTICE TO HOLDERS PRIOR TO CERTAIN ACTIONS.  In case:

          (a) the Company shall declare a dividend (or any other distribution)
on its Common Stock that would require an adjustment in the Conversion Price
pursuant to Section 15.5; or

          (b) the Company shall authorize the granting to the holders of all or
substantially all of its Common Stock of rights or warrants to subscribe for or
purchase any share of any class or any other rights or warrants; or

          (c) of any reclassification or reorganization of the Common Stock of
the Company (other than a subdivision or combination of its outstanding Common
Stock, or a change in par value, or from par value to no par value, or from no
par value to par value), or of any consolidation or merger to which the Company
is a party and for which approval of any stockholders of the Company is
required, or of the sale or transfer of all or substantially all of the assets
of the Company or any Significant Subsidiary; or

          (d) of the voluntary or involuntary dissolution, liquidation or
winding up of the Company or any Significant Subsidiary;

the Company shall cause to be filed with the Trustee and to be mailed to each
holder of Notes at his address appearing on the Note register provided for in
Section 2.5 of this Indenture, as promptly as possible but in any event at least
fifteen (15) days prior to the applicable date hereinafter specified, a notice
stating (x) the date on which a record is to be taken for the purpose of such
dividend, distribution or rights or warrants, or, if a record is not to be
taken, the date as of which the holders of Common Stock of record to be entitled
to such dividend, distribution or rights are to be determined, or (y) the date
on which such reclassification, consolidation, merger, sale, transfer,
dissolution, liquidation or winding up is expected to become effective or occur,
and the date as of which it is expected that holders of Common Stock of record
shall be entitled to exchange their Common Stock for securities or other
property deliverable upon such reclassification, consolidation, merger, sale,
transfer, dissolution, liquidation or winding up.  Failure to give such notice,
or any defect therein, shall not affect the legality or validity of such
dividend, distribution, reclassification, consolidation, merger, sale, transfer,
dissolution, liquidation or winding up.



                                     -71-
<PAGE>
 
                                  ARTICLE XVI

                           MISCELLANEOUS PROVISIONS

     SECTION 16.1   PROVISIONS BINDING ON COMPANY'S SUCCESSORS. All the
covenants, stipulations, promises and agreements by the Company contained in
this Indenture shall bind its successors and assigns whether so expressed or
not.

     SECTION 16.2   OFFICIAL ACTS BY SUCCESSOR CORPORATION. Any act or
proceeding by any provision of this Indenture authorized or required to be done
or performed by any board, committee or officer of the Company shall and may be
done and performed with like force and effect by the like board, committee or
officer of any Person that shall at the time be the lawful sole successor of the
Company.

     SECTION 16.3   ADDRESSES FOR NOTICES, ETC. Any notice or demand which by
any provision of this Indenture is required or permitted to be given or served
by the Trustee or by the holders of Notes on the Company shall be deemed to have
been sufficiently given or made, for all purposes, if given or served by being
deposited postage prepaid by registered or certified mail in a post office
letter box addressed (until another address is filed by the Company with the
Trustee) to Aviron, 297 North Bernardo Avenue, Mountain View, California 94043,
Attention: Chief Financial Officer. Any notice, direction, request or demand
hereunder to or upon the Trustee shall be deemed to have been sufficiently given
or made, for all purposes, if given or served by being deposited postage prepaid
by registered or certified mail in a post office letter box addressed to the
Corporate Trust Office, which office is, at the date as of which this Indenture
is dated, located at 140 Broadway, 12th Floor, New York, New York, 10005,
Attention: Corporate Trust Department (Aviron, 5 3/4% Convertible Subordinated
Notes due 2005).

     The Trustee, by notice to the Company, may designate additional or
different addresses for subsequent notices or communications.

     Any notice or communication mailed to a Noteholder shall be mailed to him
by first class mail, postage prepaid, at his address as it appears on the Note
register and shall be sufficiently given to him if so mailed within the time
prescribed.

     Failure to mail a notice or communication to a Noteholder or any defect in
it shall not affect its sufficiency with respect to other Noteholders.  If a
notice or communication is mailed in the manner provided above, it is duly
given, whether or not the addressee receives it.

     SECTION 16.4   GOVERNING LAW. This Indenture and each Note shall be deemed
to be a contract made under the laws of New York, and for all purposes shall be
construed in accordance with the laws of New York.

     SECTION 16.5   EVIDENCE OF COMPLIANCE WITH CONDITIONS PRECEDENT;
CERTIFICATES TO TRUSTEE. Upon any application or demand by the Company to the
Trustee to take any action under any of the provisions of this Indenture, the
Company shall furnish to the Trustee an Officers' Certificate stating that

                                     -72-
<PAGE>
 
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 have been complied
with.

     Each certificate or opinion provided for in this Indenture and delivered to
the Trustee with respect to compliance with a condition or covenant provided for
in this Indenture shall include (1) a statement that the person making such
certificate or opinion has read such covenant or condition; (2) a brief
statement as to the nature and scope of the examination or investigation upon
which the statement or opinion contained in such certificate or opinion is
based; (3) a statement that, in the opinion of such person, he has made such
examination or investigation as is necessary to enable him to express an
informed opinion as to whether or not such covenant or condition has been
complied with; and (4) a statement as to whether or not, in the opinion of such
person, such condition or covenant has been complied with.

     SECTION 16.6   LEGAL HOLIDAYS.  In any case where the date of maturity of
interest on or principal of the Notes or the date fixed for redemption of any
Note will not be a Business Day, then payment of such interest on or principal
of the Notes need not be made on such date, but may be made on the next
succeeding Business Day with the same force and effect as if made on the date of
maturity or the date fixed for redemption, and no interest shall accrue for the
period from and after such date.

     SECTION 16.7   TRUST INDENTURE ACT. This Indenture is hereby made subject
to, and shall be governed by, the provisions of the Trust Indenture Act required
to be part of and to govern indentures qualified under the Trust Indenture Act;
provided, however, that, unless otherwise required by law, notwithstanding the
foregoing, this Indenture and the Notes issued hereunder shall not be subject to
the provisions of subsections (a)(1), (a)(2), and (a)(3) of Section 314 of the
Trust Indenture Act as now in effect or as hereafter amended or modified;
provided, further, that this Section 16.7 shall not require this Indenture or
the Trustee to be qualified under the Trust Indenture Act prior to the time such
qualification is in fact required under the terms of the Trust Indenture Act,
nor shall it constitute any admission or acknowledgment by any party to such
supplemental indenture that any such qualification is required prior to the time
such qualification is in fact required under the terms of the Trust Indenture
Act. If any provision hereof limits, qualifies or conflicts with another
provision hereof which is required to be included in an indenture qualified
under the Trust Indenture Act, such required provision shall control.

     SECTION 16.8   NO SECURITY INTEREST CREATED. Nothing in this Indenture or
in the Notes, expressed or implied, shall be construed to constitute a security
interest under the Uniform Commercial Code or similar legislation, as now or
hereafter enacted and in effect, in any jurisdiction where property of the
Company or its subsidiaries is located.

     SECTION 16.9   BENEFITS OF INDENTURE.  Nothing in this Indenture or in the
Notes, expressed or implied, shall give to any Person, other than the parties
hereto, any paying agent, any authenticating agent, any Note registrar and their
successors hereunder, the holders of Notes and the holders of Senior
Indebtedness, any benefit or any legal or equitable right, remedy or claim under
this Indenture.


                                     -73-
<PAGE>
 
    SECTION 16.10    TABLE OF CONTENTS, HEADINGS, ETC. The table of contents and
the titles and headings of the articles and sections of this Indenture have been
inserted for convenience of reference only, are not to be considered a part
hereof, and shall in no way modify or restrict any of the terms or provisions
hereof.

    SECTION 16.11    AUTHENTICATING AGENT. The Trustee may appoint an
authenticating agent which shall be authorized to act on its behalf and subject
to its direction in the authentication and delivery of Notes in connection with
the original issuance thereof and transfers and exchanges of Notes hereunder,
including under Sections 2.4, 2.5, 2.6, 2.7, 3.3 and 3.5, as fully to all
intents and purposes as though the authenticating agent had been expressly
authorized by this Indenture and those Sections to authenticate and deliver
Notes. For all purposes of this Indenture, the authentication and delivery of
Notes by the authenticating agent shall be deemed to be authentication and
delivery of such Notes "by the Trustee" and a certificate of authentication
executed on behalf of the Trustee by an authenticating agent shall be deemed to
satisfy any requirement hereunder or in the Notes for the Trustee's certificate
of authentication. Such authenticating agent shall at all times be a Person
eligible to serve as trustee hereunder pursuant to Section 8.9.

     Any corporation into which any authenticating agent may be merged or
converted or with which it may be consolidated, or any corporation resulting
from any merger, consolidation or conversion to which any authenticating agent
shall be a party, or any corporation succeeding to the corporate trust business
of any authenticating agent, shall be the successor of the authenticating agent
hereunder, if such successor corporation is otherwise eligible under this
Section 16.11, without the execution or filing of any paper or any further act
on the part of the parties hereto or the authenticating agent or such successor
corporation.

     Any authenticating agent may at any time resign by giving written notice of
resignation to the Trustee and to the Company.  The Trustee may at any time
terminate the agency of any 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
any authenticating agent shall cease to be eligible under this Section, the
Trustee shall either promptly appoint a successor authenticating agent or itself
assume the duties and obligations of the former authenticating agent under this
Indenture, and upon such appointment of a successor authenticating agent, if
made, shall give written notice of such appointment of a successor
authenticating agent to the Company and shall mail notice of such appointment of
a successor authenticating agent to all holders of Notes as the names and
addresses of such holders appear on the Note register.

     The Company agrees to pay to the authenticating agent from time to time
such reasonable compensation for its services as shall be agreed in writing
between the Company and the authenticating agent.

     The provisions of Sections 8.2, 8.3, 8.4, 9.3 and this Section 16.11 shall
be applicable to any authenticating agent.


                                     -74-
<PAGE>
 
    SECTION 16.12    EXECUTION IN COUNTERPARTS. 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 and the same instrument.

     Marine Midland Bank hereby accepts the trusts in this Indenture declared
and provided, upon the terms and conditions hereinabove set forth.


                                     -75-
<PAGE>
 
     IN WITNESS WHEREOF, the parties hereto have caused this Indenture to be
duly executed.

                              AVIRON


                                    /s/ J. Leighton Read, M.D.      
                              By:_________________________________________

                                           J. Leighton Read, M.D.            
                                    Name:______________________________

                                           Chief Executive Officer      
                                    Title:_____________________________



                              MARINE MIDLAND BANK,
                              as Trustee



                                    /s/ Marcia Markowski      
                              By:_________________________________________

                                           Marcia Markowski      
                                    Name:___________________________

                                    Title:__________________________



                                     -76-
<PAGE>
 
                                   EXHIBIT A

[For Global Note only:

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY (55 WATER STREET, NEW YORK, NEW YORK) (THE
"DEPOSITARY," WHICH TERM INCLUDES ANY SUCCESSOR DEPOSITARY FOR THE CERTIFICATES)
TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT,
AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH
OTHER NAME AS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DEPOSITARY AND ANY
PAYMENT HEREON IS MADE TO CEDE & CO. (OR TO SUCH OTHER ENTITY AS IS REQUESTED BY
AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITARY), ANY TRANSFER, PLEDGE, OR OTHER
USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INSOFAR AS THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.]

THE NOTE EVIDENCED HEREBY HAS NOT BEEN REGISTERED UNDER THE U.S. SECURITIES ACT
OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR ANY STATE SECURITIES LAWS, AND,
ACCORDINGLY, MAY NOT BE OFFERED OR SOLD EXCEPT AS SET FORTH IN THE FOLLOWING
SENTENCE.  BY ITS ACQUISITION HEREOF, THE HOLDER (1) REPRESENTS THAT (A) IT IS A
"QUALIFIED INSTITUTIONAL BUYER" (AS DEFINED IN RULE 144A UNDER THE SECURITIES
ACT) OR (B) IT IS AN INSTITUTIONAL "ACCREDITED INVESTOR" (AS DEFINED IN RULE
501(A)(1), (2), (3) OR (7) UNDER THE SECURITIES ACT) ("INSTITUTIONAL ACCREDITED
INVESTOR"); (2) AGREES THAT IT WILL NOT, PRIOR TO EXPIRATION OF THE HOLDING
PERIOD APPLICABLE TO SALES OF THE NOTE EVIDENCED HEREBY UNDER RULE 144(K) UNDER
THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION), RESELL OR OTHERWISE TRANSFER
THE NOTE EVIDENCED HEREBY OR THE COMMON STOCK ISSUABLE UPON CONVERSION OF SUCH
NOTE EXCEPT (A) TO AVIRON OR ANY SUBSIDIARY THEREOF, (B) TO A QUALIFIED
INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (C)
TO AN INSTITUTIONAL ACCREDITED INVESTOR THAT, PRIOR TO SUCH TRANSFER, FURNISHES
TO MARINE MIDLAND BANK, AS TRUSTEE (OR A SUCCESSOR TRUSTEE, AS APPLICABLE), A
SIGNED LETTER CONTAINING CERTAIN REPRESENTATIONS AND AGREEMENTS RELATING TO THE
RESTRICTIONS ON TRANSFER OF THE NOTE EVIDENCED HEREBY (THE FORM OF WHICH LETTER
CAN BE OBTAINED FROM SUCH TRUSTEE OR A SUCCESSOR TRUSTEE, AS APPLICABLE), (D)
PURSUANT TO THE EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE
SECURITIES ACT (IF AVAILABLE) OR (E) PURSUANT TO A REGISTRATION STATEMENT WHICH
HAS BEEN DECLARED EFFECTIVE UNDER THE SECURITIES ACT (AND WHICH CONTINUES TO BE
EFFECTIVE AT THE TIME OF SUCH TRANSFER); (3) PRIOR TO SUCH TRANSFER (OTHER THAN
A TRANSFER PURSUANT TO CLAUSE 2(E) ABOVE), IT WILL FURNISH TO MARINE MIDLAND
BANK, AS TRUSTEE (OR A SUCCESSOR TRUSTEE, AS APPLICABLE), SUCH CERTIFICATIONS,
LEGAL OPINIONS OR OTHER INFORMATION AS IT MAY REASONABLY REQUIRE TO CONFIRM THAT
SUCH TRANSFER IS BEING MADE PURSUANT TO AN EXEMPTION FROM OR IN A TRANSACTION

                                      -1-
<PAGE>
 
NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND (4)
AGREES THAT IT WILL DELIVER TO EACH PERSON TO WHOM THE NOTE EVIDENCED HEREBY IS
TRANSFERRED A NOTICE SUBSTANTIALLY TO THE EFFECT OF THIS LEGEND.  IN CONNECTION
WITH ANY TRANSFER OF THE NOTE EVIDENCED HEREBY PRIOR TO THE EXPIRATION OF THE
HOLDING PERIOD APPLICABLE TO SALES OF THE NOTE EVIDENCED HEREBY UNDER RULE
144(K) UNDER THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION), THE HOLDER MUST
CHECK THE APPROPRIATE BOX SET FORTH ON THE REVERSE HEREOF RELATING TO THE MANNER
OF SUCH TRANSFER AND SUBMIT THIS CERTIFICATE TO MARINE MIDLAND BANK, AS TRUSTEE
(OR A SUCCESSOR TRUSTEE, AS APPLICABLE).  IF THE PROPOSED TRANSFEREE IS AN
INSTITUTIONAL ACCREDITED INVESTOR, THE HOLDER MUST, PRIOR TO SUCH TRANSFER,
FURNISH TO MARINE MIDLAND BANK, AS TRUSTEE (OR A SUCCESSOR TRUSTEE, AS
APPLICABLE), SUCH CERTIFICATIONS, LEGAL OPINIONS OR OTHER INFORMATION AS IT MAY
REASONABLY REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING MADE PURSUANT TO AN
EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION
REQUIREMENTS OF THE SECURITIES ACT.  THIS LEGEND WILL BE REMOVED UPON THE
EARLIER OF THE TRANSFER OF THE NOTE EVIDENCED HEREBY PURSUANT TO CLAUSE 2(E)
ABOVE OR UPON ANY TRANSFER OF THE NOTES EVIDENCED HEREBY UNDER RULE 144(K) UNDER
THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION).

                                      -2-
<PAGE>
 
                                     AVIRON

                 5 3/4% CONVERTIBLE SUBORDINATED NOTE DUE 2005

No:____                                                             CUSIP:______
                                                                $_______________

     AVIRON, a corporation duly organized and validly existing under the laws of
the State of Delaware (herein called the "Company", which term includes any
successor corporation under the Indenture referred to on the reverse hereof),
for value received hereby promises to pay to ____________________________ or
registered assigns, the principal sum of __________________ ($____________) on
April 1, 2005, at the office or agency of the Company maintained for that
purpose in accordance with the terms of the Indenture, or, at the option of the
holder of this Note, at the Corporate Trust Office, in such coin or currency of
the United States of America as at the time of payment shall be legal tender for
the payment of public and private debts, and to pay interest, semi-annually on
April 1 and October 1 of each year, commencing October 1, 1998, on said
principal sum at said office or agency, in like coin or currency, at the rate
per annum of 5 3/4%, from April 1 or October 1, as the case may be, next
preceding the date of this Note to which interest has been paid or duly provided
for, unless the date hereof is a date to which interest has been paid or duly
provided for, in which case from the date of this Note, or unless no interest
has been paid or duly provided for on the Notes, in which case from March 30,
1998, until payment of said principal sum has been made or duly provided for.
Notwithstanding the foregoing, if the date hereof is after any March 15 or
September 15, as the case may be, and before the following April 1 or October 1,
this Note shall bear interest from such April 1 or October 1; provided, however,
that if the Company shall default in the payment of interest due on such April 1
or October 1, then this Note shall bear interest from the next preceding April 1
or October 1, to which interest has been paid or duly provided for or, if no
interest has been paid or duly provided for on such Note, from March 30, 1998.
The interest payable on the Note pursuant to the Indenture on any April 1 or
October 1 will be paid to the Person entitled thereto as it appears in the Note
register at the close of business on the record date, which shall be the March
15 or September 15 (whether or not a Business Day) next preceding such April 1
or October 1, as provided in the Indenture; provided that any such interest not
punctually paid or duly provided for shall be payable as provided in the
Indenture.  Interest may, at the option of the Company, be paid either (i) by
check mailed to the registered address of such Person (provided that the holder
of Notes with an aggregate principal amount in excess of $2,000,000 shall, at
the written election of such holder, be paid by wire transfer in immediately
available funds) or (ii) by transfer to an account maintained by such Person
located in the United States; provided, however, that payments to the Depositary
will be made by wire transfer of immediately available funds to the account of
the Depositary or its nominee.

     Reference is made to the further provisions of this Note set forth on the
reverse hereof, including, without limitation, provisions subordinating the
payment of principal of and premium, if any, and interest on the Notes to the
prior payment in full of all Senior Indebtedness, as defined in the Indenture,
and provisions giving the holder of this Note the right to convert this Note
into Common Stock of the Company on the terms and subject to the limitations
referred to on the reverse hereof and as more fully

                                      -3-
<PAGE>
 
specified in the Indenture.  Such further provisions shall for all purposes have
the same effect as though fully set forth at this place.

     This Note shall be deemed to be a contract made under the laws of the State
of New York, and for all purposes shall be construed in accordance with and
governed by the laws of said State.

     This Note shall not be valid or become obligatory for any purpose until the
certificate of authentication hereon shall have been manually signed by the
Trustee or a duly authorized authenticating agent under the Indenture.


                                      -4-
<PAGE>
 
     IN WITNESS WHEREOF, the Company has caused this Note to be duly executed
under its corporate seal to be affixed or imported hereon.

                                    AVIRON


[seal]                        By:_____________________________________________
                              Name:
                              Title:


                            Attest:___________________________________________
                              Name:
                              Title:


Dated:  ____________________

TRUSTEE'S CERTIFICATE OF AUTHENTICATION

This is one of the Notes described in the within-named Indenture.

MARINE MIDLAND BANK, as Trustee


By:___________________________________
          Authorized Signatory


By:___________________________________
          As Authenticating Agent
          (if different from Trustee)


                                      -5-
<PAGE>
 
                           [FORM OF REVERSE OF NOTE]

                                    AVIRON

                 5 3/4% CONVERTIBLE SUBORDINATED NOTE DUE 2005


     This Note is one of a duly authorized issue of Notes of the Company,
designated as its 5 3/4% Convertible Subordinated Notes due 2005 (herein called
the "Notes"), limited to the aggregate principal amount of $115,000,000 all
issued or to be issued under and pursuant to an indenture dated as of March 15,
1998 (herein called the "Indenture"), between the Company and Marine Midland
Bank, as trustee (herein called the "Trustee"), to which Indenture and all
indentures supplemental thereto reference is hereby made for a description of
the rights, limitations of rights, obligations, duties and immunities thereunder
of the Trustee, the Company and the holders of the Notes.

     In case an Event of Default, as defined in the Indenture, shall have
occurred and be continuing, the principal of, premium, if any, and accrued
interest (including Liquidated Damages Amount, if any) on all Notes may be
declared, and upon said declaration shall become, due and payable, in the
manner, with the effect and subject to the conditions provided in the Indenture.

     The Indenture contains provisions permitting the Company and the Trustee,
with the consent of the holders of not less than a majority in aggregate
principal amount of the Notes at the time outstanding, evidenced as in the
Indenture provided, to execute supplemental indentures adding any provisions to
or changing in any manner or eliminating any of the provisions of the Indenture
or of any supplemental indenture or modifying in any manner the rights of the
holders of the Notes; provided, however, that no such supplemental indenture
shall (i) extend the fixed maturity of any Note, or reduce the rate or extend
the time of payment of interest thereon, or reduce the principal amount thereof
or premium, if any, thereon, or reduce any amount payable on redemption thereof,
or impair the right of any Noteholder to institute suit for the payment thereof,
or make the principal thereof or interest or premium, if any, thereon payable in
any coin or currency other than that provided in the Note, or modify the
provisions of the Indenture with respect to the subordination of the Notes in a
manner adverse to the Noteholders in any material respect, or change the
obligation of the Company to make redemption of any Note upon the happening of a
Fundamental Change in a manner adverse to the holder of the Notes, or impair the
right to convert the Notes into Common Stock subject to the terms set forth in
the Indenture, including Section 15.6 thereof, without the consent of the holder
of each Note so affected or (ii) reduce the aforesaid percentage of Notes, the
holders of which are required to consent to any such supplemental indenture,
without the consent of the holders of all Notes then outstanding. Subject to the
provisions of the Indenture, the holders of a majority in aggregate principal
amount of the Notes at the time outstanding may on behalf of the holders of all
of the Notes waive any past default or Event of Default under the Indenture and
its consequences except a default in the payment of interest (including
Liquidated Damages Amount, if any) or any premium on or the principal of any of
the Notes, a default in the payment of redemption price pursuant to Article III
or a failure by the Company to convert any Notes into Common Stock of the
Company or a default in respect of a covenant or provisions hereof which under
Article XI cannot be modified without the consent of the holders of each or all
Notes then

                                      -6-
<PAGE>
 
outstanding or affected thereby.  Any such consent or waiver by the holder of
this Note (unless revoked as provided in the Indenture) shall be conclusive and
binding upon such holder and upon all future holders and owners of this Note and
any Notes which may be issued in exchange or substitute hereof, irrespective of
whether or not any notation thereof is made upon this Note or such other Notes.

     The indebtedness evidenced by the Notes is, to the extent and in the manner
provided in the Indenture, expressly subordinate and subject in right of payment
to the prior payment in full of all Senior Indebtedness of the Company, as
defined in the Indenture, whether outstanding at the date of the Indenture or
thereafter incurred, and this Note is issued subject to the provisions of the
Indenture with respect to such subordination.  Each holder of this Note, by
accepting the same, agrees to and shall be bound by such provisions and
authorizes the Trustee on its behalf to take such action as may be necessary or
appropriate to effectuate the subordination so provided and appoints the Trustee
his attorney-in-fact for such purpose.

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

     Interest on the Notes shall be computed on the basis of a 360-day year of
twelve 30-day months.

     The Notes are issuable in registered form without coupons in denominations
of $1,000 and any integral multiple of $1,000.  At the office or agency of the
Company referred to on the face hereof, and in the manner and subject to the
limitations provided in the Indenture, without payment of any service charge but
with payment of a sum sufficient to cover any tax or other governmental charge
that may be imposed in connection with any registration or exchange of Notes,
Notes may be exchanged for a like aggregate principal amount of Notes of other
authorized denominations.

     The Notes will not be redeemable at the option of the Company prior to
April 6, 2001.  At any time on or after April 6, 2001, and prior to maturity,
the Notes may be redeemed at the option of the Company as a whole, or from time
to time in part, upon mailing a notice of such redemption not less than 30 days
before the date fixed for redemption to the holders of Notes at their last
registered addresses, all as provided in the Indenture, at the following
optional redemption prices (expressed as percentages of the principal amount),
together in each case with accrued interest (including Liquidated Damages
Amount, if any) to, but excluding, the date fixed for redemption:

     If redeemed during the period beginning April 6, 2001 and ending on March
31, 2002, at a redemption price of 103.286 and if redeemed during the 12-month
period beginning April 1:

<TABLE>
<CAPTION>
                   YEAR                         REDEMPTION PRICE
                   ----                         ----------------
                  <S>                             <C>
                   2002.........................    102.464%
                   2003.........................    101.643
                   2004.........................    100.821
</TABLE>


                                      -7-
<PAGE>
 
and 100% at April 1, 2005; provided that if the date fixed for redemption is on
April 1 or October 1, then the interest payable on such date shall be paid to
the holder of record on the next preceding March 15 or September 15,
respectively.

     The Company shall not give notice of any redemption if a default in the
payment of interest on the Notes has occurred and is continuing.

     The Notes are not subject to redemption through the operation of any
sinking fund.

     If a Fundamental Change (as defined in the Indenture) occurs at any time
prior to maturity of the Notes, the Notes will be redeemable on the 30th day
after notice thereof at the option of the holder at a redemption price equal to
100% of the principal amount thereof, together with accrued interest to (but
excluding) the date of redemption; provided that, if such Repurchase Date is
April 1 or October 1, the interest payable on such date shall be paid to the
holder of record of the Notes on the next preceding March 15 or September 15,
respectively.  The Company shall mail to all holders of record of the Notes a
notice of the occurrence of a Fundamental Change and of the redemption right
arising as a result thereof on or before the 10th day after the occurrence of
such Fundamental Change.  For a Note to be so repaid at the option of the
holder, the Company must receive at the office or agency of the Company
maintained for that purpose in accordance with the terms of the Indenture, such
Note with the form entitled "Option to Elect Repayment Upon a Fundamental
Change" on the reverse thereof duly completed, together with such Notes duly
endorsed for transfer, on or before the 30th day after the date of such notice
(or if such 30th day is not a Business Day, the immediately preceding Business
Day).

     Subject to the provisions of the Indenture, the holder hereof has the
right, at its option, at any time after 90 days following the original issuance
of any Notes through the close of business on the final maturity date of the
Notes, or, as to all or any portion hereof called for redemption, prior to the
close of business on the Business Day immediately preceding the date fixed for
redemption (unless the Company shall default in payment due upon redemption
thereof), to convert the principal hereof or any portion of such principal which
is $1,000 or an integral multiple thereof into that number of shares of the
Company's Common Stock, as said shares shall be constituted at the date of
conversion, obtained by dividing the principal amount of this Note or portion
thereof to be converted by the Conversion Price of $30.904 or such Conversion
Price as adjusted from time to time as provided in the Indenture, upon surrender
of this Note, together with a conversion notice as provided in the Indenture, to
the Company at the office or agency of the Company maintained for that purpose
in accordance with the terms of the Indenture, or at the option of such holder,
the Corporate Trust Office, and, unless the shares issuable on conversion are to
be issued in the same name as this Note, duly endorsed by, or accompanied by
instruments of transfer in form satisfactory to the Company duly executed by,
the holder or by his duly authorized attorney.  No adjustment in respect of
interest or dividends will be made upon any conversion; provided, however, that
if this Note shall be surrendered for conversion during the period from the
close of business on any record date for the payment of interest to the close of
business on the Business Day preceding the interest payment date, this Note
(unless it or the portion being converted shall have been called for redemption
during the period from the close of business on any record date for the payment
of interest to the close of business on the Business Day preceding the interest
payment date) must be accompanied by an amount, in New York Clearing House funds
or other funds acceptable

                                      -8-
<PAGE>
 
to the Company, equal to the interest payable on such interest payment date on
the principal amount being converted.  No fractional shares will be issued upon
any conversion, but an adjustment in cash will be made, as provided in the
Indenture, in respect of any fraction of a share which would otherwise be
issuable upon the surrender of any Note or Notes for conversion.

     Upon due presentment for registration of transfer of this Note at the
office or agency of the Company maintained for that purpose in accordance with
the terms of the Indenture, or at the option of the holder of this Note, at the
Corporate Trust Office, a new Note or Notes of authorized denominations for an
equal aggregate principal amount will be issued to the transferee in exchange
thereof; subject to the limitations provided in the Indenture, without charge
except for any tax or other governmental charge imposed in connection therewith.

     The Company, the Trustee, any authenticating agent, any paying agent, any
conversion agent and any Note registrar may deem and treat the registered holder
hereof as the absolute owner of this Note (whether or not this Note shall be
overdue and notwithstanding any notation of ownership or other writing hereon
made by anyone other than the Company or any Note registrar), for the purpose of
receiving payment hereof, or on account hereof, for the conversion hereof and
for all other purposes, and neither the Company nor the Trustee nor any other
authenticating agent nor any paying agent nor any other conversion agent nor any
Note registrar shall be affected by any notice to the contrary.  All payments
made to or upon the order of such registered holder shall, to the extent of the
sum or sums paid, satisfy and discharge liability for monies payable on this
Note.

     No recourse for the payment of the principal of or any premium or interest
on this Note, or for any claim based hereon or otherwise in respect hereof; and
no recourse under or upon any obligation, covenant or agreement of the Company
in the Indenture or any indenture supplemental thereto or in any Note, or
because of the creation of any indebtedness represented thereby, shall be had
against any incorporator, stockholder, employee, agent, officer or director or
subsidiary, as such, past, present or future, of the Company or of any successor
Person, either directly or through the Company or any successor Person, whether
by virtue of any constitution, statute or rule of law or by the enforcement of
any assessment or penalty or otherwise, all such liability being, by the
acceptance hereof and as part of the consideration for the issue hereof,
expressly waived and released.

     This Note shall be deemed to be a contract made under the laws of New York,
and for all purposes shall be construed in accordance with the laws of New York,
without regard to principles of conflicts of laws.

     Terms used in this Note and defined in the Indenture are used herein as
therein defined.


                                      -9-
<PAGE>
 
                                 ABBREVIATIONS


     The following abbreviations, when used in the inscription of the face of
this Note, shall be construed as though they were written out in full according
to applicable laws or regulations:

<TABLE>
<CAPTION>
<S>                                       <C>
TEN COM -  as tenants in common           UNIF GIFT MIN ACT -- ___________ Custodian ____________
TEN ENT -  as tenant by the entireties                            (Cust)                (Minor)
JT TEN -  as joint tenants with right     under Uniform Gifts to Minors Act
 of survivorship and not as
 tenants in common                        -------------------------------------------------------
                                                                  (State)

</TABLE> 
                   Additional abbreviations may also be used
                         though not in the above list.




                                     -10-
<PAGE>
 
                               CONVERSION NOTICE



TO:  AVIRON

     The undersigned registered owner of this Note hereby irrevocably exercises
the option to convert this Note, or the portion hereof (which is $1,000 or an
integral multiple thereof) below designated, into shares of Common Stock of
Aviron in accordance with the terms of the Indenture referred to in this Note,
and directs that the shares issuable and deliverable upon such conversion,
together with any check in payment for fractional shares and any Notes
representing any unconverted principal amount hereof, be issued and delivered to
the registered holder hereof unless a different name has been indicated below.
If shares or any portion of this Note not converted are to be issued in the name
of a person other than the undersigned, the undersigned will check the
appropriate box below and pay all transfer taxes payable with respect thereto.
Any amount required to be paid to the undersigned on account of interest
accompanies this Note.

Dated: ________________



                                    __________________________________________



                                    __________________________________________ 
                                    Signature(s)

                                    Signature(s) must be guaranteed by a
                                    commercial bank or trust company or a member
                                    firm of a major stock exchange if shares of
                                    Common Stock are to be issued, or Notes to
                                    be delivered, other than to and in the name
                                    of the registered holder.



                                    __________________________________________ 
                                    Signature Guarantee


                                     -11-
<PAGE>
 
Fill in for registration of shares of Common Stock if to be issued, and Notes if
to be delivered, other than to and in the name of the registered holder:



_____________________________________ 
(Name)


_____________________________________ 
(Street Address)


_____________________________________ 
(City, State and Zip Code)


Please print name and address


Principal amount to be converted
(if less than all):  $____________


Social Security or Other Taxpayer
Identification Number__________________



                                     -12-
<PAGE>
 
                           OPTION TO ELECT REPAYMENT
                           UPON A FUNDAMENTAL CHANGE



TO:  AVIRON

     The undersigned registered owner of this Note hereby irrevocably
acknowledges receipt of a notice from Aviron (the "Company") as to the
occurrence of a Fundamental Change with respect to the Company and requests and
instructs the Company to repay the entire principal amount of this Note, or the
portion thereof (which is $1,000 or an integral multiple thereof) below
designated, in accordance with the terms of the Indenture referred to in this
Note at the redemption price, together with accrued interest to, but excluding,
such date, to the registered holder hereof.

Dated:_________                 ________________________________________________


                                   _____________________________________________
                                   Signature(s)

                                   NOTICE: The above signatures of the holder(s)
                                   hereof must correspond with the name as
                                   written upon the face of the Note in every
                                   particular without alteration or enlargement
                                   or any change whatever.

                                   Principal amount to be converted (if less
                                   than all):

                                          $__________



                                    ____________________________________________
                                          Social Security or Other Taxpayer
                                                Identification Number
<PAGE>
 
                                  ASSIGNMENT


     For value received ______________________________ hereby sell(s), assign(s)
and transfer(s) unto ______________________________ (Please insert social
security or other Taxpayer Identification Number of assignee) the within Note,
and hereby irrevocably constitutes and appoints _________________________
attorney to transfer the said Note on the books of the Company, with full power
of substitution in the premises.

     In connection with any transfer of the Note within the period prior to the
expiration of the holding period applicable to sales thereof under Rule 144(k)
under the Securities Act (or any successor provision) (other than any transfer
pursuant to a registration statement that has been declared effective under the
Securities Act), the undersigned confirms that such Note is being transferred:

     [_]    To Aviron or a subsidiary thereof, or

     [_]    Pursuant to and in compliance with Rule 144A under the Securities
            Act of 1933, as amended; or

     [_]    To an Institutional Accredited Investor pursuant to and in
            compliance with the Securities Act of 1933, as amended, in a minimum
            denomination of $100,000; or

     [_]    Pursuant to and in compliance with Rule 144 under the Securities Act
            of 1933, as amended;

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

     [_]    The transferee is an Affiliate of the Company.

Dated:__________        ________________________________________________________


                              __________________________________________________
                              Signature(s)

                              Signature(s) must be guaranteed by a commercial
                              bank or trust company or a member firm of a major
                              stock exchange if shares of Common Stock are to be
                              issued, or Notes to be delivered, other than to or
                              in the name of the registered holder.
<PAGE>
 
                              __________________________________________________
                              Signature Guarantee

NOTICE:  The signature on the conversion notice, the option to elect repayment
upon a Fundamental Change or the assignment must correspond with the name as
written upon the face of the Note in every particular without alteration or
enlargement or any change whatever.
<PAGE>
 
                                   EXHIBIT B


Aviron
297 North Bernardo Avenue
Mountain View, CA  94043


Marine Midland Bank
140 Broadway, 12th Floor
New York, New York  10005


Ladies/Gentlemen:


     We are delivering this letter in connection with an offering of __%
Convertible Subordinated Notes due 2005 (the "Notes), which are convertible into
shares of Common  Stock, $.01 par value (the "Common Stock"), of Aviron (the
"Company").

     We hereby confirm that:

     .    we are an "accredited investor" within the meaning of Rule 501(a)(1),
          (2) or (3) under the Securities Act of 1933, as amended (the
          "Securities Act"), or an entity in which all of the equity owners are
          accredited investors within the meaning of Rule 501(a)(1), (2) or (3)
          under the Securities Act (an "Institutional Accredited Investor");

     .    any purchase of Notes by us will be for our own account or for
          the account of one or more other Institutional Accredited Investors or
          as fiduciary for the account of one or more trusts, each of which is
          an "accredited investor" within the meaning of Rule 501(a)(7) under
          the Securities Act and for each of which we exercise sole investment
          discretion or (B) we are a "bank," within the meaning of Section
          3(a)(2) of the Securities Act, or a "savings and loan association" or
          other institution described in Section 3(a)(5)(A) of the Securities
          Act that is acquiring Notes as fiduciary for the account of one or
          more institutions for which we exercise sole investment discretion;

     .    in the event that we purchase any Notes, we will acquire Notes having
          a minimum principal amount of not less than $100,000 for our own
          account or for any separate account for which we are acting;

     .    we have such knowledge and experience in financial and business
          matters that we are capable of evaluating the merits and risks of
          purchasing the Notes;
<PAGE>
 
     .    we are not acquiring Notes with a view to distribution thereof or with
          any present intention of offering or selling Notes or the Common Stock
          issuable upon conversion thereof, except as permitted below; provided
          that the disposition of our property and property of any accounts for
          which we are acting as fiduciary shall remain at all times within our
          control; and

     .    we have received a copy of the Offering Memorandum and acknowledge
          that we have had access to such financial and other information, and
          have been afforded the opportunity to ask such questions or
          representatives of the Company and receive answers thereto, as we deem
          necessary in connection with our decision to purchase Notes.


     We understand that the Notes are being offered in a transaction not
involving any public offering within the meaning of the Securities Act and that
the Notes and the Common Stock issuable upon conversion thereof have not been
registered under the Securities Act, and we agree, on our own behalf and on
behalf of each account for which we acquire any Notes, that if in the future we
decide to resell or otherwise transfer such Notes or the Common Stock issuable
upon conversion thereof, such Notes or Common Stock may be resold or otherwise
transferred only (i) to the Company or any subsidiary thereof, or (ii) to a
person who is a "qualified institutional buyer" (as defined in Rule 144A under
the Securities Act) in a transaction meeting the requirements of Rule 144A, or
(iii) to an Institutional Accredited Investor that, prior to such transfer,
furnishes to the Trustee for the Notes  (or in the case of the Common Stock, the
transfer agent therefor) a signed letter containing certain representations and
agreements relating to the restrictions on transfer of such securities (the form
of which letter can be obtained from the Trustee or transfer agent, as the case
may be), or (iv) pursuant to the exemption from registration provided by Rule
144 under the Securities Art (if applicable), or (v) pursuant to a registration
statement that has been declared effective under the Securities Act (and which
continues to be effective at the time of such transfer), and in each case, in
accordance with any applicable securities laws of any State of the United States
or any other applicable jurisdiction and in accordance with the legends set
forth on the Notes or the Common Stock issuable upon conversion thereof.  We
further agree to provide any person purchasing any of the Notes or the Common
Stock issuable upon conversion thereof other than pursuant to clause (v) above
from us a notice advising such purchaser that resales of such securities are
restricted as stated herein.  We understand that the Trustee or transfer agent
for the Notes and the Common Stock will not be required to accept for
registration of transfer any Notes or any Common Stock issued upon conversion of
the Notes except upon presentation of evidence satisfactory to the Company that
the foregoing restrictions on transfer have been complied with.  We further
understand that any Notes and any Common Stock issued upon conversion of the
Notes will be in the form of definitive physical certificates and that such
certificates will bear a legend reflecting the substance of this paragraph other
than pursuant to clause (v) above.

     We acknowledge that the Company, others and you will rely upon our
confirmations, acknowledgments and agreements set forth herein, and we agree to
notify you promptly in writing if any of our representations or warranties
herein ceases to be accurate and complete.
<PAGE>
 
     THIS LETTER SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE
INTERNAL LAWS OF THE STATE OF NEW YORK



                              _________________________________________________ 
                              (Name of Purchaser)



                              By:______________________________________________

                              Name:____________________________________________

                              Title:___________________________________________

                              Address:_________________________________________
 
                              _________________________________________________

                              _________________________________________________

<PAGE>
 
                                                                    EXHIBIT 4.13





                                 $100,000,000


                                    AVIRON
                                        
                5 3/4 % CONVERTIBLE SUBORDINATED NOTES DUE 2005



                              PURCHASE AGREEMENT



March 24, 1998
<PAGE>
 
                                 March 24, 1998


Morgan Stanley & Co. Incorporated
Bear Stearns & Co.
Credit Suisse First Boston Corporation
Hambrecht & Quist LLC
c/o Morgan Stanley & Co. Incorporated
    1585 Broadway
    New York, New York 10036

Dear Sirs and Mesdames:

     Aviron, a Delaware corporation (the "COMPANY"), proposes to issue and sell
to the several purchasers named in Schedule I hereto (the "INITIAL PURCHASERS")
$100,000,000 principal amount of its 5 3/4% Convertible Subordinated Notes due
2005 (the "FIRM SECURITIES") to be issued pursuant to the provisions of an
Indenture dated as of March 15, 1998 (the "INDENTURE") between the Company and
Marine Midland Bank, as Trustee (the "TRUSTEE").  The Company also proposes to
issue and sell to the Initial Purchasers not more than an additional $15,000,000
principal amount of its 5 3/4% Convertible Subordinated Notes due 2005 (the
"ADDITIONAL SECURITIES") if and to the extent that you, as Managers of the
offering, shall have determined to exercise, on behalf of the Initial
Purchasers, the right to purchase such 5 3/4% Convertible Subordinated Notes due
2005 granted to the Initial Purchasers in Section 2 hereof.  The Firm Securities
and the Additional Securities are hereinafter collectively referred to as the
"SECURITIES."  The Securities will be convertible into shares of common stock,
$0.001 par value, of the Company (the "UNDERLYING SECURITIES").

     The Securities and the Underlying Securities will be offered without being
registered under the Securities Act of 1933, as amended (the "SECURITIES ACT"),
to qualified institutional buyers in compliance with the exemption from
registration provided by Rule 144A under the Securities Act and to institutional
accredited investors (as defined in Rule 501(a)(1), (2), (3) or (7) under the
Securities Act) that deliver a letter in the form annexed to the Final
Memorandum (as defined below).

     The Initial Purchasers and their direct and indirect transferees will be
entitled to the benefits of a Registration Rights Agreement dated the date
hereof between the Company and the Initial Purchasers (the "REGISTRATION RIGHTS
AGREEMENT").

     In connection with the sale of the Securities, the Company has prepared a
preliminary offering memorandum (the "PRELIMINARY MEMORANDUM") and will prepare
a final offering memorandum (the "FINAL MEMORANDUM" and, with the Preliminary
Memorandum, each a "MEMORANDUM") including or incorporating by reference a
description of the terms of the Securities and the Underlying Securities, the
terms of the offering and a description of the Company.  As used herein, the
term "Memorandum" shall include in each case the documents incorporated by
reference therein.  The terms "SUPPLEMENT", "AMENDMENT" and "AMEND" as used
herein with respect to a
<PAGE>
 
Memorandum shall include all documents deemed to be incorporated by reference in
the Preliminary Memorandum or Final Memorandum that are filed subsequent to the
date of such Memorandum with the Securities and Exchange Commission (the
"COMMISSION") pursuant to the Securities Exchange Act of 1934, as amended (the
"EXCHANGE ACT").

     1.   Representations and Warranties.  The Company represents and warrants
to, and agrees with, you that:

          (a) (i) Each document, if any, filed or to be filed pursuant to the
Exchange Act and incorporated by reference in either Memorandum complied or will
comply when so filed in all material respects with the Exchange Act and the
applicable rules and regulations of the Commission thereunder and (ii) the
Preliminary Memorandum does not contain and the Final Memorandum, in the form
used by the Initial Purchasers to confirm sales and on the Closing Date (as
defined in Section 4), will not contain any untrue statement of a material fact
or omit to state a material fact necessary to make the statements therein, in
the light of the circumstances under which they were made, not misleading,
except that the representations and warranties set forth in this paragraph do
not apply to statements or omissions in either Memorandum based upon information
relating to any Initial Purchaser furnished to the Company in writing by such
Initial Purchaser through you expressly for use therein.

          (b) The Company has been duly incorporated, is validly existing as a
corporation in good standing under the laws of the jurisdiction of its
incorporation, has the corporate power and authority to own its property and to
conduct its business as described in each Memorandum and is duly qualified to
transact business and is in good standing in each jurisdiction in which the
conduct of its business or its ownership or leasing of property requires such
qualification, except to the extent that the failure to be so qualified or be in
good standing would not have a material adverse effect on the Company.

          (c)  The Company does not own or control, directly or indirectly, any
corporation, association or other entity.

          (d) The Company does not own any real properties. The Company has good
and marketable title to all personal property owned by it, in all such cases
free and clear of all liens, encumbrances and defects except such as are
described in the Final Memorandum or such as do not materially affect the value
of such property and do not interfere with the use made and proposed to be made
of such property by the Company, and any real property and buildings held under
lease by the Company are held by it under valid, subsisting and enforceable
leases except with such exceptions as are not material and do not interfere with
the current and proposed use of such property and buildings by the Company, in
all such cases except as described in or contemplated by the Final Memorandum.

          (e) This Agreement has been duly authorized, executed and delivered
by the Company.


                                       2
<PAGE>
 
          (f) The authorized capital stock of the Company conforms as to legal
matters to the description thereof contained in the Final Memorandum.

          (g) The shares of common stock outstanding on the date hereof have
been duly authorized and are validly issued, fully paid and non-assessable.

          (h) The Securities have been duly authorized and, when executed and
authenticated in accordance with the provisions of the Indenture and delivered
to and paid for by the Initial Purchasers in accordance with the terms of this
Agreement, will be valid and binding obligations of the Company, enforceable in
accordance with their terms, subject to applicable bankruptcy, insolvency or
similar laws affecting creditors' rights generally and general principles of
equity, and will be entitled to the benefits of the Indenture and the
Registration Rights Agreement.

          (i) The Underlying Securities reserved for issuance upon conversion of
the Securities have been duly authorized and reserved and, when issued upon
conversion of the Securities in accordance with the terms of the Securities,
will be validly issued, fully paid and non-assessable, and the issuance of the
Underlying Securities will not be subject to any preemptive or similar rights.

          (j) Each of the Indenture and the Registration Rights Agreement has
been duly authorized, executed and delivered by, and is a valid and binding
agreement of, the Company, enforceable in accordance with its terms, subject to
applicable bankruptcy, insolvency or similar laws affecting creditors' rights
generally and general principles of equity and except as rights to
indemnification and contribution under the Registration Rights Agreement may be
limited under applicable law.

          (k) The execution and delivery by the Company of, and the performance
by the Company of its obligations under, this Agreement, the Indenture, the
Registration Rights Agreement and the Securities will not contravene any
provision of applicable law or the certificate of incorporation or by-laws of
the Company or any contract, agreement, instrument, lease or license or other
instrument binding upon the Company, or any judgment, order or decree of any
governmental body, agency or court having jurisdiction over the Company, and no
consent, approval, authorization or order of, or qualification with, any
governmental body or agency is required for the performance by the Company of
its obligations under this Agreement, the Indenture the Registration Rights
Agreement or the Securities, except such as may be required by the securities or
Blue Sky laws of the various states in connection with the offer and sale of the
Securities and by Federal and state securities laws with respect to the
Company's obligations under the Registration Rights Agreement.

          (l) There has not occurred any material adverse change, or any
development involving a prospective material adverse change, in the condition,
financial or otherwise, or in the earnings, business or operations of the
Company, from that set forth in the Final Memorandum.

          (m) There are no legal or governmental proceedings pending or
threatened to which the Company is a party or to which any of the properties of
the Company is subject other than

                                       3
<PAGE>
 
proceedings accurately described in all material respects in each Memorandum and
proceedings that would not have a material adverse effect on the Company, or on
the power or ability of the Company to perform its obligations under this
Agreement, the Indenture the Registration Rights Agreement or the Securities or
to consummate the transactions contemplated by the Final Memorandum.

          (n) The Company (i) is in compliance with any and all applicable
foreign, federal, state and local laws and regulations relating to the
protection of human health and safety, the environment or hazardous or toxic
substances or wastes, pollutants or contaminants ("ENVIRONMENTAL LAWS"), (ii)
has received all permits, licenses or other approvals required of them under
applicable Environmental Laws to conduct their respective businesses and (iii)
is in compliance with all terms and conditions of any such permit, license or
approval, except where such noncompliance with Environmental Laws, failure to
receive required permits, licenses or other approvals or failure to comply with
the terms and conditions of such permits, licenses or approvals would not,
singly or in the aggregate, have a material adverse effect on the Company.

          (o) The Company is not, and after giving effect to the offering and
sale of the Securities and the application of the proceeds thereof as described
in the Final Memorandum, will not be an "investment company" as such term is
defined in the Investment Company Act of 1940, as amended.

          (p) Neither the Company nor any affiliate (as defined in Rule 501(b)
of Regulation D under the Securities Act, an "AFFILIATE") of the Company has
directly, or through any agent, (i) sold, offered for sale, solicited offers to
buy or otherwise negotiated in respect of, any security (as defined in the
Securities Act) which is or will be integrated with the sale of the Securities
in a manner that would require the registration under the Securities Act of the
Securities or (ii) engaged in any form of general solicitation or general
advertising in connection with the offering of the Securities, (as those terms
are used in Regulation D under the Securities Act) or in any manner involving a
public offering within the meaning of Section 4(2) of the Securities Act.

          (q) It is not necessary in connection with the offer, sale and
delivery of the Securities to the Initial Purchasers in the manner contemplated
by this Agreement to register the Securities under the Securities Act or to
qualify the Indenture under the Trust Indenture Act of 1939, as amended.

          (r) The Securities satisfy the requirements set forth in Rule
144A(d)(3) under the Securities Act.

          (s) The Company possesses all consents, approvals, orders,
certificates, authorizations and permits issued by, and have made all
declarations and filings with, all appropriate federal, state or foreign
governmental or self-regulatory authorities and all courts and other tribunals
necessary to conduct its business and to own, lease, license and use its
properties in the manner described in the Final Memorandum, except to the extent
that the failure to obtain or file would not have a material adverse effect, and
the Company has not received any notice of proceedings relating to the
revocation or modification of any such consent, approval, order, certificate,
authorization or

                                       4
<PAGE>
 
permit that, singly or in the aggregate, if the subject of any unfavorable
decision, ruling or finding, or failure to obtain or file, would have a material
adverse effect on the Company, except as described in the Final Memorandum.
 
          (t) The Company maintains systems of internal accounting controls
sufficient to provide reasonable assurance that (i) transactions are executed in
accordance with management's general or specific authorizations; (ii)
transactions are recorded as necessary to permit preparation of financial
statements in conformity with generally accepted accounting principles and to
maintain asset accountability; (iii) access to assets is permitted only in
accordance with management's general or specific authorization; and (iv) the
recorded assets are compared with the existing assets at reasonable intervals
and appropriate action is taken with respect to any differences.

          (u) The Company owns or possesses adequate licenses or other rights to
use all patents, copyrights, trademarks, service marks, trade names, technology
and know-how necessary to conduct its businesses in the manner described in the
Final Memorandum or could obtain such licenses or rights on terms that would not
have a material adverse effect on the Company and, except as disclosed in the
Memorandum, the Company has not received any notice of infringement or conflict
with asserted rights of others with respect to any patents, copyrights,
trademarks, service marks, trade names, technology or know-how which could
reasonably be expected to result in any material adverse effect; and, except as
disclosed in the Final Memorandum, the discoveries, inventions, products or
processes of the Company referred to in the Final Memorandum do not, to the best
knowledge of the Company, infringe or conflict with any patent or other
intellectual property right of any third party, or any discovery, invention,
product or process that is the object of a patent application filed by any third
party known to the Company, except for any such infringement or conflict which
would not have a material adverse effect on the Company.

          (v) Since December 31, 1997, (i) the Company has not incurred any
material liability or obligation, direct or contingent, nor entered into any
material transaction not in the ordinary course of business; (ii) the Company
has not purchased any of its outstanding capital stock, nor declared, paid or
otherwise made any dividend or distribution of any kind on its capital stock
other than ordinary and customary dividends (other than the repurchase of
530,831 shares of common stock from Sang-A Pharm. Co., Inc. described in the
Final Memorandum); and (iii) there has not been any material change in the
capital stock, short-term debt or long-term debt of the Company, except in each
case as described in or contemplated by the Final Memorandum.

          (w) Neither the Company, nor to the Company's knowledge, any other
party thereto, is in violation or breach of, or in default with respect to, any
provision of any contract, agreement, instrument, lease or license to which the
Company is a party, in any respect that could have a material adverse effect on
the Company, and each such contract, agreement, instrument, lease or license is
in full force and effect and is the legal, valid and binding obligation of the
Company, and, to the Company's knowledge, other principal parties thereto. The
Company enjoys peaceful and undisturbed possession under all leases and licenses
under which they operate except as would

                                       5
<PAGE>
 
not have a material adverse effect on the Company.  The Company is not in
violation or breach of, or in default with respect to, any term of its
certificate of incorporation or bylaws.

          (x) The Company has timely filed all necessary federal, state and
foreign income and franchise tax returns and have paid all taxes shown thereon
as due (except for any failure to so file or so pay which would not have a
material adverse effect on the Company), and there is no tax deficiency that has
been or, to the Company's knowledge, might be asserted against the Company that
would have a material adverse effect on the Company; and all tax liabilities are
adequately provided for on the books of the Company.

          (y) Since the date of the Preliminary Memorandum, to the Company's
knowledge after due inquiry, no executive officer or director of the Company has
sold, contracted to sell or otherwise transferred or agreed to transfer the
economic consequences or ownership of any shares of common stock of the Company
or any securities convertible into or exchangeable or exercisable for or any
rights to purchase or acquire common stock of the Company.

          (z) No labor dispute with employees of the Company exists or, to the
knowledge of the Company, is imminent that could result in a material adverse
effect on the Company, and the Company is not aware of any existing, threatened
or imminent labor disturbance by the employees of any of its principal
suppliers, manufacturers or contractors that could result in any material
adverse effect on the Company.

          (aa) The Company is insured by insurers of recognized financial
responsibility against such losses and risks and in such amounts as are prudent
and customary in the businesses in which they are engaged; the Company has not
been refused any insurance coverage sought or applied for; and the Company does
not have any reason to believe that it will not be able to renew its existing
insurance coverage as and when such coverage expires or to obtain similar
coverage from similar insurers as may be necessary to continue its business at a
cost that would not have an material adverse effect on the Company, except as
described in or contemplated by the Final Memorandum.

          (bb) Ernst & Young LLP, which has examined the financial statements of
the Company, together with the related schedules and notes, as of December 31,
1997, 1996 and 1995 and for each of the years in the three (3) years ended
December 31, 1997, which are included in the Final Memorandum, are independent
accountants within the meaning of the Act and the Rules and Regulations; the
audited financial statements of the Company, together with the related schedules
and notes forming part of the Final Memorandum, fairly present the financial
position and the results of operations of the Company at the respective dates
and for the respective periods to which they apply; and all audited financial
statements of the Company, together with the related schedules and notes
included as part of the Final Memorandum, have been prepared in accordance with
generally accepted accounting principles consistently applied throughout the
periods involved except as may be otherwise stated therein. The selected and
summary financial and statistical data included in the Final Memorandum present
fairly the information shown therein and have been compiled on a basis

                                       6
<PAGE>
 
consistent with the audited financial statements presented therein.  No other
financial statements or schedules are required to be included in the Final
Memorandum.

          (cc) The Company has not distributed and will not distribute prior to
the later of (i) the Closing Date, or the Option Closing Date, as the case may
be, and (ii) completion of the distribution of the Securities, any offering
material in connection with the offering and sale of the Securities other than
any Memorandum and other materials, if any, permitted by the Act.

          (dd) The Company has not at any time during the last five (5) years
(i) made any unlawful contribution to any candidate for foreign office or failed
to disclose fully any contribution in violation of law, or (ii) made any payment
to any federal or state governmental officer or official, or other person
charged with similar public or quasi-public duties, other than payments required
or permitted by the laws of the United States or any jurisdiction thereof.

          (ee) The Company has not taken and will not take, directly or
indirectly, any action designed to or that might reasonably be expected to cause
or result in stabilization or manipulation of the price of the Securities or the
Underlying Securities to facilitate the sale or resale of the Securities.

     2.   Agreements to Sell and Purchase.  The Company hereby agrees to sell to
the several Initial Purchasers, and each Initial Purchaser, upon the basis of
the representations and warranties herein contained, but subject to the
conditions hereinafter stated, agrees, severally and not jointly, to purchase
from the Company the respective principal amount of Firm Securities set forth in
Schedule I hereto opposite its name at a purchase price of 96.5% of the
principal amount thereof (the "PURCHASE PRICE").

     On the basis of the representations and warranties contained in this
Agreement, and subject to its terms and conditions, the Company agrees to sell
to the Initial Purchasers the Additional Securities, and the Initial Purchasers
shall have a one-time right to purchase, severally and not jointly, up to
$15,000,000 principal amount of Additional Securities at the Purchase Price plus
accrued interest, if any, to the date of payment and delivery.  If you, on
behalf of the Initial Purchasers, elect to exercise such option, you shall so
notify the Company in writing not later than 30 days after the date of this
Agreement, which notice shall specify the principal amount of Additional
Securities to be purchased by the Initial Purchasers and the date on which such
Additional Securities are to be purchased.  Such date may be the same as the
Closing Date but not earlier than the Closing Date nor later than ten business
days after the date of such notice.  Additional Securities may be purchased as
provided in Section 4 solely for the purpose of covering over-allotments made in
connection with the offering of the Firm Securities.  If any Additional
Securities are to be purchased, each Initial Purchaser agrees, severally and not
jointly, to purchase the principal amount of Additional Securities (subject to
such adjustments to eliminate fractional Securities as you may determine) that
bears the same proportion to the total principal amount of Additional Securities
to be purchased as the principal amount of Firm Securities set forth Schedule I
opposite the name of such Initial Purchaser bears to the total principal amount
of Firm Securities.

                                       7
<PAGE>
 
     The Company hereby agrees that, without the prior written consent of Morgan
Stanley & Co. Incorporated on behalf of the Initial Purchasers, it will not,
during the period ending 180 days after the date of the Final Memorandum, (i)
offer, pledge, sell, contract to sell, sell any option or contract to purchase,
purchase any option or contract to sell, grant any option, right or warrant to
purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any
shares of common stock or any securities convertible into or exercisable or
exchangeable for common stock or (ii) enter into any swap or other arrangement
that transfers to another, in whole or in part, any of the economic consequences
of ownership of the common stock, whether any such transaction described in
clause (i) or (ii) above is to be settled by delivery of common stock or such
other securities, in cash or otherwise.  The foregoing sentence shall not apply
to (A) the sale of the Securities under this Agreement, (B) the issuance by the
Company of any shares of common stock upon the exercise of an option or warrant
or the conversion of a security outstanding on the date hereof of which the
Initial Purchasers have been advised in writing or (C) the issuance by the
Company of any shares of common stock or options to purchase common stock under
the 1996 Equity Incentive Plan, the Nonemployee Directors' Plan or the Employee
Stock Purchase Plan.

     3.   Terms of Offering.  You have advised the Company that the Initial
Purchasers will make an offering of the Securities purchased by the Initial
Purchasers hereunder on the terms to be set forth in the Final Memorandum, as
soon as practicable after this Agreement is entered into as in your judgment is
advisable.

     4.   Payment and Delivery.  Payment for the Firm Securities shall be made
to the Company in Federal or other funds immediately available in New York City
against delivery of such Firm Securities for the respective accounts of the
several Initial Purchasers at 10:00 a.m., New York City time, on March 30, 1998,
or at such other time on the same or such other date, not later than March 30,
1998, as shall be designated in writing by you.  The time and date of such
payment are hereinafter referred to as the "CLOSING DATE."

     Payment for any Additional Securities shall be made to the Company in
Federal or other funds immediately available in New York City against delivery
of such Additional Securities for the respective accounts of the several Initial
Purchasers at 10:00 a.m., New York City time, on the date specified in the
notice described in Section 2 or at such other time on the same or on such other
date, in any event not later than April 30, 1998, as shall be designated in
writing by you.  The time and date of such payment are hereinafter referred to
as the "OPTION CLOSING DATE."

     Certificates for the Firm Securities and Additional Securities shall be in
definitive form or global form, as specified by you, and registered in such
names and in such denominations as you shall request in writing not later than
one full business day prior to the Closing Date or the Option Closing Date, as
the case may be.  The certificates evidencing the Firm Securities and Additional
Securities shall be delivered to you on the Closing Date or the Option Closing
Date, as the case may be, for the respective accounts of the several Initial
Purchasers, with any transfer taxes payable in connection with the transfer of
the Securities to the Initial Purchasers duly paid, against payment of the
Purchase Price therefor plus accrued interest, if any, to the date of payment
and delivery.

                                       8
<PAGE>
 
    5.    Conditions to the Initial Purchasers' Obligations.  The several
obligations of the Initial Purchasers to purchase and pay for the Firm
Securities on the Closing Date are subject to the following conditions:

          (a) Subsequent to the execution and delivery of this Agreement and
prior to the Closing Date:

              (i) there shall not have occurred any downgrading, nor shall any
notice have been given of any intended or potential downgrading or of any review
for a possible change that does not indicate the direction of the possible
change, in the rating accorded any of the Company's securities or in the rating
outlook for the Company by any "nationally recognized statistical rating
organization," as such term is defined for purposes of Rule 436(g)(2) under the
Securities Act.

              (ii) there shall not have occurred any change, or any development
involving a prospective change, in the condition, financial or otherwise, or in
the earnings, business or operations of the Company from that set forth in the
Final Memorandum (exclusive of any amendments or supplements thereto subsequent
to the date of this Agreement) that, in your judgment, is material and adverse
and that makes it, in your judgment, impracticable to market the Securities on
the terms and in the manner contemplated in the Final Memorandum.

          (b) The Initial Purchasers shall have received on the Closing Date a
certificate, dated the Closing Date and signed by an executive officer of the
Company, to the effect set forth in Section 5(a)(i) and to the effect that the
representations and warranties of the Company contained in this Agreement are
true and correct as of the Closing Date and that the Company has complied with
all of the agreements and satisfied all of the conditions on its part to be
performed or satisfied hereunder on or before the Closing Date.

              The officer signing and delivering such certificate may rely upon
the best of his or her knowledge as to proceedings threatened.

          (c) The Initial Purchasers shall have received on the Closing Date an
opinion of Cooley Godward LLP, outside counsel for the Company, dated the
Closing Date, to the effect set forth in Exhibit A.  Such opinion shall be
rendered to the Initial Purchasers at the request of the Company and shall so
state therein.

          (d) The Initial Purchasers shall have received on the Closing Date an
opinion of Pennie and Edmonds, patent counsel for the Company as to Section A of
the Patent portfolio, dated the Closing Date to the effect set forth in Exhibit
B.  Such opinion shall be rendered to the Initial Purchasers at the request of
the Company and shall so state therein.

          (e) The Initial Purchasers shall have received on the Closing Date an
opinion of Marshall O'Toole Gerstein Murray & Borun, patent counsel for the
Company as to Section B of the Patent folio, dated the Closing Date to the
effect set forth in Exhibit C.  Such opinion shall be rendered to the Initial
Purchasers at the request of the Company and shall so state therein.

                                       9
<PAGE>
 
          (f) The Initial Purchasers shall have received on the Closing Date an
opinion of Wilson Sonsini Goodrich & Rosati, Professional Corporation, counsel
for the Initial Purchasers, dated the Closing Date, to the effect set forth in
Exhibit D.

          (g) The Initial Purchasers shall have received on each of the date
hereof and the Closing Date a letter, dated the date hereof or the Closing Date,
as the case may be, in form and substance satisfactory to the Initial
Purchasers, from Ernst & Young LLP, independent public accountants, containing
statements and information of the type ordinarily included in accountants
"comfort letters" to underwriters with respect to the financial statements and
certain financial information contained in or incorporated by reference into
each Memorandum; provided that the letter delivered on the Closing Date shall
use a "cut-off date" not earlier than the date hereof.

          (h) The Lock-up Agreements (as defined below) of each officer and
director of the Company, a certain beneficial owner of an aggregate of 530,831
shares of the Company's outstanding shares of capital stock as of the date of
this Agreement ("Sang-A") and a certain beneficial owner of an aggregate of
2,655,280 shares of the Company's outstanding shares of capital stock as of the
date of this Agreement shall be in full force and effect as of the Closing Date
such that, without the prior written consent of Morgan Stanley & Co.
Incorporated on behalf of the Initial Purchasers, it will not, during the period
commencing on the date hereof and ending 90 days after the date of the Final
Memorandum, (1) offer, pledge, sell, contract to sell, sell any option or
contract to purchase, purchase any option or contract to sell, grant any option,
right or warrant to purchase, lend, or otherwise transfer or dispose of,
directly or indirectly, any shares of common stock or any securities convertible
into or exercisable or exchangeable for common stock or (2) enter into any swap
or other arrangement that transfers to another, in whole or in part, any of the
economic consequences of ownership of the common stock, whether any such
transaction described in clause (1) or (2) above is to be settled by delivery of
common stock or such other securities, in cash or otherwise. The foregoing
sentence shall not apply to transactions relating to shares of common stock or
other securities acquired in open market transactions after the completion of
the Offering. In addition, the Lock-up Agreements shall also provide that,
without the prior written consent of Morgan Stanley & Co. Incorporated on behalf
of the Initial Purchasers, each such officer, director and beneficial owner will
not, during the period commencing on the date hereof and ending 90 days after
the date of the Final Memorandum, make any demand for or exercise any right with
respect to, the registration of any shares of common stock or any security
convertible into or exercisable or exchangeable for common stock. With respect
to the Lock-up Agreement with Sang-A, such Lock-up Agreement shall terminate
upon the later to occur of (i) March 31, 1998, and (ii) the Closing Date. The
Company has provided to counsel for the Underwriters a complete and accurate
list of all securityholders of the Company and the number and type of securities
held by each securityholder. The Company has provided to counsel for the
Underwriters true, accurate and complete copies of all of the agreements
pursuant to which its officers, directors and stockholders have agreed to such
or similar restrictions (the "Lock-up Agreements") presently in effect or
effected hereby.

          (i) The Initial Purchasers shall have received on the Closing Date an
opinion of Reed Smith Shaw and McClay LLP, special New York counsel for the
Company, dated the Closing

                                      10
<PAGE>
 
Date, to the effect set forth in Exhibit E.  Such opinion shall be rendered to
the Initial Purchasers at the request of the Company and shall so state therein.

     The Company shall have furnished to you such further certificates and
documents as you shall reasonably request (including certificates on behalf of
the Company by officers of the Company), as to the accuracy of the
representations and warranties of the Company herein, as to the performance by
the Company of its obligations hereunder and as to the other conditions
concurrent and precedent to the obligations of the Initial Purchasers hereunder.

     The several obligations of the Initial Purchasers to purchase Additional
Securities hereunder are subject to the delivery to you on the Option Closing
Date of such documents as you may reasonably request with respect to the good
standing of the Company, the due authorization, execution and authentication and
issuance of the Additional Securities and other matters related to the execution
and authentication and issuance of the Additional Securities.

     6.   Covenants of the Company.  In further consideration of the agreements
of the Initial Purchasers contained in this Agreement, the Company covenants
with each Initial Purchaser as follows:

          (a) To furnish to you in New York City, without charge, prior to 10:00
a.m. New York City time on the business day next succeeding the date of this
Agreement and during the period mentioned in Section 6(c), as many copies of the
Final Memorandum, any documents incorporated by reference therein and any
supplements and amendments thereto as you may reasonably request.

          (b) Before amending or supplementing either Memorandum, to furnish to
you a copy of each such proposed amendment or supplement and not to use any such
proposed amendment or supplement to which you reasonably object.

          (c) If, during such period after the date hereof and prior to the date
on which all of the Securities shall have been sold by the Initial Purchasers,
any event shall occur or condition exist as a result of which it is necessary to
amend or supplement the Final Memorandum in order to make the statements
therein, in the light of the circumstances when the Final Memorandum is
delivered to a purchaser, not misleading, or if, in the opinion of counsel for
the Initial Purchasers, it is necessary to amend or supplement the Final
Memorandum to comply with applicable law, forthwith to prepare and furnish, at
its own expense, to the Initial Purchasers, either amendments or supplements to
the Final Memorandum so that the statements in the Final Memorandum as so
amended or supplemented will not, in the light of the circumstances when the
Final Memorandum is delivered to a purchaser, be misleading or so that the Final
Memorandum, as amended or supplemented, will comply with applicable law.

          (d) To endeavor to qualify the Securities for offer and sale under the
securities or Blue Sky laws of such jurisdictions as you shall reasonably
request.

                                      11
<PAGE>
 
          (e) Whether or not the transactions contemplated in this Agreement are
consummated or this Agreement is terminated, to pay or cause to be paid all
expenses incident to the performance of its obligations under this Agreement,
including:  (i) the fees, disbursements and expenses of the Company's counsel
and the Company's accountants in connection with the issuance and sale of the
Securities and all other fees or expenses in connection with the preparation of
each Memorandum and all amendments and supplements thereto, including all
printing costs associated therewith, and the delivering of copies thereof to the
Initial Purchasers, in the quantities herein above specified, (ii) all costs and
expenses related to the transfer and delivery of the Securities to the Initial
Purchasers, including any transfer or other taxes payable thereon, (iii) the
cost of printing or producing any Blue Sky or legal investment memorandum in
connection with the offer and sale of the Securities under state securities laws
and all expenses in connection with the qualification of the Securities for
offer and sale under state securities laws as provided in Section 6(d) hereof,
including filing fees and the reasonable fees and disbursements of counsel for
the Initial Purchasers in connection with such qualification and in connection
with the Blue Sky or legal investment memorandum, (iv) any fees charged by
rating agencies for the rating of the Securities, (v) all document production
charges and expenses of counsel to the Initial Purchasers (but not including
their fees for professional services) in connection with the preparation of this
Agreement, (vi) the fees and expenses, if any, incurred in connection with the
admission of the Securities for trading in Portal or any appropriate market
system, (vii) the costs and charges of the Trustee and any transfer agent,
registrar or depositary, (viii) the cost of the preparation, issuance and
delivery of the Securities, (ix) the costs and expenses of the Company relating
to investor presentations on any "road show" undertaken in connection with the
marketing of the offering of the Securities, including, without limitation,
expenses associated with the production of road show slides and graphics, fees
and expenses of any consultants engaged in connection with the road show
presentations with the prior approval of the Company, travel and lodging
expenses of the representatives and officers of the Company and any such
consultants, and the cost of any aircraft chartered in connection with the road
show, and (x) all other cost and expenses incident to the performance of the
obligations of the Company hereunder for which provision is not otherwise made
in this Section.  It is understood, however, that except as provided in this
Section, Section 8, and the last paragraph of Section 10, the Initial Purchasers
will pay all of their costs and expenses, including fees and disbursements of
their counsel, transfer taxes payable on resale of any of the Securities by them
and any advertising expenses connected with any offers they may make.

          (f) Neither the Company nor any Affiliate will sell, offer for sale or
solicit offers to buy or otherwise negotiate in respect of any security (as
defined in the Securities Act) which could be integrated with the sale of the
Securities in a manner which would require the registration under the Securities
Act of the Securities.

          (g) Not to solicit any offer to buy or offer or sell the Securities or
the Underlying Securities by means of any form of general solicitation or
general advertising (as those terms are used in Regulation D under the
Securities Act) or in any manner involving a public offering within the meaning
of Section 4(2) of the Securities Act.

                                      12
<PAGE>
 
          (h) While any of the Securities or the Underlying Securities remain
"restricted securities" within the meaning of the Securities Act, to make
available, upon request, to any seller of such Securities the information
specified in Rule 144A(d)(4) under the Securities Act, unless the Company is
then subject to Section 13 or 15(d) of the Exchange Act.

          (i) If requested by you, to use its best efforts to permit the
Securities to be designated Portal securities in accordance with the rules and
regulations adopted by the National Association of Securities Dealers, Inc.
relating to trading in The Portal Market.

          (j) During the period of two years after the Closing Date or the
Option Closing Date, if later, the Company will not, and will not permit any of
its affiliates (as defined in Rule 144A under the Securities Act) to resell any
of the Securities or the Underlying Securities which constitute "restricted
securities" under Rule 144A that have been reacquired by any of them.

          (k) The Company will not release any of its officers, directors or
other stockholders from any Lock-up Agreements currently existing or hereafter
effected without the prior written consent of Morgan Stanley & Co. Incorporated.

     7.   Offering of Securities; Restrictions on Transfer.

          (a) Each Initial Purchaser, severally and not jointly, represents and
warrants that such Initial Purchaser is a qualified institutional buyer as
defined in Rule 144A under the Securities Act (a "QIB").  Each Initial
Purchaser, severally and not jointly, agrees with the Company that (i) it will
not solicit offers for, or offer or sell, such Securities by any form of general
solicitation or general advertising (as those terms are used in Regulation D
under the Securities Act) or in any manner involving a public offering within
the meaning of Section 4(2) of the Securities Act and (ii) it will solicit
offers for such Securities only from, and will offer such Securities only to,
persons that it reasonably believes to be, (1) QIBs or (2) other institutional
accredited investors (as defined in Rule 501(a)(1), (2), (3) or (7) under the
Securities Act ("INSTITUTIONAL ACCREDITED INVESTORS")) that, prior to their
purchase of the Securities, deliver to such Initial Purchaser a letter
containing the representations and agreements set forth in Appendix A to the
Memorandum that, in each case, in purchasing such Securities are deemed to have
represented and agreed as provided in the Memorandum under the caption "Transfer
Restrictions".

          (b) Each Initial Purchaser, severally and not jointly, represents,
warrants, and agrees that:

              (i) such Initial Purchaser understands that no action has been or
will be taken in any jurisdiction by the Company that would permit a public
offering of the Securities, or possession or distribution of either Memorandum
or any other offering or publicity material relating to the Securities, in any
country or jurisdiction where action for that purpose is required;

                                      13
<PAGE>
 
              (ii) such Initial Purchaser will comply with all applicable laws
and regulations in each jurisdiction in which it acquires, offers, sells or
delivers Securities or has in its possession or distributes either Memorandum or
any such other material, in all cases at its own expense;

              (iii) the Securities have not been registered under the Securities
Act and may not be offered or sold except in accordance with Rule 144A under the
Securities Act or pursuant to another exemption from the registration
requirements of the Securities Act;

              (iv) such Initial Purchaser has (A) not offered or sold and, prior
to the date six months after the Closing Date, will not offer or sell any
Securities to persons in the United Kingdom except to persons whose ordinary
activities involve them in acquiring, holding, managing or disposing of
investments (as principal or agent) for the purposes of their businesses or
otherwise in circumstances which have not resulted and will not result in an
offer to the public in the United Kingdom within the meaning of the Public
Offers of Securities Regulations 1995; (B) complied and will comply with all
applicable provisions of the Financial Services Act 1986 with respect to
anything done by it in relation to the Securities in, from or otherwise
involving the United Kingdom, and (C) only issued or passed on and will only
issue or pass on in the United Kingdom any document received by it in connection
with the issue of the Securities to a person who is of a kind described in
Article II(3) of the Financial Services Act 1986 (Investment Advertisements)
(Exemptions) Order 1996 or is a person to whom such document may otherwise
lawfully be issued or passed on; and

              (v) such Initial Purchaser understands that the Securities have
not been and will not be registered under the Securities and Exchange Law of
Japan, and represents that it has not offered or sold, and agrees not to offer
or sell, directly or indirectly, any Securities in Japan or for the account of
any resident thereof except pursuant to any exemption from the registration
requirements of the Securities and Exchange Law of Japan and otherwise in
compliance with applicable provisions of Japanese law.


     8.   Indemnity and Contribution.

          (a) The Company agrees to indemnify and hold harmless each Initial
Purchaser and each person, if any, who controls any Initial Purchaser within the
meaning of either Section 15 of the Securities Act or Section 20 of the Exchange
Act from and against any and all losses, claims, damages and liabilities
(including, without limitation, any legal or other expenses reasonably incurred
in connection with defending or investigating any such action or claim) caused
by any untrue statement or alleged untrue statement of a material fact contained
in either Memorandum (as amended or supplemented if the Company shall have
furnished any amendments or supplements thereto), or caused by any omission or
alleged omission to state therein a material fact necessary to make the
statements therein in the light of the circumstances under which they were made
not misleading, except insofar as such losses, claims, damages or liabilities
are caused by any such untrue statement or omission or alleged untrue statement
or omission based upon information

                                      14
<PAGE>
 
relating to any Initial Purchaser furnished to the Company in writing by such
Initial Purchaser through you expressly for use therein.

          (b) Each Initial Purchaser agrees, severally and not jointly, to
indemnify and hold harmless the Company, its directors, its officers and each
person, if any, who controls the Company within the meaning of either Section 15
of the Securities Act or Section 20 of the Exchange Act to the same extent as
the foregoing indemnity from the Company to such Initial Purchaser, but only
with reference to information relating to such Initial Purchaser furnished to
the Company in writing by such Initial Purchaser through you expressly for use
in either Memorandum or any amendments or supplements thereto.

          (c) In case any proceeding (including any governmental investigation)
shall be instituted involving any person in respect of which indemnity may be
sought pursuant to Section 8(a) or 8(b), such person (the "INDEMNIFIED PARTY")
shall promptly notify the person against whom such indemnity may be sought (the
"INDEMNIFYING PARTY") in writing and the indemnifying party, upon request of the
indemnified party, shall retain counsel reasonably satisfactory to the
indemnified party to represent the indemnified party and any others the
indemnifying party may designate in such proceeding and shall pay the fees and
disbursements of such counsel related to such proceeding.  In any such
proceeding, any indemnified party shall have the right to retain its own
counsel, but the fees and expenses of such counsel shall be at the expense of
such indemnified party unless (i) the indemnifying party and the indemnified
party shall have mutually agreed to the retention of such counsel or (ii) the
named parties to any such proceeding (including any impleaded parties) include
both the indemnifying party and the indemnified party and representation of both
parties by the same counsel would be inappropriate due to actual or potential
differing interests between them. It is understood that the indemnifying party
shall not, in respect of the legal expenses of any indemnified party in
connection with any proceeding or related proceedings in the same jurisdiction,
be liable for the fees and expenses of more than one separate firm (in addition
to any local counsel) for all such indemnified parties and that all such fees
and expenses shall be reimbursed as they are incurred.  Such firm shall be
designated in writing by Morgan Stanley & Co. Incorporated, in the case of
parties indemnified pursuant to Section 8(a), and by the Company, in the case of
parties indemnified pursuant to Section 8(b).  The indemnifying party shall not
be liable for any settlement of any proceeding effected without its written
consent, but if settled with such consent or if there be a final judgment for
the plaintiff, the indemnifying party agrees to indemnify the indemnified party
from and against any loss or liability by reason of such settlement or judgment.
Notwithstanding the foregoing sentence, if at any time an indemnified party
shall have requested an indemnifying party to reimburse the indemnified party
for fees and expenses of counsel as contemplated by the second and third
sentences of this paragraph, the indemnifying party agrees that it shall be
liable for any settlement of any proceeding effected without its written consent
if (i) such settlement is entered into more than 30 days after receipt by such
indemnifying party of the aforesaid request and (ii) such indemnifying party
shall not have reimbursed the indemnified party in accordance with such request
prior to the date of such settlement.  No indemnifying party shall, without the
prior written consent of the indemnified party, effect any settlement of any
pending or threatened proceeding in respect of which any indemnified party is or
could have been a party and indemnity could have been sought

                                      15
<PAGE>
 
hereunder by such indemnified party, unless such settlement includes an
unconditional release of such indemnified party from all liability on claims
that are the subject matter of such proceeding.

          (d) To the extent the indemnification provided for in Section 8(a) or
8(b) is unavailable to an indemnified party or insufficient in respect of any
losses, claims, damages or liabilities referred to therein, then each
indemnifying party under such paragraph, in lieu of indemnifying such
indemnified party thereunder, shall contribute to the amount paid or payable by
such indemnified party as a result of such losses, claims, damages or
liabilities (i) in such proportion as is appropriate to reflect the relative
benefits received by the Company on the one hand and the Initial Purchasers on
the other hand from the offering of the Securities or (ii) if the allocation
provided by clause 8(d)(i) above is not permitted by applicable law, in such
proportion as is appropriate to reflect not only the relative benefits referred
to in clause 8(d)(i) above but also the relative fault of the Company on the one
hand and of the Initial Purchasers on the other hand in connection with the
statements or omissions that resulted in such losses, claims, damages or
liabilities, as well as any other relevant equitable considerations. The
relative benefits received by the Company on the one hand and the Initial
Purchasers on the other hand in connection with the offering of the Securities
shall be deemed to be in the same respective proportions as the net proceeds
from the offering of the Securities (before deducting expenses) received by the
Company and the total discounts and commissions received by the Initial
Purchasers, in each case as set forth in the Final Memorandum, bear to the
aggregate offering price of the Securities. The relative fault of the Company on
the one hand and of the Initial Purchasers on the other hand shall be determined
by reference to, among other things, whether the untrue or alleged untrue
statement of a material fact or the omission or alleged omission to state a
material fact relates to information supplied by the Company or by the Initial
Purchasers and the parties' relative intent, knowledge, access to information
and opportunity to correct or prevent such statement or omission. The Initial
Purchasers' respective obligations to contribute pursuant to this Section 8 are
several in proportion to the respective principal amount of Securities they have
purchased hereunder, and not joint.

          (e) The Company and the Initial Purchasers agree that it would not be
just or equitable if contribution pursuant to this Section 8 were determined by
pro rata allocation (even if the Initial Purchasers were treated as one entity
for such purpose) or by any other method of allocation that does not take
account of the equitable considerations referred to in Section 8(d). The amount
paid or payable by an indemnified party as a result of the losses, claims,
damages and liabilities referred to in Section 8(d) shall be deemed to include,
subject to the limitations set forth above, any legal or other expenses
reasonably incurred by such indemnified party in connection with investigating
or defending any such action or claim. Notwithstanding the provisions of this
Section 8, no Initial Purchaser shall be required to contribute any amount in
excess of the amount by which the total price at which the Securities resold by
it in the initial placement of such Securities were offered to investors exceeds
the amount of any damages that such Initial Purchaser has otherwise been
required to pay by reason of such untrue or alleged untrue statement or omission
or alleged omission. No person guilty of fraudulent misrepresentation (within
the meaning of Section 11(f) of the Securities Act) shall be entitled to
contribution from any person who was not guilty of such fraudulent
misrepresentation. The remedies provided for in this Section 8 are not

                                      16
<PAGE>
 
exclusive and shall not limit any rights or remedies which may otherwise be
available to any indemnified party at law or in equity.

          (f) The indemnity and contribution provisions contained in this
Section 8 and the representations, warranties and other statements of the
Company contained in this Agreement shall remain operative and in full force and
effect regardless of (i) any termination of this Agreement, (ii) any
investigation made by or on behalf of any Initial Purchaser or any person
controlling any Initial Purchaser or by or on behalf of the Company, its
officers or directors or any person controlling the Company and (iii) acceptance
of and payment for any of the Securities.

     9.   Termination.  This Agreement shall be subject to termination by notice
given by you to the Company, if (a) after the execution and delivery of this
Agreement and prior to the Closing Date (i) trading generally shall have been
suspended or materially limited on or by, as the case may be, any of the New
York Stock Exchange, the American Stock Exchange, the National Association of
Securities Dealers. Inc., the Chicago Board of Options Exchange, the Chicago
Mercantile Exchange or the Chicago Board of Trade, (ii) trading of any
securities of the Company shall have been suspended on any exchange or in any
over-the-counter market, (iii) a general moratorium on commercial banking
activities in New York shall have been declared by either Federal or New York
State authorities or (iv) there shall have occurred any outbreak or escalation
of hostilities or any change in financial markets or any calamity or crisis
that, in your judgment, is material and adverse and (b) in the case of any of
the events specified in clauses 9(a)(i) through 9(a)(iv), such event, singly or
together with any other such event, makes it, in your judgment, impracticable to
market the Securities on the terms and in the manner contemplated in the Final
Memorandum.

     10.  Effectiveness; Defaulting Initial Purchasers.  This Agreement shall
become effective upon the execution and delivery hereof by the parties hereto.

     If, on the Closing Date, or the Option Closing Date, as the case may be,
any one or more of the Initial Purchasers shall fail or refuse to purchase
Securities that it or they have agreed to purchase hereunder on such date, and
the aggregate principal amount of Securities which such defaulting Initial
Purchaser or Initial Purchasers agreed but failed or refused to purchase is not
more than one-tenth of the aggregate principal amount of Securities to be
purchased on such date, the other Initial Purchasers shall be obligated
severally in the proportions that the principal amount of Firm Securities set
forth opposite the names of all such non-defaulting Initial Purchasers, or in
such other proportions as you may specify, to purchase the Securities which such
defaulting Initial Purchaser or Initial Purchasers agreed but failed of refused
to purchase on such date; provided that in no event shall the principal amount
of Securities that any Initial Purchaser has agreed to purchase pursuant to this
Agreement be increased pursuant to this Section 10 by an amount in excess of
one-ninth of such principal amount of Securities without the written consent of
such Initial Purchaser.  If, on the Closing Date any Initial Purchaser or
Initial Purchasers shall fail or refuse to purchase Firm Securities which it or
they have agreed to purchase hereunder on such date and the aggregate principal
amount of Securities with respect to which such default occurs is more than one-
tenth of the aggregate principal amount of Firm Securities to be purchased on
such date, and arrangements

                                      17
<PAGE>
 
satisfactory to you and the Company for the purchase of such Firm Securities are
not made within 36 hours after such default, this Agreement shall terminate
without liability on the part of any non-defaulting Initial Purchaser or of the
Company.  In any such case either you or the Company shall have the right to
postpone the Closing Date, but in no event for longer than seven days, in order
that the required changes, if any, in the Final Memorandum or in any other
documents or arrangements may be effected.  If, on the Option Closing Date, any
Initial Purchaser or Initial Purchasers shall fail or refuse to purchase
Additional Securities and the aggregate principal amount of Additional
Securities with respect to which such default occurs is more than one-tenth of
the aggregate principal amount of Additional Securities to be purchased, the
non-defaulting Initial Purchasers shall have the option to (a) terminate their
obligation hereunder to purchase Additional Securities or (b) purchase not less
than the principal amount of Additional Securities that such non-defaulting
Initial Purchasers would have been obligated to purchase in the absence of such
default. Any action taken under this paragraph shall not relieve any defaulting
Initial Purchaser from liability in respect of any default of such Initial
Purchaser under this Agreement.

     If this Agreement shall be terminated by the Initial Purchasers, or any of
them, because of any failure or refusal on the part of the Company to comply
with the terms or to fulfill any of the conditions of this Agreement, or if for
any reason the Company shall be unable to perform its obligations under this
Agreement, the Company will reimburse the Initial Purchasers or such Initial
Purchasers as have so terminated this Agreement with respect to themselves,
severally, for all out-of-pocket expenses (including the fees and disbursements
of their counsel) reasonably incurred by such initial Purchasers in connection
with this Agreement or the offering contemplated hereunder.

     11.  Counterparts.  This Agreement may be signed in any number of
counterparts, each of which shall be an original, with the same effect as if the
signatures thereto and hereto were upon the same instrument.

     12.  Applicable Law.  This Agreement shall be governed by and construed in
accordance with the internal laws of the State of New York.

     13.  Headings.  The headings of the sections of this Agreement have been
inserted for convenience of reference only and shall not be deemed a part of
this Agreement.


                                      18
<PAGE>
 
                              Very truly yours,

                              Aviron



                                     /s/ J. Leighton Read, M.D.      
                              By:__________________________________________
                                    J. Leighton Read, M.D.
                                    Chief Executive Officer



Accepted as of the date hereof

Morgan Stanley & Co. Incorporated

Acting severally on behalf of themselves and
    the several Initial Purchasers named in
    Schedule I hereto.

By: Morgan Stanley & Co. Incorporated



     /s/ Catherine J. Friedman      
By:____________________________________
     Catherine J. Friedman
     Managing Director
<PAGE>
 
                                                                      SCHEDULE I


<TABLE>
<CAPTION>
                                            PRINCIPAL AMOUNT
                                           OF FIRM SECURITIES
            INITIAL PURCHASER               TO BE PURCHASED
- -----------------------------------------  ------------------
<S>                                        <C>
Morgan Stanley & Co. Incorporated........      $25,000,000.00
Bear Stearns & Co........................      $25,000,000.00
Credit Suisse First Boston Corporation...      $25,000,000.00
Hambrecht & Quist LLC....................      $25,000,000.00
 
 
 
 
                                               --------------
      Total..............................      $  100,000,000
                                               ==============
</TABLE>



                                       1
<PAGE>
 
                                                                       EXHIBIT A


                         OPINION OF COOLEY GODWARD LLP

     The opinion of the Cooley Godward LLP to be delivered pursuant to Section
5(c) of the Purchase Agreement shall be to the effect that:

     A.   The Company has been duly incorporated, is validly existing as a
corporation in good standing under the laws of the jurisdiction of its
incorporation, has the corporate power and authority to own its property and to
conduct its business as described in the Final Memorandum and, to such counsel's
knowledge, is duly qualified to transact business and is in good standing in
each jurisdiction in which the conduct of its business or its ownership or
leasing of property requires such qualification, except to the extent that the
failure to be so qualified or be in good standing would not have a material
adverse effect on the Company.

     B.   To such counsel's knowledge, the Company does not own or control,
directly or indirectly, any corporation, association or other entity.

     C.   The Purchase Agreement has been duly authorized, executed and
delivered by the Company.

     D.   The authorized and outstanding capital stock of the Company is as set
forth in the Final Memorandum on the dates set forth therein under the caption
"Capitalization."  The authorized capital stock of the Company conforms as to
legal matters to the description thereof contained in the Final Memorandum.

     E.   The shares of common stock outstanding on the Closing Date or Option
Closing Date have been duly authorized and are validly issued, fully paid and
non-assessable.

     F.   The Securities have been duly authorized by the Company and, when
executed and authenticated in accordance with the provisions of the Indenture
and delivered to and paid for by the Initial Purchasers in accordance with the
terms of the Purchase Agreement, will be valid and binding obligations of the
Company, except as may be limited by applicable bankruptcy, insolvency or
similar laws affecting creditors' rights generally and general principles of
equity, and will be entitled to the benefits of the Indenture and the
Registration Rights Agreement.

     G.   The Underlying Securities reserved for issuance upon conversion of the
Securities have been duly authorized and reserved and, when issued upon
conversion of the Securities in accordance with the terms of the Securities,
will be validly issued, fully paid and non-assessable and the issuance of the
Underlying Securities will not be subject to any preemptive or similar rights.

     H.   Each of the Indenture and the Registration Rights Agreement has been
duly authorized, executed and delivered by the Company.
<PAGE>
 
     I.  The execution and delivery by the Company of, and the performance by
the Company of its obligations under, the Purchase Agreement, the Indenture, the
Registration Rights Agreement and the Securities will not contravene any
provision of applicable law or the certificate of incorporation or bylaws of the
Company or, to such counsel's knowledge, any agreement or other instrument
binding upon the Company that is material to the Company or, to such counsel's
knowledge, any material judgment, order or decree of any governmental body,
agency or court having jurisdiction over the Company, and no consent, approval,
authorization or order of, or qualification with, any governmental body or
agency is required for the performance by the Company of its obligations under
the Purchase Agreement, the Indenture, the Registration Rights Agreement or the
Securities, except such as may be required by the securities or Blue Sky laws of
the various states in connection with the offer and sale of the Securities (as
to which such counsel expresses no opinion) and by Federal and state securities
laws with respect to the Company's obligations under the Registration Rights
Agreement.

     J.   Such counsel does not know of any legal or governmental proceedings
pending or threatened to which the Company is a party or to which any of the
properties of the Company is subject other than proceedings fairly summarized in
all material respects in the Final Memorandum and proceedings which such counsel
believes are not likely to have a material adverse effect on the Company, or on
the power or ability of the Company to perform its obligations under the
Purchase Agreement, the Indenture, the Registration Rights Agreement or the
Securities or to consummate the transactions contemplated by the Final
Memorandum.

     K.   The Company is not, and after giving effect to the offering and sale
of the Securities and the application of the proceeds thereof as described in
the Final Memorandum, will not be an "investment company" as such term is
defined in the Investment Company Act of 1940, as amended.

     L    To the knowledge of such counsel, there is no legal or beneficial
owner of any securities of the Company who has any rights, not effectively
satisfied or waived, to require registration of any shares of capital stock of
the Company in connection with the filing of the registration statement on Form
S-3 pursuant to the terms of the Registration Rights Agreement.

     M.   The statements in the Final Memorandum under the captions "Description
of  Notes," "Description of Capital Stock," and "Transfer Restrictions," insofar
as such statements constitute summaries of the legal matters, documents or
proceedings referred to therein, fairly summarize the matters referred to
therein to the extent as would be required if the Final Memorandum were a
prospectus included in a Registration Statement on Form S-1 under the Securities
Act.

     N.   The statements in the Final Memorandum under the caption "Certain
Federal Income Tax Considerations," insofar as such statements represent matters
of law or legal conclusions, and subject to the qualifications and limitations
contained in that discussion, are accurate and fairly summarize the material
United States federal income tax considerations relevant to a purchase of the
Securities.

                                       2
<PAGE>
 
     O.   Based upon the representations, warranties and agreements of the
Company in Sections 1(q), 1(r), 1(s), 6(f), 6(g) and 6(j) of the Purchase
Agreement and of the Initial Purchasers in Section 7 of the Purchase Agreement,
it is not necessary in connection with the offer, sale and delivery of the
Securities to the Initial Purchasers under the Purchase Agreement or in
connection with the initial resale of such Securities by the Initial Purchasers
in accordance with Section 7 of the Purchase Agreement to register the
Securities under the Securities Act or to qualify the Indenture under the Trust
Indenture Act of 1939, it being understood that no opinion is expressed as to
any subsequent resale of any Security or Underlying Security.

     P.   No consent, approval, authorization or order of or qualification with
any court, government or governmental agency or body having jurisdiction over
the Company, or over any of its properties or operations is necessary in
connection with the consummation by the Company of the transactions contemplated
by the Purchase Agreement, except such as have been obtained under the
Securities Act and the Exchange Act or such as may be required under state or
other securities or Blue Sky laws in connection with the purchase and the
distribution of the Securities by the Initial Purchasers (and such counsel
expresses no opinion as to state securities or Blue Sky laws).

     Q.   To such counsel's knowledge, the Company is not presently (a) in
material violation of its charter or bylaws, or (b) subject to any material
order, writ or decree applicable specifically to the Company of any court or
governmental agency or body having jurisdiction over the Company, or over any of
its properties or operations.

     R.   Except as disclosed in the Final Memorandum under the caption "Risk
Factors --Uncertainty of Protection of Patents and Proprietary Rights;
Dependence on Trade Secrets,"  to the best of such counsel's knowledge, the
Company has received no notice of any infringement or misappropriation by a
third party of any patent in Section C of the Patent Portfolio attached hereto
as Exhibit F (the "Patent Portfolio") or notice of any infringement or
misappropriation by the Company of any patents, trade secrets, trademarks, trade
names, copyrights or other proprietary rights of a third party, other than
notices of opposition to the Company's trademark applications for the mark
"AVIRON" in Germany and a notice of potential infringement for such trademark
application in France.

     S.   Except as disclosed in the Prospectus under the caption "Risk Factors
- -- Uncertainty of Protection of Patents and Proprietary Rights; Dependence on
Trade Secrets," to the best of such counsel's knowledge, the Company or its
licensor is the sole assignee for each patent and patent application listed in
Section C of the Patent Portfolio.  Except as otherwise noted in Section C of
the Patent Portfolio attached hereto, for each of the United States patents and
patent applications, the assignments by the named inventors have been submitted
to the United States Patent and Trademark Office ("USPTO") and those assignments
have been recorded in the Patent Office's title records.  However, in one or
more of the patents and patent applications listed in Section C of the Patent
Portfolio, the United States government may hold a nonexclusive, royalty free
license as a result of providing research funding.

                                       3
<PAGE>
 
     T.   To such counsel's knowledge, the Company's United States patent
applications listed in Section C of the Patent Portfolio have been prepared and
filed in the USPTO in a form and with accompanying papers that are acceptable to
the USPTO for the purposes of according each such application a filing date and
serial number, and of placing each such application in condition for eventual
examination on the merits as to patentability.  For each such U.S. application,
such counsel is not aware of any material defect of form in preparation or
filing.

     U.   To such counsel's knowledge, as to each of the Company's foreign
patent applications listed in Section C of the Patent Portfolio, the
applications have either (a) except as noted in Section C of the Patent
Portfolio attached hereto, been submitted to patent firms in the respective
foreign countries with instructions to file the applications in the patent
offices of those countries naming the Company as the applicant of record, or (b)
as to certain Patent Cooperation Treaty applications, been submitted directly to
the relevant receiving office naming the Company as the applicant of record.  To
the best of such counsel's knowledge and except as noted in Section C of the
Patent Portfolio, as to each of such applications, the Company has not received
notice from any foreign filing authority of any material defect of form in
preparation or filing.

     V.   The statements contained in the Registration Statement and Prospectus
under the captions "Risk Factors--Uncertainty of Protection of Patents and
Proprietary Rights; Dependence Upon Trade Secrets" and "Business--Patents and
Proprietary Rights" as they pertain to Section C of the Patent Portfolio,
insofar as such statements constitute matters of law, are a fair and accurate
summary of the matters set forth therein, as required under the Act and
applicable Rules and Regulations.

     W.   Based upon such counsel's participation in the preparation of the
Final Memorandum (and any amendments or supplements thereto) and review and
discussion of the contents thereof and review of the documents incorporated by
reference therein, but without independent check or verification, nothing has
come to the attention of such counsel to cause him or her to believe that the
Final Memorandum or any information incorporated by reference therein (other
than the financial statements, schedules and other financial and statistical
information included therein, as to which such counsel may make no statement),
as of the date thereof and as of the Closing Date contained or contains any
untrue statement of a material fact or omitted or omits to state a material fact
required to be stated therein or necessary to make the statements therein, in
light of the circumstances under which they were made, not misleading.

                                       4
<PAGE>
 
                                                                       EXHIBIT B


                         OPINION OF PENNIE AND EDMONDS


     A.   To the best of such counsel's knowledge, except as otherwise disclosed
in Exhibit F attached to such opinion, the Company is licensed to use, or owns,
each patent and patent application described in the Prospectus, as listed in
Section A of the Patent Portfolio;

     B.   To the best of such counsel's knowledge, except as otherwise described
in Exhibit F attached to such opinion, no third party has any rights to the
patents and patent applications listed in Schedule A of the Patent Portfolio;

     C.   To the best of such counsel's knowledge, there are no material legal
or governmental proceedings, pending or threatened, with respect to any issued
United States patent listed in Section A of the Patent Portfolio;

     D.   To the best of such counsel's knowledge, the Company has not received
any notice with respect to the potential infringement of, conflict with or
proceedings against, any patents, trademarks, copyrights, trade secrets, or
proprietary rights, of others;

     E.   To the best of such counsel's knowledge, no third parties are
infringing any of the United States patents listed in Schedule A of the Patent
Portfolio;

     F.   The Company's United States patent applications listed in Section A of
the Patent Portfolio have been prepared and filed in the USPTO in a form and
with accompanying papers that are acceptable to the USPTO for the purposes of
according each such application a filing date and serial number, and of placing
each such application in condition for eventual examination on the merits as to
patentability.  For each such United States application an Official Filing
Receipt has been received from the USPTO.  As to each of such applications, such
counsel is not aware of any material defect of form in preparation or filing;
and the patent applications in Section A of  the Patent Portfolio are being
diligently pursued;

     G.   The statements contained in the Registration Statement and Prospectus
under the captions "Risk Factors--Uncertainty of Protection of Patents and
Proprietary Rights; Dependence Upon Trade Secrets" and "Business--Patents and
Proprietary Rights" as they pertain to Section A of the Patent Portfolio and
United States patent rights, insofar as such statements constitute matters of
law, are a fair and accurate summary of the matters set forth therein; and

          In addition such counsel shall state that such counsel has
participated in conferences with officials and other representatives of the
Company, the Representatives, Underwriters' Counsel and the independent
certified public accountants of the Company, at which such conferences the
contents of the Registration Statement and Prospectus and related matters were
discussed, and
<PAGE>
 
although they have not verified the accuracy or completeness of the statements
contained in the Registration Statement or the Prospectus, nothing has come to
the attention of such counsel which leads such counsel to believe that, at the
time the Registration Statement became effective and at all times subsequent
thereto up to and on the Closing Date and on any later date on which Option
Shares are to be purchased, the statements relating to United States patents and
patent applications listed in Section A of the Patent Portfolio in the
Registration Statement and any amendment or supplement thereto (other than
financial statements including supporting schedules and other financial and
statistical information derived therefrom, as to which such counsel need express
no comment) contained any untrue statement of a material fact or omitted to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading, or at the Closing Date or any later date on
which Option Shares are to be purchased, as the case may be, the statements
relating to United States patents listed in Section A of the Patent Portfolio in
the Prospectus, and any amendment or supplement thereto, (except aforesaid)
contained any untrue statement of a material fact or omitted to state a material
fact required to be stated therein or necessary to make the statements therein,
in light of the circumstances under which they were made, not misleading.

                                       2
<PAGE>
 
                                                                       EXHIBIT C


              OPINION OF MARSHALL O'TOOLE GERSTEIN MURRAY & BORUN


     A.   To the best of such counsel's knowledge, such knowledge is being based
upon the files of such firm, except as otherwise disclosed in the Offering
Memorandum, there are no legal or governmental proceedings relating to patent
rights owned, licensed, or used by the Company pending against the Company or
any third party and, except for the Company's pending patent applications, to
the best of such counsel's knowledge, there are no legal or governmental
proceedings relating to patent rights owned, licensed or used by third parties
pending against the Company.  To the best of such counsel's knowledge, other
than those disclosed in the Offering Memorandum, no such proceedings are
threatened or contemplated by governmental authorities or others;

     B.   To the best of such counsel's knowledge, such knowledge being based
upon the files of such firm, the Company has no notice of any infringement by a
third party of any patent owned or used by the Company; and to the best of such
counsel's knowledge, such knowledge being based upon the files of such firm, the
Company has not received notice of any claims of infringement by the Company of
any patent owned or used by a third party;

     C.   To the best of such counsel's knowledge, such knowledge is being based
upon the files of such firm, the Company or one of its licensors is the sole
assignee for each patent and patent application listed in Section B of the
Patent Portfolio. To the best of such counsel's knowledge, the assignments by
the named inventors have been submitted to the USPTO and those assignments have
been recorded in the assignment records of the USPTO. However, in one or more of
the patents and patent applications listed in Section B of the Patent Portfolio,
the United States government may hold a nonexclusive, royalty free license as a
result of providing research funding;

     D.   To the best of such counsel's knowledge, such knowledge is being based
upon the files of such firm, the Company's United States patent applications
listed in Section B of the Patent Portfolio have been prepared and filed in the
USPTO in a form and with accompanying papers that are acceptable to the USPTO
for the purposes of according each such application a filing date and serial
number, and of placing each such application in condition for eventual
examination on the merits as to patentability. For each such United States
application, except as otherwise noted in Exhibit F attached to this opinion, an
Official Filing Receipt has been received from the USPTO. As to each of such
applications, such counsel is not aware of any material defect of form in
preparation or filing. However, there is no assurance that patents will issue
from any pending United States application, or that any claims will be allowed
without amendment. Neither is there any assurance that a patent will issue
without appeal to the Board of Patent Appeals and Interferences or to the
Federal Courts;

     E.   To the best of such counsel's knowledge, such knowledge is being based
upon the files of such firm, each of the Company's foreign patents and patent
applications listed in Section B
<PAGE>
 
of the Patent Portfolio has been submitted to patent firms in the respective
foreign countries with instructions to file the applications in the patent
offices of those countries naming the Company or one its licensors as applicant
and/or owner of record.  The Patent Cooperation Treaty applications have been
submitted directly to the relevant patent examining authority of those countries
naming the Company or one of its licensors as the applicant and/or owner of
record.  In each such application, written confirmation has been received that
the application has been accepted for filing by such patent office, or patent
examining authority.  There is no assurance that the patent offices of the
respective countries will not reject the claims of the foreign patent
applications as being unpatentable, or that any claims will be allowed without
amendment, nor is there any assurance that these patent authorities will
ultimately conclude that the foreign patent applications meet all requirements
for patentability.  Such counsel is not aware of any material defect of form in
preparation or filing.  To the best of such counsel's knowledge, other than two
oppositions filed in the European Patent Office against European Patent No.
500,917 corresponding to Aviron reference no. 5005-EP as listing in Section B of
the Patent Portfolio, there are no legal or governmental proceedings relating to
any foreign patent rights or foreign patent applications owned, licensed or sued
by the Company pending against the Company or any third party and, except for
prosecution of pending patent applications, to the best of such counsel's
knowledge, there are no legal or governmental proceedings relating to any
foreign patent rights or foreign patent applications owned, licensed or used by
third parties pending against Aviron.  To the best of such counsel's knowledge,
other than otherwise disclosed in the Offering Memorandum, no such proceedings
are threatened or contemplated by governmental authorities or others;

     F.   The patent applications in Section B of the Patent Portfolio are being
diligently pursued;

     G.   The statements contained in the Offering Memorandum under the captions
"Risk Factors--Uncertainty of Protection of Patents and Proprietary Rights;
Dependence of Trade Secrets" and "Business--Patents and Proprietary Technology"
insofar as such statements constitute matters of law, are a fair and accurate
summary of the matters set forth therein; and

          In addition, such counsel shall state that such counsel has
participated in conferences with officials and other representatives of the
Company, the Initial Purchasers, Counsel to the Initial Purchasers and the
Company, and the independent certified public accountants of the Company, at
which such conferences the contents of the Offering Memorandum and related
matters were discussed, and although they have not verified the accuracy or
completeness of the statements contained in the Offering Memorandum, nothing has
come to the attention of such counsel which leads such counsel to believe that,
at the time of the Final Memorandum and at all times subsequent thereto up to
and on the Closing Date and on any later date on which Option Shares are to be
purchased, the statements relating to patents and patent applications listed in
Section B of the Patent Portfolio in the Offering Memorandum and any amendment
or supplement thereto (other than financial statements including supporting
schedules and other financial and statistical information derived therefrom, as
to which such counsel need express no comment) contained any untrue statement of
a material fact or omitted to state a material fact required to be stated
therein or necessary to make the statements therein not misleading, or at the
Closing Date or any later date on

                                       2
<PAGE>
 
which Option Shares are to be purchased, as the case may be, the statements
relating to patents and patent applications listed in Section B of the Patent
Portfolio in the Prospectus, and any amendment or supplement thereto, (except
aforesaid) contained any untrue statement of a material fact or omitted to state
a material fact required to be stated therein or necessary to make the
statements therein, in light of the circumstances under which they were made,
not misleading.


                                       3
<PAGE>
 
                                                                       EXHIBIT D


                  OPINION OF WILSON SONSINI GOODRICH & ROSATI

     The opinion of Wilson Sonsini Goodrich & Rosati to be delivered pursuant to
Section 5(d) of the Purchase Agreement shall be to the effect that:

     A.   The Purchase Agreement has been duly authorized, executed and
delivered by the Company.

     B.   The Securities have been duly authorized by the Company and, when
executed and authenticated in accordance with the provisions of the Indenture
and delivered to and paid for by the Initial Purchasers in accordance with the
terms of the Purchase Agreement, will be valid and binding obligations of the
Company, enforceable in accordance with their terms, subject to applicable
bankruptcy, insolvency or similar laws affecting creditors' rights generally and
general principles of equity, and will be entitled to the benefits of the
Indenture and the Registration Rights Agreement.

     C.   The Underlying Securities reserved for issuance upon conversion of the
Securities have been duly authorized and reserved and, when issued upon
conversion of the Securities in accordance with the terms of the Securities,
will be validly issued, fully paid and non-assessable, and the issuance of the
Underlying Securities will not be subject to any preemptive or similar rights.

     D.   Each of the Indenture and the Registration Rights Agreement has been
duly authorized, executed and delivered by, and is a valid and binding agreement
of, the Company, enforceable in accordance with its terms, subject to applicable
bankruptcy, insolvency or similar laws affecting creditors' rights generally and
general principles of equity and except as rights to indemnification and
contribution under the Registration Rights Agreement may be limited under
applicable law.

     E.   The statements in the Final Memorandum under the captions "Description
of Notes", "Plan of Distribution" and "Transfer Restrictions," insofar as such
statements constitute summaries of the legal matters, documents or proceedings
referred to therein, fairly summarize the matters referred to therein.

     F.   Such counsel has no reason to believe that (except for financial
statements and schedules and other financial and statistical data as to which
such counsel need not express any belief) the Final Memorandum when issued
contained, or as of the date such opinion is delivered contains, any untrue
statement of a material fact or omitted or omits to state a material fact
necessary in order to make the statements therein, in the light of the
circumstances under which they were made, not misleading.

     G.   Based upon the representations, warranties and agreements of the
Company in Sections 1(q), 1(r), 1(t), 6(f), 6(g) and 6(j) of the Purchase
Agreement and of the Initial Purchasers in
<PAGE>
 
Section 7 of the Purchase Agreement, it is not necessary in connection with the
offer, sale and delivery of the Securities to the Initial Purchasers under the
Purchase Agreement or in connection with the initial resale of such Securities
by the Initial Purchasers in accordance with Section 7 of the Purchase Agreement
to register the Securities under the Securities Act of 1933 or to qualify the
Indenture under the Trust Indenture Act of 1939, it being understood that no
opinion is expressed as to any subsequent resale of any Security or Underlying
Security.

     With respect to paragraph G above, Wilson Sonsini Goodrich & Rosati may
state that their opinion and belief are based upon their participation in the
preparation of the Final Memorandum (and any amendments or supplements thereto)
and review and discussion of the contents thereof (including the review of, but
not participation in the preparation of, the incorporated documents), but are
without independent check or verification except as specified.


                                       2
<PAGE>
 
                                                                       EXHIBIT E


                   OPINION OF REED SMITH SHAW AND MCCLAY LLP


     A.   Each of the Indenture and the Registration Rights Agreement is a valid
and binding agreement of the Company, enforceable against the Company in
accordance with its terms except as (A) the enforceability thereof may be
limited by bankruptcy, insolvency or similar laws affecting creditors' rights
generally, (B) rights of acceleration, certain waivers and the availability of
equitable remedies may be limited by equitable principles of general
applicability and (C) rights to indemnification and contribution may be limited
under applicable law.

     B.   When executed and authenticated in accordance with the provisions of
the Indenture and delivered to and paid for by the Initial Purchasers in
accordance with the terms of the Purchase Agreement, the Notes will be valid and
binding obligations of the Company, enforceable against the Company in
accordance with their terms except as (A) the enforceability thereof may be
limited by bankruptcy, insolvency or similar laws affecting creditors' rights
generally, (B) rights of acceleration, certain waivers and the availability of
equitable remedies may be limited by equitable principles of general
applicability and (C) rights to imdemnification and contribution may be limited
under applicable law.
<PAGE>
 
                                                                       EXHIBIT F


                         SECTION A - (PENNIE & EDMONDS)

<TABLE>
<CAPTION>
                  AVIRON REFERENCE NO.   AVIRON REFERENCE NO.
                  --------------------   --------------------
                       <S>                     <C> 
                         5009B                  5010B
                         5009F                  5011A
                         5009G                  5011A-DIV
                         5009H                  5015
                         5009G/DIV              5015-DIV
</TABLE>
<PAGE>
 
                                                              EXHIBIT F (CONT'D)


                         SECTION B - (MARSHALL O'TOOLE)

<TABLE>
<CAPTION>
                AVIRON REFERENCE NO.       AVIRON REFERENCE NO.
                --------------------       --------------------
                   <S>                     <C>
                     5001                          5005
                     5001-CA                       5005-AU
                     5001-EP                       5005-CA
                     5002-CA                       5005-JP
                     5002-JP                       5005-EP
                     5002-JP/DIV                   5005A
                     5002EP                        5005-AT
                     5002B                         5005-BE
                     5002C                         5005-CH
                     5002C-AU                      5005-DE
                     5002C-CA                      5005-DK
                     5002C-EP                      5005-ES
                     5002C-JP                      5005-FR
                     5002C-ZA                      5005-GB
                     5002E                         5005-GR
                     5002G                         5005-IT
                     5003A                         5005-LU
                     5004A                         5005-NL
                                                   5005-SE
                                                   5006-AU
                                                   5006-CA
                                                   5006-EP
                                                   5006-JP
 
                                                   5006B
                                                   5006C
                                                   5007-PCT
                                                   5007-KR
                                                   5007-EP
                                                   5007A
</TABLE>


                                       2
<PAGE>
 
                                                              EXHIBIT F (CONT'D)


                       SECTION C - (COOLEY GODWARD LLP)

                             AVIRON REFERENCE NO.
                             --------------------
                                     5016
                                     5017
                                     5018
                                     5018-IN
                                     5018-MY
                                     5019
                                     5019-PCT
                                     5021
                                     5021-PCT
                                     5022
                                     5023
                                     5023-PCT
                                     5032

                                       3

<PAGE>
                                                                     EXHIBIT 5.1
 
April 3, 1998

Aviron
297 North Bernardo Avenue
Mountain View, CA 94043

RE: AVIRON FORM S-3

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection 
with the filing by Aviron (the "Company") of a Registration Statement on Form 
S-3 (the "Registration Statement") with the Securities and Exchange Commission, 
including a prospectus (the "Prospectus"), covering the offering of 2,314,286 
shares of the Company's Common Stock, with a par value of $0.001 (the "Shares") 
to be sold by one certain stockholder as described in the Registration 
Statement. Of such Shares, 1,714,286 were issued by the Company pursuant to a 
Common Stock Purchase Agreement by and between the Company and Biotech Target, 
S.A., dated as of March 27, 1997, and 600,000 were issued upon conversion of 
Series C Preferred Stock originally purchased in October 1995. Defined terms 
used herein shall have the meanings attributed to such terms in the Registration
Statement unless otherwise stated herein.

In connection with this opinion, we have examined and relied upon the 
Registration Statement and related Prospectus, the Company's Amended and 
Restated Certificate of Incorporation, the Company's Restated Bylaws, and the 
originals or copies certified to our satisfaction of such documents, records, 
certificates, memoranda and other instruments as in our judgment are necessary 
or appropriate to enable us to render the opinion expressed below. We have 
assumed the genuineness and authenticity of all documents submitted to us as 
copies thereof, and the due execution and delivery of all documents where due 
execution and delivery are a prerequisite to the effectiveness thereof.
    
On the basis of the foregoing, and in reliance thereon, we are of the opinion 
that the Shares are validly issued, fully paid, and nonassessable.      

We consent to the reference to our firm under the caption "Legal Matters" in the
Prospectus included in the Registration Statement and to the filing of this 
opinion as an exhibit to the Registration Statement.


Very truly yours,

Cooley Godward LLP


By: /s/ Robert J. Brigham
   -----------------------
        Robert J. Brigham

         

<PAGE>
 
                                                                    EXHIBIT 23.1

              CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS
              ---------------------------------------------------


    
        We consent to the reference to our firm under the caption "Experts" in
Amendment No. 2 to the Registration Statement (Form S-3, No. 333-41649) and
related Prospectus of Aviron for the registration of 2,314,286 shares of its
common stock and to the incorporation by reference therein of our report dated
February 13, 1998, with respect to the financial statements of Aviron included
in its Annual Report (Form 10-K), as amended, for the year ended December 31,
1997, filed with the Securities and Exchange Commission.     

         

Palo Alto, California
     
April 2, 1998      

<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<RESTATED>
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   9-MOS
<FISCAL-YEAR-END>                          DEC-31-1996
<PERIOD-START>                             JAN-01-1996
<PERIOD-END>                               SEP-30-1996
<CASH>                                           3,818
<SECURITIES>                                         0
<RECEIVABLES>                                      500
<ALLOWANCES>                                         0
<INVENTORY>                                          0
<CURRENT-ASSETS>                                 7,044
<PP&E>                                           3,446
<DEPRECIATION>                                  (1,096)
<TOTAL-ASSETS>                                   9,486
<CURRENT-LIABILITIES>                            2,913
<BONDS>                                              0
                                0
                                     40,028
<COMMON>                                         2,355
<OTHER-SE>                                     (36,764)
<TOTAL-LIABILITY-AND-EQUITY>                     9,486
<SALES>                                              0
<TOTAL-REVENUES>                                   688
<CGS>                                                0
<TOTAL-COSTS>                                        0
<OTHER-EXPENSES>                                13,170
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                                 138
<INCOME-PRETAX>                                (12,740)
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                            (12,740)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                   (12,740)
<EPS-PRIMARY>                                    (1.48)
<EPS-DILUTED>                                    (1.48)
        

</TABLE>

<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE
CONSOLIDATED BALANCE SHEETS, STATEMENTS OF OPERATIONS AND STATEMENTS OF CASH
FLOWS INCLUDED IN THE COMPANY'S FORM 10-Q FOR THE PERIOD ENDED MARCH 31, 1997,
AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS AND
NOTES THERETO.
</LEGEND>
<RESTATED>
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   3-MOS
<FISCAL-YEAR-END>                          DEC-31-1997
<PERIOD-START>                             JAN-01-1997
<PERIOD-END>                               MAR-31-1997
<CASH>                                          23,854
<SECURITIES>                                     3,874
<RECEIVABLES>                                      305
<ALLOWANCES>                                         0
<INVENTORY>                                          0
<CURRENT-ASSETS>                                28,722
<PP&E>                                           3,622
<DEPRECIATION>                                  (1,405)
<TOTAL-ASSETS>                                  31,027
<CURRENT-LIABILITIES>                            2,017
<BONDS>                                              0
                                0
                                          0
<COMMON>                                            13
<OTHER-SE>                                      28,177
<TOTAL-LIABILITY-AND-EQUITY>                    31,027
<SALES>                                              0
<TOTAL-REVENUES>                                   305
<CGS>                                                0
<TOTAL-COSTS>                                        0
<OTHER-EXPENSES>                                 5,451
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                                  53
<INCOME-PRETAX>                                 (4,977)
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                             (4,977)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                    (4,977)
<EPS-PRIMARY>                                    (0.44)
<EPS-DILUTED>                                    (0.44)
        

</TABLE>

<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE
CONSOLIDATED BALANCE SHEETS, STATEMENTS OF OPERATIONS AND STATEMENTS OF CASH
FLOWS INCLUDED IN THE COMPANY'S FORM 10-Q FOR THE PERIOD ENDED JUNE 30, 1997,
AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS AND
NOTES THERETO.
</LEGEND>
<RESTATED>
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   6-MOS
<FISCAL-YEAR-END>                          DEC-31-1997
<PERIOD-START>                             JAN-01-1997
<PERIOD-END>                               JUN-30-1997
<CASH>                                          13,305
<SECURITIES>                                     9,021
<RECEIVABLES>                                      424
<ALLOWANCES>                                         0
<INVENTORY>                                          0
<CURRENT-ASSETS>                                23,557
<PP&E>                                           3,779
<DEPRECIATION>                                  (1,565)
<TOTAL-ASSETS>                                  25,557
<CURRENT-LIABILITIES>                            2,315
<BONDS>                                              0
                                0
                                          0
<COMMON>                                            13
<OTHER-SE>                                      22,930
<TOTAL-LIABILITY-AND-EQUITY>                    25,995
<SALES>                                              0
<TOTAL-REVENUES>                                   414
<CGS>                                                0
<TOTAL-COSTS>                                        0
<OTHER-EXPENSES>                                11,518
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                                  98
<INCOME-PRETAX>                                (10,625)
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                            (10,625)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                   (10,625)
<EPS-PRIMARY>                                    (0.87)
<EPS-DILUTED>                                    (0.87)
        

</TABLE>

<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE
CONSOLIDATED BALANCE SHEETS, STATEMENTS OF OPERATIONS AND STATEMENTS OF CASH
FLOWS, INCLUDED IN THE COMPANY'S FORM 10-Q FOR THE PERIOD ENDED SEPTEMBER 30,
1997, AND ITS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL
STATEMENTS AND NOTES THERETO.
</LEGEND>
<RESTATED>
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   9-MOS
<FISCAL-YEAR-END>                          DEC-31-1997
<PERIOD-START>                             JAN-01-1997
<PERIOD-END>                               SEP-30-1997
<CASH>                                          50,335
<SECURITIES>                                    34,899
<RECEIVABLES>                                       29
<ALLOWANCES>                                         0
<INVENTORY>                                          0
<CURRENT-ASSETS>                                85,934
<PP&E>                                           4,413
<DEPRECIATION>                                  (1,729)
<TOTAL-ASSETS>                                  89,127
<CURRENT-LIABILITIES>                            3,577
<BONDS>                                              0
                                0
                                          0
<COMMON>                                            16
<OTHER-SE>                                      84,910
<TOTAL-LIABILITY-AND-EQUITY>                    89,127
<SALES>                                              0
<TOTAL-REVENUES>                                   446
<CGS>                                                0
<TOTAL-COSTS>                                        0
<OTHER-EXPENSES>                                18,314
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                                 141
<INCOME-PRETAX>                                (16,720)
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                            (16,720)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                   (16,720)
<EPS-PRIMARY>                                    (1.29)
<EPS-DILUTED>                                    (1.29)
        

</TABLE>


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