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                                                                Exhibit 10.5
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                          INTROGEN THERAPEUTICS, INC.

                            SERIES C PREFERRED STOCK

                               PURCHASE AGREEMENT


                              301 Congress Avenue
                                   Suite 2025
                              Austin, Texas 78701



<PAGE>   2


                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                     Page

<S>                                                                                  <C>
 1.       Purchase and Sale of Stock..................................................1

          1.1         Authorization...................................................1
          1.2         Sales of Preferred..............................................1

 2.       Closing Date; Delivery......................................................1

          2.1         Closing Date....................................................1
          2.2         Delivery........................................................1
          2.3         Subsequent Sales................................................1

 3.       Representations and Warranties of the Company...............................2

          3.1         Organization, Good Standing and Qualification...................2
          3.2         Capitalization..................................................2
          3.3         Subsidiaries....................................................3
          3.4         Authorization...................................................3
          3.5         Valid Issuance of Preferred and Common Stock....................3
          3.6         Governmental Consents...........................................3
          3.7         Litigation......................................................3
          3.8         Employees.......................................................4
          3.9         Patents and Trademarks..........................................4
          3.10        Compliance with Other Instruments...............................4
          3.11        Adverse Agreements..............................................5
          3.12        Disclosure......................................................5
          3.13        Title to Property and Assets....................................5
          3.14        Financial Statements............................................5
          3.15        Employee Benefit Plans..........................................6
          3.16        Tax Returns, Payments and Elections.............................6
          3.17        Labor Agreements and Actions....................................6
          3.18        Offering........................................................6

 4.       Representations and Warranties of the Investors.............................6

          4.1         Authorization...................................................6
          4.2         Purchase Entirely for Own Account...............................6
          4.3         Disclosure of Information.......................................7
          4.4         Investment Experience...........................................7
          4.5         Accredited Investor.............................................7
          4.6         Residence.......................................................7
</TABLE>



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<TABLE>
<S>                                                                                  <C>
          4.7         Restricted Securities...........................................7
          4.8         Further Limitations on Disposition..............................7
          4.9         Legends.........................................................8

5.        Conditions to Closing of Investors..........................................8

          5.1         Representations and Warranties Correct..........................8
          5.2         Covenants.......................................................8
          5.3         Blue Sky........................................................8
          5.4         Restated Certificate............................................9
          5.5         Minimum Purchase Amount.........................................9

 6.       Conditions to Closing of Company............................................9

          6.1         Representations.................................................9
          6.2         Blue Sky........................................................9
          6.3         Restated Certificate............................................9

 7.       Registration Rights.........................................................9

          7.1         Definitions.....................................................9
          7.2         Request for Registration.......................................10
          7.3         Company Registration...........................................11
          7.4         Obligations of the Company.....................................12
          7.5         Furnish Information............................................13
          7.6         Expenses of Demand Registration................................13
          7.7         Expenses of Company Registration...............................13
          7.8         Underwriting Requirements......................................14
          7.9         Delay of Registration..........................................14
          7.10        Indemnification................................................14
          7.11        Reports Under Securities Exchange Act of 1934..................16
          7.12        Form S-3 Registration..........................................16
          7.13        Assignment of Registration Rights..............................17
          7.14        Limitations on Subsequent Registration Rights..................17
          7.15        "Market Stand-Off" Agreement...................................18
          7.16        Amendment of Registration Rights and Information Rights........18
          7.17        Termination of Registration Rights.............................19
          7.18        Prior Registration Rights......................................19

 8.       Miscellaneous..............................................................19

          8.1         Survival of Warranties.........................................19
          8.2         Successors and Assigns.........................................19
          8.3         Governing Law..................................................19
</TABLE>


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<TABLE>
<S>                                                                                  <C>
          8.4         Counterparts...................................................19
          8.5         Titles and Subtitles...........................................19
          8.6         Notices........................................................19
          8.7         Expenses.......................................................20
          8.8         Amendments and Waivers.........................................20
          8.9         Severability...................................................20
          8.10        Aggregation of Stock...........................................20
</TABLE>



EXHIBITS

A.        [omitted]



                                     -iii-

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                       PREFERRED STOCK PURCHASE AGREEMENT



         THIS PREFERRED STOCK PURCHASE AGREEMENT is made by and between Introgen
Therapeutics, Inc., a Delaware corporation (the "Company"), and the investors
listed on the signature pages attached hereto (the "Investors"). This Agreement
is effective as of the date on which the Company has sold at least $1,000,000
of Series C Preferred Stock to an Investor.

         THE PARTIES HEREBY AGREE AS FOLLOWS:

          1.      Purchase and Sale of Stock.

                  1.1 Authorization. The Company will authorize the sale and
issuance of up to 1,183,000 shares of its Series C Preferred Stock (the "Series
C Preferred") having the rights, privileges and preferences as set forth in the
Restated Certificate of Incorporation (the "Restated Certificate") in the form
attached to this Agreement as Exhibit A.

                  1.2 Sales of Preferred. Subject to the terms and conditions
hereof, the Company will issue and sell to each Investor, and each Investor
shall separately purchase from the Company at the Closing (defined below) the
number of shares set forth beneath their signature page to this agreement at
the per share purchase price of $8.65. (The aggregate shares of Series C
Preferred Stock to be sold to the Investors hereunder are hereinafter referred
to as the "Shares"). No funds taken by an Investor for deposit in an escrow
account with Texas Commerce Bank, N.A. shall be released from such escrow
account until all conditions to closing set forth herein have been satisfied.

          2.      Closing Date; Delivery.

                  2.1 Closing Date. The first closing of the sale of the Series
C Preferred hereunder shall take place at such time and place upon which the
Company and the purchasers of at least $1,000,000 of Series C Preferred shall
agree (a "Closing"). The date of a Closing is hereinafter referred to as the
"Closing Date."

                  2.2 Delivery. At a Closing, the Company will deliver to each
Investor purchasing at such closing a certificate, registered in the Investors'
name, representing the number of shares of Series C Preferred to be purchased
by such Investor against payment of the purchase price therefor by check
payable to the Company or by wire transfer per the Company's wiring
instructions.

                  2.3 Subsequent Sales. Following the date of the first Closing
but not after March 31, 1996, the Company may sell up to the balance of the
1,183,000 authorized shares of Series C Preferred Stock which have not been
previously sold. Each such sale shall be considered a "Closing" hereunder and
each purchaser shall be deemed an "Investor" hereunder and shall append a
signature page to this Agreement.



<PAGE>   6



         3.       Representations and Warranties of the Company. Except as set
forth in the Confidential Private Placement Memorandum previously delivered to
each Investor, which disclosure (particularly the section entitled "Risk
Factors") shall modify the following representations and warranties, the
Company hereby represents and warrants:

                  3.1 Organization, Good Standing and Qualification. The
Company is a corporation duly organized, validly existing and in good standing
under the laws of the State of Delaware. The Company has all requisite
corporate power and authority to own and operate its properties and assets, to
carry on its business as now conducted and as proposed to be conducted, to
enter into this Agreement and to sell the Shares and carry out the other
transactions contemplated hereunder. The Company is duly qualified to transact
business and is in good standing in each jurisdiction in which the failure so
to qualify would have a material adverse effect on its business or properties.

                  3.2 Capitalization. The authorized capital of the Company
consists, or will consist prior to the first Closing, of:

                           (a) 6,308,523 shares of Preferred Stock ("Preferred
Stock"), of which 3,011,423 shares have been designated Series A Preferred
Stock, 2,114,100 shares have been designated Series B Preferred Stock and
1,183,000 shares have been designated Series C Preferred Stock. Prior to the
first Closing, there will be 3,011,423 shares of issued and outstanding Series
A Preferred Stock and 787,500 issued and outstanding shares of Series B
Preferred Stock and no issued or outstanding shares of Series C Preferred
Stock. The rights, privileges and preferences of the Series A, Series B and
Series C Preferred Stock are as stated in the Restated Certificate. At the
first Closing, the Company shall sell at least $1,000,000 of Series C
Preferred. In no event, shall more than 1,183,000 shares of Series C Preferred
be sold pursuant to this Agreement. There can be no assurance that greater than
$1,000,000 of Series C Preferred will be sold pursuant to this Agreement. All
shares sold pursuant to this Agreement shall be sold for $8.65 per share.

                           (b) 20,000,000 shares of Common Stock ("Common
Stock"), of which 2,036,132 shares are issued and outstanding.

                           (c) Except for (i) 1,187,630 shares of Series B
Preferred Stock that may be sold to Rhone-Poulenc Rorer (of which 15% is
subject to purchase directly from the Series A Preferred Stock held by Texas
Biomedical Development Partners) in the event the Company achieves certain
technical milestones, and (ii) 1,250,000 shares of Common Stock reserved for
issuance pursuant to the Company's 1995 Stock Plan (as of the first Closing
442,500 shares are subject to outstanding options and 807,500 shares are
available for future grant), there are no outstanding options, warrants, rights
(including conversion or preemptive rights) or agreements for the purchase or
acquisition from the Company of any shares of its capital stock or any other
securities of the Company.

                           (d) Except as set forth in this Agreement and the
Exhibits hereto, the Company is not a party to or is not subject to any
agreement or understanding relating to, and to the


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<PAGE>   7

Company's knowledge there is no agreement or understanding between any persons
and/or entities which affects or relates to, the voting of shares of capital
stock of the Company or the giving of written consents by a shareholder or
director of the Company.

                  3.3 Subsidiaries. The Company does not presently own or
control, directly or indirectly, any interest in any other corporation,
association, or other business entity.

                  3.4 Authorization. All corporate action on the part of the
Company, its officers, directors and stockholders necessary for the
authorization, execution and delivery of this Agreement, the performance of all
obligations of the Company hereunder and the authorization, issuance (or
reservation for issuance) and delivery of the Series C Preferred sold hereunder
and the Common Stock issuable upon conversion of the Series C Preferred has
been taken or will be taken prior to the Closing. This Agreement constitutes a
valid and legally binding obligation of the Company, enforceable in accordance
with its terms, except as such enforcement is limited by bankruptcy, insolvency
and similar laws affecting creditor rights.

                  3.5 Valid Issuance of Preferred and Common Stock.


                           (a) The Series C Preferred purchased by the
Investors hereunder, when issued, sold and delivered in accordance with the
terms hereof for the consideration expressed herein, will be duly and validly
issued, fully paid and nonassessable and not subject to any preemptive rights,
rights of first refusal or other similar rights imposed by the Company, and
will be issued in compliance with all applicable federal and state securities
laws. The Common Stock issuable upon conversion of the Series C Preferred has
been duly and validly reserved for issuance and, upon issuance in accordance
with the terms of the Restated Certificate, shall be duly and validly issued,
fully paid and nonassessable, free of any liens or encumbrances and not subject
to any preemptive rights, rights of first refusal or other similar rights
imposed by the Company, and issued in compliance with all applicable federal
and state securities laws.

                           (b) The outstanding shares of Common Stock, Series A
Preferred Stock and Series B Preferred Stock are duly and validly authorized
and issued, fully paid and nonassessable, and were issued in compliance with
all applicable federal and state securities laws.

                  3.6 Governmental Consents. No consent, approval, order or
authorization of, or registration, qualification, designation, declaration or
filing with, any federal, state or local governmental authority on the part of
the Company is required in connection with the consummation of the transactions
contemplated by this Agreement, except for registration or qualification, or
taking such action to secure exemption from such registration or qualification,
under applicable state or federal securities laws, which actions shall be taken
on a timely basis as may be required.

                  3.7 Litigation. There is no action, suit, proceeding or
investigation pending or currently threatened against the Company which
questions the validity of this Agreement or the right of the Company to enter
into it, or to consummate the transactions contemplated hereby, or which might
result, either individually or in the aggregate, in any adverse changes in the
assets, condition,


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affairs or prospects of the Company, financially or otherwise, or any change in
the current equity ownership of the Company, nor is the Company aware that
there is any basis for the foregoing. The foregoing includes, without
limitation, actions pending or threatened (on any basis therefor known to the
Company) involving the prior employment of any of the Company's employees,
their use in connection with the Company's business of any information or
techniques allegedly proprietary to any of their former employers, or their
obligations under any agreements with prior employers. The Company is not a
party or subject to the provisions of any order, writ, injunction, judgment or
decree of any court or government agency or instrumentality. There is no
action, suit, proceeding or investigation by the Company currently pending or
which the Company intends to initiate.

                  3.8 Employees. The Company is not aware, nor has a third
party asserted to the Company, that any of its employees is obligated under any
contract (including licenses, covenants or contracts of any nature) or other
agreement, or subject to any judgment, decree or order of any court or
administrative agency, that would interfere with the use of his best efforts to
promote the interests of the Company or that would conflict with the Company's
business as proposed to be conducted. Neither the execution nor delivery of
this Agreement, nor the carrying on of the Company's business by the employees
of the Company, nor the conduct of the Company's business as proposed, will, to
the Company's knowledge, conflict with or result in a breach of the terms,
conditions or provisions of, or constitute a default under, any contract,
covenant or instrument under which any of such employees is now obligated.

                  3.9 Patents and Trademarks. To its knowledge, the Company has
sufficient title and ownership of all trademarks, service marks, trade names,
copyrights, trade secrets, information, proprietary rights, processes, and, to
its knowledge, patents, necessary for its business as now conducted without any
conflict with or infringement of the rights of others. There are no outstanding
options, licenses, or agreements of any kind relating to the foregoing, nor is
the Company bound by or a party to any options, licenses or agreements of any
kind with respect to the patents, trademarks, service marks, trade names,
copyrights, trade secrets, licenses, information, proprietary rights and
processes of any other person or entity. The Company has not received any
communi cations alleging that the Company has violated any of the patents,
trademarks, service marks, trade names, copyrights or trade secrets or other
proprietary rights of any other person or entity.

                  3.10 Compliance with Other Instruments.


                           (a) The Company is not in violation or default of
any provisions of its Certificate of Incorporation or Bylaws or of any
instrument, judgment, order, writ, decree or contract to which it is a party or
by which it is bound or, to its knowledge, of any provision of federal or state
statute, rule or regulation applicable to the Company, and, to its knowledge,
there is no such pro vision which materially and adversely affects the business
of the Company or its properties or assets. The execution, delivery and
performance of this Agreement and the consummation of the transactions
contemplated hereby will not result in any such violation or be in conflict
with or constitute, with or without the passage of time and giving of notice,
either a default under any such provision,


                                      -4-

<PAGE>   9
instrument, judgment, order, writ, decree or contract or an event which results
in the creation of any lien, charge or encumbrance upon any assets of the
Company.

                           (b) The Company has avoided every condition, and has
not performed any act, the occurrence of which would result in the Company's
loss of any right granted under any license, distribution or other agreement.

                  3.11 Adverse Agreements. The Company is not a party to and is
not bound by any contract, agreement or instrument, or subject to any
restriction under its Restated Certificates or Bylaws, which materially
adversely affects its business as now conducted.

                  3.12 Disclosure. The Company has fully provided each Investor
with all the information which such Investor has requested for deciding whether
to purchase the Shares and all information which the Company believes is
reasonably necessary to enable all Investor to make such decision. Neither this
Agreement nor the Confidential Private Placement Memorandum previously provided
to the Investors, when taken as a whole, contains any untrue statement of a
material fact or omits to state a material fact necessary to make the
statements herein or therein not misleading.

                  3.13 Title to Property and Assets. The Company owns its
property and assets free and clear of all mortgages, liens, loans and
encumbrances, except such encumbrances and liens which arise in the ordinary
course of business and do not materially impair the Company's ownership or use
of such property or assets. With respect to the property and assets it leases,
the Company is in compliance with such leases and, to its knowledge, holds a
valid leasehold interest free of any liens, claims or encumbrances.

                  3.14 Financial Statements. The Company has delivered to the
Investors its audited financial statements as of June 30, 1995 and June 30,
1994, and for the period from the Company's inception through June 30, 1995
(the "Financial Statements"). The Financial Statements have been prepared in
accordance with generally accepted accounting principles applied on a
consistent basis throughout the periods indicated and with each other and
includes all footnotes required by generally accepted accounting principles.
The Financial Statements fairly present the financial condition and operating
results of the Company as of the dates, and for the periods, indicated therein.
Except as set forth in the Financial Statements, the Company has no material
liabilities, contingent or otherwise, other than (i) liabilities incurred in
the ordinary course of business subsequent to June 30, 1995 and (ii)
obligations under contracts and commitments incurred in the ordinary course of
business and not required under generally accepted accounting principles to be
reflected in the Financial Statements, which, in both cases, individually or in
the aggregate, are not material to the financial condition or operating results
of the Company. Except as disclosed in the Financial Statements, the Company is
not a guarantor or indemnitor of any indebtedness of any other person, firm or
corporation. The Company maintains and will continue to maintain a standard
system of accounting established and administered in accordance with generally
accepted accounting principles.



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<PAGE>   10

                  3.15 Employee Benefit Plans. Other than the Company's 401(k)
plan (to which the Company is not obligated to make contributions), the Company
does not have any Employee Benefit Plan as defined in the Employee Retirement
Income Security Act of 1974.

                  3.16 Tax Returns, Payments and Elections. The Company has
filed all tax returns and reports as required by law. These returns and reports
are true and correct in all material respects. The Company has not elected
pursuant to the Internal Revenue Code of 1986, as amended ("Code"), to be
treated as a Subchapter S corporation or a collapsible corporation pursuant to
Section 341(f) or Section 1362(a) of the Code, nor has it made any other
elections pursuant to the Code (other than elections which relate solely to
methods of accounting, depreciation or amortization) which would have a
material effect on the Company, its financial condition, its business as
presently conducted or proposed to be conducted or any of its properties or
material assets.

                  3.17 Labor Agreements and Actions. The Company is not bound
by or subject to (and none of its assets or properties is bound by or subject
to) any written or oral, express or implied, contract, commitment or
arrangement with any labor union, and no labor union has requested or, to the
knowledge of the Company, has sought to represent any of the employees,
representatives or agents of the Company. There is no strike or other labor
dispute involving the Company pending, or to the knowledge of the Company
threatened, which could have a material adverse effect on the assets,
properties, financial condition, operating results, or business of the Company
(as such business is presently conducted and as it is proposed to be
conducted), nor is the Company aware of any labor organization activity
involving its employees. The Company is not aware that any officer or key
employee, or that any group of key employees, intends to terminate their
employment with the Company, nor does the Company have a present intention to
terminate the employment of any of the foregoing. The employment of each
officer and employee of the Company is terminable at the will of the Company.

                  3.18 Offering. Subject in part on the accuracy of the
Investors' representations set forth in Section 4 of this Agreement, the offer,
sale and issuance of the Shares to be issued in conformity with the terms of
this Agreement constitute transactions exempt from the registration
requirements of Section 5 of the Securities Act of 1933, as amended (the
"Act"), and from all applicable state registration or qualification
requirements.

         4.       Representations and Warranties of the Investors. Each
Investor hereby represents and warrants the following:

                  4.1 Authorization. This Agreement constitutes its valid and
legally binding obligation, enforceable in accordance with its terms, except as
such enforcement is limited by bankruptcy, insolvency and similar laws affecting
creditor rights. It has full power and authority to enter into this Agreement.

                  4.2 Purchase Entirely for Own Account. This Agreement is made
with the Investors in reliance upon the Investors' representation to the
Company, which each Investor



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<PAGE>   11

execution of this Agreement hereby confirms, that the Series C Preferred to be
received by the Investor and the Common Stock issuable upon conversion of the
Series C Preferred Stock (collectively, the "Securities") will be acquired for
investment for the Investor's own account, not as a nominee or agent, and not
with a view to the resale or distribution of any part thereof, and that the
Investor has no present intention of selling, granting any participation in, or
otherwise distributing the same. By executing this Agreement, the Investor
further represents that the Investor does not have any contract, undertaking,
agreement or arrangement with any person to sell, transfer or grant
participation to such person or to any third person, with respect to any of the
Securities.

                  4.3 Disclosure of Information. The Investor has received all
the information it considers necessary or appropriate for deciding whether to
purchase the Series C Preferred hereunder. The Investor further represents that
it has had an opportunity to ask questions and receive answers from the Company
regarding the terms and conditions of the offering of the Series C Preferred.

                  4.4 Investment Experience. The Investor is an investor in
securities of companies in the development stage and acknowledges it is able to
fend for itself, and bear the economic risk of its investment and has such
knowledge and experience in financial or business matters that it is capable of
evaluating the merits and risks of the investment in the Series C Preferred
hereunder.

                  4.5 Accredited Investor. It is an "accredited investor" as
defined in Rule 501(a) promulgated under the Securities Act.

                  4.6 Residence. The legal residence of the Investor is set
forth on its signature page to this Agreement.

                  4.7 Restricted Securities. The Investor understands that the
shares of Series C Preferred it is purchasing are characterized as "restricted
securities" under the federal securities laws inasmuch as they are being
acquired from the Company in a transaction not involving a public offering and
that under such laws and applicable regulations such securities may be resold
without registration under the Act only in certain limited circumstances. In
this connection, the Investor represents that it is familiar with Rule 144, as
presently in effect, and understands the resale limitations imposed thereby and
by the Act. The Investor understands that there is no public market for the
Securities and there can be no assurance that there will ever be a public
market for the Securities.

                  4.8 Further Limitations on Disposition. Without in any way
limiting the representations set forth above, the Investor further agrees not
to make any disposition of all or any portion of the Series C Preferred
purchased hereunder or Common Stock issuable upon the conversion of the Series
C Preferred, unless and until:



                                      -7-
<PAGE>   12

                           (a) There is then in effect a Registration Statement
under the Act covering such proposed disposition and such disposition is made
in accordance with such Registration Statement; or

                           (b) (i) The Investor shall have notified the Company
of the proposed disposition and shall have furnished the Company with a
detailed statement of the circumstances surrounding the proposed disposition,
and (ii) if reasonably requested by the Company, the Investor shall have
furnished the Company with an opinion of counsel, reasonably satisfactory to
the Company, that such disposition will not require registration of such shares
under the Act.

                           (c) Notwithstanding the provisions of paragraphs (a)
and (b) above, no such registration statement or opinion of counsel shall be
necessary for a transfer by an Investor pursuant to Rule 144 if such Investors
makes the factual representations reasonably requested by the Company
indicating the availability of the exemption provided by Rule 144.

                  4.9 Legends. It is understood that the certificates
evidencing the Series C Preferred and the Common Stock issuable upon conversion
thereof, may bear one or all of the following legends:

                           (a) "THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR
HYPOTHECATED IN THE ABSENCE OF A REGISTRATION STATEMENT IN EFFECT WITH RESPECT
TO THE SECURITIES UNDER SUCH ACT OR AN OPINION OF COUNSEL SATISFACTORY TO THE
COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE SECURITIES ACT OF
1933."

                           (b) Any legend required by applicable state
securities laws.

         5.       Conditions to Closing of Investors. The Investors' obligation
to purchase the Series C Preferred at a Closing is, at the option of each
Investor, subject to the fulfillment as of the Closing Date of the following
conditions:

                  5.1 Representations and Warranties Correct. The
representations and warranties made by the Company in Section 3 hereof shall be
true and correct in all material respects as of the Closing Date.

                  5.2 Covenants. All covenants, agreements and conditions
contained in this Agreement to be performed by the Company on or prior to the
Closing Date shall have been performed or complied with in all material
respects.

                  5.3 Blue Sky. The Company shall have obtained all necessary
Blue Sky law permits and qualifications, or have the availability of exemptions
therefrom, required by any state for the offer and sale of the Series C
Preferred and the Common Stock issuable upon conversion thereof.


                                      -8-
<PAGE>   13

                  5.4 Restated Certificate. The Restated Certificate shall have
been filed with the Delaware Secretary of State.

                  5.5 Minimum Purchase Amount. The first Closing under this
Agreement shall be for at least $1,000,000 of Series C Preferred Stock.

         6. Conditions to Closing of Company. The Company's obligation to sell
and issue the Series C Preferred at a Closing is, at the option of the Company,
subject to the fulfillment as of the Closing Date of the following conditions:

                  6.1 Representations. The representations made by the
Investors in Section 4 hereof shall be true and correct when made, and shall be
true and correct in all material respects on the Closing Date.

                  6.2 Blue Sky. The Company shall have obtained all necessary
Blue Sky law permits and qualifications, or have the availability of exemptions
therefrom, required by any state for the offer and sale of the Series C
Preferred and the Common Stock issuable upon conversion thereof.

                  6.3 Restated Certificate. The Restated Certificate shall have
         been filed with the Delaware Secretary of State.

         7.       Registration Rights. The Company covenants and agrees as
follows:

                  7.1 Definitions. For purposes of this Section 7:


                           (a) The term "register," "registered," and
"registration" refer to a registration effected by preparing and filing a
registration statement or similar document in compliance with the Act, and the
declaration or ordering of effectiveness of such registration statement or
document;

                           (b) The term "Registrable Securities" means (1) the
Common Stock issuable or issued upon conversion of the Company's Series B
Preferred Stock, (2) the Common Stock issuable or issued upon conversion of any
Series A Preferred Stock held by individuals and entities who signed a consent
for the purpose of being bound by Section 20 of the Company's Series B
Preferred Stock Purchase Agreement, (3) any Common Stock held by individuals
and entities who have signed a consent for the purposes of being bound by
Section 20 of the Company's Series B Preferred Stock Purchase Agreement; (4)
the Common Stock issuable or issued upon conversion of the Company's Series C
Preferred Stock and (5) any Common Stock of the Company issued as (or issuable
upon the conversion or exercise of any warrant, right or other security which
is issued as) a dividend or other distribution with respect to, or in exchange
for or in replacement of, such Series A Preferred Stock, Series B Preferred
Stock, Series C Preferred Stock, or Common Stock, excluding in all cases,
however, (i) any Registrable Securities sold by a person in a transaction in
which his rights


                                      -9-
<PAGE>   14

under this Section 7 are not assigned, or (ii) any Registrable Securities sold
to or through a broker or dealer or underwriter in a public distribution or a
public securities transaction.

                           (c) The number of shares of "Registrable Securities
then outstanding" shall be determined by the number of shares of Common Stock
outstanding which are, and the number of shares of Common Stock issuable
pursuant to then exercisable or convertible securities which are, Registrable
Securities.

                           (d) The term "Holder" means any person owning or
having the right to acquire Registrable Securities or any assignee thereof in
accordance with Section 7.13 hereof; and

                           (e) The term "Form S-3" means such form under the
Act as in effect on the date hereof or any registration form under the Act
subsequently adopted by the Securities and Exchange Commission ("SEC") which
permits inclusion or incorporation of substantial information by reference to
other documents filed by the Company with the SEC.

                           (f) The term "Act" shall mean the Securities Act of
1933, as amended.

                  7.2 Request for Registration.


                           (a) If the Company shall receive at any time after
December 31, 1998, either (i) a written request from the Holders of at least
fifty percent (50%) of the Registrable Securities (including securities
convertible into Registrable Securities) then outstanding that the Company file
a registration statement under the Act covering the registration of at least
forty percent (40%) of the Registrable Securities (or a lesser percentage if
the anticipated aggregate offering price, net of underwriting discounts and
commissions, would exceed $10,000,000) or (ii) a written request from
Rhone-Poulenc Rorer Pharmaceuticals, Inc. that the Company file a registration
statement under the Act covering the registration of at least sixty percent
(60%) of the Registrable Securities held by Rhone-Poulenc Rorer
Pharmaceuticals, Inc. (or a lesser percentage if the anticipated aggregate
offering price, net of underwriting discounts and commissions would exceed
$10,000,000), then the Company shall, within ten (10) days of the receipt
thereof, give written notice of such request to all Holders and shall, subject
to the limitations of subsections 7.2(b) and (c), effect as soon as
practicable, and in any event within 120 days of the receipt of such request,
the registration under the Act of all Registrable Securities which the Holders
request to be registered within 20 days of the mailing of such written notice
by the Company.

                           (b) Notwithstanding the foregoing, the Company shall
not be obligated to take any action to effect any such registration,
qualification or compliance pursuant to subsection 7.2(a):

                                    (i) During the period starting with the
date sixty (60) days prior to the Company's estimated date of filing of, and
ending on the date six months immediately following the effective date of, any
registration statement pertaining to securities of the Company (other than a
registration of securities in a Rule 145 transaction or with respect to an
employee benefit plan),


                                     -10-
<PAGE>   15

provided that the Company is actively employing in good faith all reasonable
efforts to cause such registration statement to become effective;

                                    (ii) After the Company has effected two
registrations pursuant to subsection 7.2(a) (i) (if the request is being made
pursuant to subsection 7.2(a)(i)), and such registration has been declared or
ordered effective, or after the Company has effected a single registration
pursuant to subsection 7.2(a)(ii) (if the request is being made pursuant to
subsection 7.2(a)(ii)) and such registration has been declared or ordered
effective;

                                    (iii) If the Company shall furnish to such
Holders a certificate signed by the President of the Company stating that in
the good faith judgment of the Board of Directors it would be seriously
detrimental to the Company or its shareholders for a registration statement to
be filed at such time, then the Company's obligation to use its best efforts to
register, qualify or comply under subsection 7.2(a) shall be deferred for a
period not to exceed 120 days from the date of receipt of written request from
the Holders; provided, however, that the Company may not utilize this right
more than once in any twelve-month period.

                           (c) If the Holders initiating the registration
request hereunder ("Initiating Holders") intend to distribute the Registrable
Securities covered by their request by means of an underwriting, they shall so
advise the Company as a part of their request made pursuant to this Section 7.2
and the Company shall include such information in the written notice referred
to in subsection 7.2(a). In such event, the right of any Holder to include his
Registrable Securities in such registration shall be conditioned upon such
Holder's participation in such underwriting and the inclusion of such Holder's
Registrable Securities in the underwriting (unless otherwise mutually agreed by
a majority in interest of the Holders requesting the registration and such
Holder) to the extent provided herein. All Holders proposing to distribute
their securities through such underwriting shall (together with the Company as
provided in subsection 7.4(e)) enter into an underwriting agreement in
customary form with the underwriter or underwriters selected for such
underwriting by a majority in interest of the Holders requesting the
registration and reasonably acceptable to the Company. Notwithstanding any
other provision of this Section 7.2, if the underwriter advises the Holders
requesting the registration that marketing factors require a limitation of the
number of shares to be underwritten, then the Initiating Holders shall so
advise all Holders of Registrable Securities which would otherwise be
underwritten pursuant hereto, and the number of shares of Registrable
Securities that may be included in the underwriting shall be allocated among
all Holders thereof, in proportion (as nearly as practicable) to the amount of
Registrable Securities of the Company owned by each Holder; provided, however,
that the number of shares of Registrable Securities to be included in such
underwriting shall not be reduced unless all other securities are first
entirely excluded from such underwriting.

                  7.3 Company Registration. If (but without any obligation to
do so) the Company proposes to register (including for this purpose a
registration effected by the Company for shareholders other than the Holders)
any of its stock or other securities under the Act in connection with the
public offering of such securities solely for cash (other than a registration
relating solely to the sale of securities to participants in a Company stock
plan, or a registration on any form which


                                     -11-
<PAGE>   16

does not include substantially the same information as would be required to be
included in a registration statement covering the sale of the Registrable
Securities), the Company shall, at such time, promptly give each Holder written
notice of such registration. Upon the written request of each Holder given
within twenty (20) days after mailing of written notice by the Company, the
Company shall, subject to the provisions of Section 7.8, cause to be registered
under the Act all of the Registrable Securities that each such Holder has
requested to be registered.

                  7.4 Obligations of the Company. Whenever required under this
Section 7 to effect the registration of any Registrable Securities, the Company
shall, as expeditiously as reasonably possible:

                           (a) Prepare and file with the SEC a registration
statement with respect to such Registrable Securities and use its best efforts
to cause such registration statement to become effective, and, upon the request
of the Holders of a majority of the Registrable Securities registered
thereunder, keep such registration statement effective for up to sixty (60)
days.

                           (b) Prepare and file with the SEC such amendments
and supplements to such registration statement and the prospectus used in
connection with such registration statement as may be necessary to comply with
the provisions of the Act with respect to the disposition of all securities
covered by such registration statement.

                           (c) Furnish to the Holders such numbers of copies of
a prospectus, including a preliminary prospectus, in conformity with the
requirements of the Act, and such other documents as they may reasonably
request in order to facilitate the disposition of Registrable Securities owned
by them.

                           (d) Use its best efforts to register and qualify the
securities covered by such registration statement under such other securities
or Blue Sky laws of such jurisdictions as shall be reasonably requested by the
Holders, provided that the Company shall not be required in connection
therewith or as a condition thereto to qualify to do business or to file a
general consent to service of process in any such states or jurisdictions.

                           (e) In the event of any underwritten public
offering, enter into and perform its obligations under an underwriting
agreement, in usual and customary form, with the managing underwriter of such
offering. Each Holder participating in such underwriting shall also enter into
and perform its obligations under such an agreement.

                           (f) Notify each Holder of Registrable Securities
covered by such registration statement at any time when a prospectus relating
thereto is required to be delivered under the Act of the happening of any event
as a result of which the prospectus included in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading in the light of the circumstances then
existing.


                                     -12-
<PAGE>   17

                           (g) Furnish, at the request of any Holder requesting
registration of Registrable Securities pursuant to this Section 7, on the date
that such Registrable Securities are delivered to the underwriters for sale in
connection with a registration pursuant to this Section 7, if such securities
are being sold through underwriters, or, if such securities are not being sold
through underwriters, on the date that the registration statement with respect
to such securities becomes effective, (i) an opinion, dated such date, of the
counsel representing the Company for the purposes of such registration, in form
and substance as is customarily given to underwriters in an underwritten public
offering, addressed to the underwriters, if any, and to the Holders requesting
registration of Registrable Securities and (ii) a letter dated such date, from
the independent certified public accountants of the Company, in form and
substance as is customarily given by independent certified public accountants
to underwriters in an underwritten public offering, addressed to the
underwriters, if any, and to the Holders requesting registration of Registrable
Securities.

                  7.5 Furnish Information. It shall be a condition precedent to
the obligations of the Company to take any action pursuant to this Section 7
with respect to the Registrable Securities of any selling Holder that such
holder shall furnish to the Company such information regarding itself, the
Registrable Securities held by it, and the intended method of disposition of
such securities as shall be required to effect the registration of such
Holder's Registrable Securities.

                  7.6 Expenses of Demand Registration. All expenses, other than
underwriting discounts and commissions and any fees and expenses of a special
counsel of a selling stockholder, incurred in connection with registrations,
filings or qualifications pursuant to Section 7.2, including (without
limitation) all registration, federal and state filing and qualification fees
and expenses, printers' and accounting fees and fees and disbursements of
counsel for the Company, shall be paid by the Company; provided, however, that
the Company shall not be required to pay for any expenses of any registration
proceeding begun pursuant to Section 7.2 if the registration request is
subsequently withdrawn at the request of the Holders of a majority of the
Registrable Securities to be registered (in which case all Participating
Holders shall bear such expenses), unless the Holders of a majority of the
Registrable Securities agree to forfeit their right to one demand registration
pursuant to Section 7.2; provided further, however, that if at the time of such
withdrawal, the Holders have learned of a material adverse change in the
condition, business, or prospects of the Company from that known to the Holders
at the time of their request, then the Holders shall not be required to pay any
of such expenses and shall retain their rights pursuant to Section 7.2. The
Company's obligations under this 7.6 shall apply to each registration pursuant
to Section 7.2.

                  7.7 Expenses of Company Registration. The Company shall bear
and pay all expenses incurred in connection with any registration, filing or
qualification of Registrable Securities with respect to the registrations
pursuant to Section 7.3 for each Holder (which right may be assigned as
provided in Section 7.13), including (without limitation) all registration,
filing, qualification, printers and accounting fees relating or apportionable
thereto, but excluding underwriting discounts and commissions relating to
Registrable Securities and any fees or expenses of a special counsel of a
selling stockholder.


                                     -13-
<PAGE>   18

                  7.8 Underwriting Requirements. In connection with any
offering involving an underwriting of shares being issued by the Company, the
Company shall not be required under Section 7.3 to include any of the Holders'
securities in such underwriting unless they accept the terms of the
underwriting as agreed upon between the Company and the underwriters selected
by it, and then only in such quantity as is provided for herein. If the
underwriters determine that marketing factors require a limitation of the
number of shares to be underwritten, the underwriters may limit the number of
Registrable Securities to be included in the registration on a pro-rata basis,
or may exclude Registrable Securities entirely from such registration (the
securities so included to be apportioned pro rata among the selling
stockholders according to the total amount of securities entitled to be
included therein owned by each selling stockholder or in such other proportions
as shall mutually be agreed to by such selling stockholders) but in no event
shall any shares being sold by a stockholder exercising a demand registration
right similar to that granted in Section 7.2 be excluded from such offering.
For purposes of apportionment, any selling stockholder which is a Holder of
Registrable Securities and which is a partnership or corporation, the partners,
retired partners and shareholders of such Holder, or the estates and family
members of any such partners and retired partners and any trusts for the
benefit of any of the foregoing persons shall be deemed to be a single "selling
stockholder", and any pro rata reduction with respect to such "selling
stockholder" shall be based upon the aggregate amount of shares carrying
registration rights owned by all entities and individuals included in such
"selling stockholder", as defined in this sentence.

                  7.9 Delay of Registration. No Holder shall have any right to
obtain or seek an injunction restraining or otherwise delaying any such
registration as the result of any controversy that might arise with respect to
the interpretation or implementation of this Section 7.

                  7.10 Indemnification. In the event any Registrable Securities
are included in a registration statement under this Section 7:

                           (a) To the extent permitted by law, the Company will
indemnify and hold harmless each Holder, any underwriter (as defined in the
Act) for such Holder and each person, if any, who controls such Holder or
underwriter within the meaning of the Act or the Securities Exchange Act of
1934, amended (the "1934 Act"), against any losses, claims, damages, or
liabilities (joint or several) to which they may become subject under the Act,
the 1934 Act or other federal or state law, insofar as such losses, claims,
damages, or liabilities (or actions in respect thereof) arise out of or are
based upon any of the following statements, omissions or violations
(collectively a "Violation"): (i) any untrue statement or alleged untrue
statement of a material fact contained in such registration statement,
including any preliminary prospectus or final prospectus contained therein or
any amendments or supplements thereto, (ii) the omission or alleged omission to
state therein a material fact required to be stated therein, or necessary to
make the statements therein not misleading, or (iii) any violation or alleged
violation by the Company of the Act, the 1934 Act, any state securities law or
any rule or regulation promulgated under the Act, the 1934 Act or any state
securities law; and the Company will pay to each such Holder, underwriter or
controlling person, as incurred, any legal or other expenses reasonably
incurred by them in connection with investigating or defending any such loss,
claim, damage, liability, or action; provided, however, that the indemnity
agreement contained in this subsection 7.10(a) shall not apply to amounts paid
in settlement of any


                                     -14-
<PAGE>   19

such loss, claim, damage, liability, or action if such settlement is effected
without the consent of the Company (which consent shall not be unreasonably
withheld), nor shall the Company be liable in any such case for any such loss,
claim, damage, liability, or action to the extent that it arises out of or is
based upon a Violation which occurs in reliance upon and in conformity with
written information furnished expressly for use in connection with such
registration by any such Holder, underwriter or controlling person.

                           (b) To the extent permitted by law, each selling
Holder will indemnify and hold harmless the Company, each of its directors,
each of its officers who has signed the registration statement, each person, if
any, who controls the Company within the meaning of the Act, any underwriter,
any other Holder selling securities in such registration statement and any
controlling person of any such underwriter or other Holder, against any losses,
claims, damages, or liabilities (joint or several) to which any of the
foregoing persons may become subject, under the Act, the 1934 Act or other
federal or state law, insofar as such losses, claims, damages, or liabilities
(or actions in respect thereto) arise out of or are based upon any Violation,
in each case to the extent (and only to the extent) that such Violation occurs
in reliance upon and in conformity with written information furnished by such
Holder expressly for use in connection with such registration; and each such
Holder will pay, as incurred, any legal or other expenses reasonably incurred
by any person intended to be indemnified pursuant to this subsection 7.10(b),
in connection with investigating or defending any such loss, claim, damage,
liability, or action; provided, however, that the indemnity agreement contained
in this subsection 7.10(b) shall not apply to amounts paid in settlement of any
such loss, claim, damage, liability or action if such settlement is effected
without the consent of the Holder, which consent shall not be unreasonably
withheld; provided, that, in no event shall any indemnity under this subsection
7.10(b) exceed the gross proceeds from the offering received by such Holder.

                           (c) Promptly after receipt by an indemnified party
under this Section 7.10 of notice of the commencement of any action (including
any governmental action), such indemnified party will, if a claim in respect
thereof is to be made against any indemnifying party under this Section 7.10,
deliver to the indemnifying party a written notice of the commencement thereof
and the indemnifying party shall have the right to participate in, and, to the
extent the indemnifying party so desires, jointly with any other indemnifying
party similarly noticed, to assume the defense thereof with counsel mutually
satisfactory to the parties; provided, however, that an indemnified party shall
have the right to retain its own counsel, with the fees and expenses to be paid
by the indemnifying party, if representation of such indemnified party by the
counsel retained by the indemnifying party would be inappropriate due to actual
or potential differing interests between such indemnified party and any other
party represented by such counsel in such proceeding. The failure to deliver
written notice to the indemnifying party within a reasonable time of the
commencement of any such action, if prejudicial to its ability to defend such
action, shall relieve such indemnifying party of any liability to the
indemnified party under this Section 7.10, but the omission so to deliver
written notice to the indemnifying party will not relieve it of any liability
that it may have to any indemnified party otherwise than under this Section
7.10.


                                     -15-
<PAGE>   20

                           (d) The obligations of the Company and Holders under
this Section 7.10 shall survive the completion of any offering of Registrable
Securities in a registration statement under this Section 7, and otherwise.

                  7.11 Reports Under Securities Exchange Act of 1934. With a
view to making available to the Holders the benefits of Rule 144 promulgated
under the Act and any other rule or regulation of the SEC that may at any time
permit a Holder to sell securities of the Company to the public without
registration or pursuant to a registration on Form S-3, the Company agrees to:

                           (a) make and keep public information available, as
those terms are understood and defined in SEC Rule 144, at all times after
ninety (90) days after the effective date of the first registration statement
filed by the Company for the offering of its securities to the general public;

                           (b) take such action, including the voluntary
registration of its Common Stock under Section 12 of the 1934 Act, as is
necessary to enable the Holders to utilize Form S-3 for the sale of their
Registrable Securities, such action to be taken as soon as practicable after
the end of the fiscal year in which the first registration statement filed by
the Company for the offering of its securities to the general public is
declared effective;

                           (c) file with the SEC in a timely manner all reports
and other documents required of the Company under the Act and the 1934 Act; and

                           (d) furnish to any Holder, so long as the Holder
owns any Registrable Securities, forthwith upon request (i) a written statement
by the Company that it has complied with the reporting requirements of SEC Rule
144 (at any time after ninety (90) days after the effective date of the first
registration statement filed by the Company), the Act and the 1934 Act (at any
time after it has become subject to such reporting requirements), or that it
qualifies as a registrant whose securities may be resold pursuant to Form S-3
(at any time after it so qualifies), (ii) a copy of the most recent annual or
quarterly report of the Company and such other reports and documents so filed
by the Company, and (iii) such other information as may be reasonably requested
in availing any Holder of any rule or regulation of the SEC (exclusive of Rule
144A) which permits the selling of any such securities without registration or
pursuant to such form.

                  7.12 Form S-3 Registration. In case the Company shall receive
from any Holder or Holders of the Registrable Securities a written request or
requests that the Company effect a registration on Form S-3 and any related
qualification or compliance with respect to shares of Registrable Securities
the reasonably anticipated aggregate price to the public of which, net of
underwriting discounts and commissions, would exceed $1,000,000 all or a part
of the Registrable Securities owned by such Holder or Holders, the Company
will:

                           (a) promptly give written notice of the proposed
registration, and any related qualification or compliance, to all other
Holders; and


                                     -16-
<PAGE>   21

                           (b) as soon as practicable, effect such registration
and all such qualifications and compliances as may be so requested and as would
permit or facilitate the sale and distribution of all or such portion of such
Holder's or Holders' Registrable Securities as are specified in such request,
together with all or such portion of the Registrable Securities of any other
Holder or Holders joining in such request as are specified in a written request
given within 15 days after receipt of such written notice from the Company;
provided, however, that the Company shall not be obligated to effect any such
registration, qualification or compliance, pursuant to this Section 7.12: (1)
if Form S-3 is not available for such offering by the Holders; (2) if the
Holders, together with the holders of any other securities of the Company
entitled to inclusion in such registration, propose to sell Registrable
Securities and such other securities (if any) at an aggregate price to the
public (net of any underwriters' discounts or commissions) of less than
$1,000,000; (3) if the Company shall furnish to the Holders a certificate
signed by the President of the Company stating that in the good faith judgment
of the Board of Directors of the Company, it would be seriously detrimental to
the Company and its shareholders for such Form S-3 Registration to be effected
at such time, in which event the Company shall have the right to defer the
filing of the Form S-3 registration statement for a period of not more than 120
days after receipt of the request of the Holder or Holders under this Section
7.12; provided, however, that the Company shall not utilize this right more
than once in any twelve (12) month period; or (4) in any particular
jurisdiction in which the Company would be required to qualify to do business
or to execute a general consent to service of process in effecting such
registration, qualification or compliance.

                           (c) Subject to the foregoing, the Company shall file
a registration statement covering the Registrable Securities and other
securities so requested to be registered as soon as practicable after receipt
of the request or requests of the Holders. All expenses incurred in connection
with the registrations requested pursuant to Section 7.12, (exclusive of
underwriting discounts and commissions and any fees and expenses of a special
counsel to a selling shareholder) shall be paid by the Company.

                  7.13 Assignment of Registration Rights. The rights to cause
the Company to register Registrable Securities pursuant to this Section 7 may
be assigned by a Holder to a transferee or assignee of such securities who
acquires (i) at least 300,000 shares of Registrable Securities, or (ii) all
shares of Registrable Securities then held by such Holder if such Holder
transfers all such Registrable Securities to a single entity, provided the
Company is, within a reasonable time after such transfer, furnished with
written notice of the name and the address of such transferee or assignee and
the securities with respect to which such registration rights are being
assigned; and provided, further, that such assignment shall be effective only
if immediately following such transfer the further disposition of such
securities by the transferee or assignee is restricted under the Act.
Notwithstanding the above, such rights may be assigned by a Holder to a limited
partner or general partner of the Holder regardless of the number of shares
acquired by such transferee.

                  7.14 Limitations on Subsequent Registration Rights. From and
after the date of this Agreement, the Company shall not, without the prior
written consent of the Holders of a majority of the Registrable Securities,
enter into any agreement (other than an amendment to this agreement or
supplemental agreement effected in accordance with Section 7.16 of this
Agreement)


                                     -17-
<PAGE>   22

with any holder or prospective holder of any securities of the Company which
would allow such holder or prospective holder (a) to include such securities in
any registration filed pursuant to Section 7.2 hereof, unless under the terms
of such agreement such holder or prospective holder may include such securities
in any such registration only to the extent that the inclusion of such
securities will not reduce the amount of the Registrable Securities of the
Holders which are included in any such registration or (b) to make a demand
registration which could result in such registration being declared effective
prior to the earlier of either of the dates set forth in subsection 7.2(a) or
within six months of the effective date of any registration effected pursuant
to Section 7.2.

                  7.15 "Market Stand-Off" Agreement. Each holder of securities
which are or at one time were Registrable Securities (or which are or were
convertible into Registrable Securities) hereby agrees that, during a period
not to exceed 180 days, following the effective date of a registration
statement of the Company filed under the Act, it shall not, to the extent
requested by the Company and such underwriter, sell or otherwise transfer or
dispose of (other than to donees who agree to be similarly bound) any Common
Stock or Preferred Stock of the Company held by it at any time during such
period except Common Stock included in such registration; provided, however,
that:

                           (a) such agreement shall be applicable only to the
first such registration statement of the Company which covers Common Stock (or
other securities) to be sold on its behalf to the public in an underwritten
offering; and

                           (b) all officers and directors of the Company, and
all other persons with registration rights (whether or not pursuant to this
Agreement) enter into similar agreements.

                  In order to enforce the foregoing covenant, the Company may
impose stop-transfer instructions with respect to the Registrable Securities of
each Holder (and the shares or securities of every other person subject to the
foregoing restriction) until the end of such period.

                  7.16 Amendment of Registration Rights. Any provision of this
Section 7 may be amended and the observance thereof may be waived (either
generally or in a particular instance and either retroactively or
prospectively), only with the written consent of (i) the Company, (ii) the
holders of at least sixty-seven percent (67%) of the Registrable Securities
then outstanding, (iii) the holders of a majority of the Series B Preferred
Stock then outstanding and (iv) the holders of a majority of the Series C
Preferred Stock then outstanding, and with the same consent the Company may
enter into a supplemental agreement for the purpose of adding any provisions to
or changing in any manner or eliminating any of the provisions of this Section
7. Any amendment, waiver or supplemental agreement effected in accordance with
this Section 7.16 shall be binding upon each holder of any securities which are
or at one time were Registrable Securities (or which are or were convertible
into Registrable Securities), each future holder of all such securities, and
the Company.


                                     -18-
<PAGE>   23

                  7.17 Termination of Registration Rights. No stockholder shall
be entitled to exercise any right provided for in this Section 7 after six (6)
years following the consummation of the sale of securities pursuant to a
registration statement filed by the Company under the Act in connection with
the initial underwritten offering of its securities to the general public.

                  7.18 Prior Registration Rights. Each undersigned Investor and
each undersigned party who joins this Agreement solely for the purposes of this
Section 7 who is entitled to registration rights pursuant to the Company's
Series B Preferred Stock Purchase Agreement hereby agrees on behalf of all
holders of such registration rights that they shall be amended and restated in
their entirety and the registration rights under this Section 7 shall be
substituted.

          8.      Miscellaneous.

                  8.1 Survival of Warranties. The warranties, representations
and covenants of the Company and the Investors contained in this Agreement
shall survive the execution and delivery of this Agreement and the Closing and
shall in no way be affected by any investigation of the subject matter thereof
made by or on behalf of the Investors or the Company.

                  8.2 Successors and Assigns. The terms and conditions of this
Agreement shall inure to the benefit of and be binding upon the respective
successors and assigns of the parties. Nothing in this Agreement, express or
implied, is intended to confer upon any party other than the parties hereto or
their respective successors and assigns any rights, remedies, obligations, or
liabilities under or by reason of this Agreement, except as expressly provided
in this Agreement.

                  8.3 Governing Law. This Agreement shall be governed by and
construed under the laws of the State of Delaware as applied to agreements
among Delaware residents entered into and to be performed entirely within
Delaware.

                  8.4 Counterparts. This Agreement may be executed in two or
more counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

                  8.5 Titles and Subtitles. The titles and subtitles used in
this Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

                  8.6 Notices. Unless otherwise provided, any notice required
or permitted under this Agreement shall be given in writing and shall be deemed
effectively given upon personal delivery to the party to be notified or upon
deposit with the United States Post Office, by registered or certified mail, or
other courier service, postage prepaid and addressed to the party to be
notified at the address indicated for such party in the Company's stock records
or in the case of the Company on the first page of this Agreement, or at such
other address as such party may designate by ten (10) days' advance written
notice to the other parties.


                                     -19-
<PAGE>   24

                  8.7 Expenses. Each party shall pay its own fees and expenses
with respect to this Agreement. If any action at law or in equity is necessary
to enforce or interpret the terms of this Agreement or the Restated Articles,
the prevailing party shall be entitled to reasonable attorney's fees, costs and
necessary disbursements in addition to any other relief to which such party may
be entitled.

                  8.8 Amendments and Waivers. Any term of this Agreement may be
amended and the observance of any term of this Agreement may be waived (either
generally or in a particular instance and either retroactively or
prospectively), only with the written consent of the Company and the Investors.

                  8.9 Severability. If one or more provisions of this Agreement
are held to be unenforceable under applicable law, such provision shall be
excluded from this Agreement and the balance of the Agreement shall be
interpreted as if such provision were so excluded and shall be enforceable in
accordance with its terms.

                  8.10 Aggregation of Stock. All shares of Common Stock, Series
A Preferred Stock, Series B Preferred and Series C Preferred Stock held or
acquired by affiliated entities or persons shall be aggregated together for the
purpose of determining the availability of any rights under this Agreement.


                                      -20-

<PAGE>   25

          IN WITNESS WHEREOF, the parties have executed this Series C Preferred
Stock Purchase Agreement as of the date set forth below.

                                        INTROGEN THERAPEUTICS, INC.


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


                                        INVESTOR:


                                        ----------------------------------
                                        (print name)

                                        ----------------------------------
                                        (signature)

                                        ----------------------------------
                                        (title, if applicable)

                      Resident Address:
                                        ----------------------------------

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

                                        ----------------------------------
                      Number of
                      Shares Purchased:
                                        ----------------------
                      Date:
                                        ----------------------


                                     -21-
<PAGE>   26

                                   EXHIBIT A

                                   [omitted]