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                                                                  EXHIBIT 10.46

EXECUTION COPY



                          ARONEX PHARMACEUTICALS, INC.

                           PLACEMENT AGENCY AGREEMENT



                                                  Dated as of November 19, 1998

Paramount Capital, Inc.
787 Seventh Avenue, 48th Floor
New York, New York  10019

Dear Sirs:

                  Aronex Pharmaceuticals, Inc., a Delaware corporation (the
"Company") proposes to issue, offer and sell (the "Offering"), up to an
aggregate of 6,000,000 shares (the "Shares") of its common stock (the "Offering
Amount"), par value $.001 per share (the "Common Stock"). The Company hereby
confirms its agreement to retain Paramount Capital, Inc. (the "Placement
Agent") on an exclusive "best efforts" basis to introduce the Company to, and
to obtain indications of interest from, prospective purchasers ("Purchasers")
of the Shares, at a price per share (the "Offering Price") equal to the price
set forth on the cover page of the Prospectus (as defined below) on the date
that the Registration Statement is declared effective (the "Effective Date").

                  1.       Appointment of Placement Agent.

                           (a) The Placement Agent is hereby appointed
exclusive placement agent of the Company (subject to the Placement Agent's
right to have Selected Agents, as defined in Section 1(c) hereof, participate
in the Offering) during the Offering Period herein specified for the purposes
of assisting the Company in obtaining indications of interest from qualified
Purchasers. The Placement Agent shall not be deemed an agent of the Company for
any other purpose.

                           (b) Subject to the performance by the Company of all
of its obligations to be performed under this Agreement and to the completeness
and accuracy of all representations and warranties of the Company contained in
this Agreement, the Placement Agent hereby accepts such agency and agrees to
use its best efforts to assist the Company in obtaining indications of interest
from Purchasers pursuant to the Offering. It is understood that the Placement
Agent has no obligation to sell the Shares, but only to use its best efforts to
obtain indications of interest therefor. Furthermore, it is understood that
neither the Placement Agent nor any of its affiliates are under any obligation
to purchase any Shares in the Offering. The Placement Agent's agency hereunder
is not terminable by the Company prior to the Termination Date except as set
forth in Section 8(g).




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                           (c) The Placement Agent may engage other persons,
selected by it in its sole discretion, who are members of the National
Association of Securities Dealers, Inc., ("NASD") or who are located outside
the United States and that have executed a Selected Agents' Agreement (each
such person being hereinafter referred to as a "Selected Agent") and the
Placement Agent may allow such persons such part of the compensation and
payment of expenses payable to the Placement Agent hereunder as the Placement
Agent shall determine; provided, however, that any such compensation shall be
received pursuant to Section 4(m) hereof.

                  2. Offering Period; Escrow Agreement; Delivery and Payment.

                           (a) The "Offering Period" shall be deemed to have
commenced on November 20, 1998 (the date on which the first Preliminary
Prospectus was made available to the Placement Agent by the Company for use in
connection with the Offering). If not terminated earlier pursuant to this
Agreement, the Offering Period shall terminate at 11:59 p.m. Eastern Standard
Time on March 31, 1999, or such later time and date as may be consented to by
the Placement Agent (the "Termination Date"). If indications of interest for
the entire Offering Amount are not received prior to the end of the Offering
Period, the Offering will be terminated.

                           (b) On or prior to the Effective Date, the Company,
the Placement Agent and State Street Bank & Trust Co., as escrow agent (the
"Escrow Agent"), shall enter into an escrow agreement in customary form
mutually acceptable to the Company, the Placement Agent and the Escrow Agent
(the "Escrow Agreement"), pursuant to which an escrow account will be
established, at the Company's expense, for the benefit of the Purchasers (the
"Escrow Account"). Such Escrow Agreement shall conform in all material respects
to the requirements of Rule 15c2-4 under the Securities Exchange Act of 1934,
as amended. The Company will not request effectiveness of the Registration
Statement until indications of interest for the entire Offering Amount have
been received. When the condition set forth in the immediately preceding
sentence has been met, the Company shall request that the Commission (as
defined below) declare the Registration Statement effective. The Offering Price
shall be determined (the "Pricing") on the Effective Date. Immediately after
the Pricing, the Placement Agent will distribute confirmations and final
prospectuses to all Purchasers, and shall inform each Purchaser of the
following: (i) the closing date (the "Closing Date"), which will be scheduled
for three business days after the Pricing or such other time as may be agreed
upon by the Company and the Placement Agent, but in no event on the date prior
to the date on which the Escrow Agent has received an amount equal to the
proceeds of the sale of all of the Shares offered hereby (the "Requisite
Funds"); (ii) the Offering Price; and (iii) the total amount of funds such
Purchaser shall deposit in the Escrow Account. The Escrow Agreement shall
provide that the Escrow Agent shall notify the Company and the Placement Agent
in writing when the Purchasers have deposited funds into the Escrow Account the
Requisite Funds. At 9:00 a.m.,


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New York City time, on the Closing Date, the Escrow Agent will release the
Requisite Funds from the Escrow Account for collection by the Company and the
Placement Agent as provided in the Escrow Agreement and the Company shall
deliver the Shares to the Purchasers, which delivery may be made through the
facilities of The Depository Trust Company. The Closing shall take place at the
offices of the Placement Agent, 787 Seventh Avenue, 48th floor, New York, New
York 10019. All actions taken at the Closing shall be deemed to have occurred
simultaneously. If the Closing Date shall not have occurred on or prior to
April 5, 1999, or such later date as may be consented to by Placement Agent,
all funds together with any interest earned thereon or provided in the Escrow
Agreement shall be returned to the Purchasers who deposited such funds in the
Escrow Account and the Offering shall terminate.

                           (c) Unless delivery of the Shares is made through
the facilities of The Depository Trust Company, certificates evidencing the
Shares shall be in definitive form and shall be registered in such names and in
such denominations as the Placement Agent shall request by written notice to
the Company and shall be available at the Closing for immediate delivery
thereafter to the Purchasers. For the purpose of expediting the checking and
packaging of certificates for the Shares, the Company agrees to make such
certificates available for inspection at least 24 hours prior to the Closing
Date.

                  3. Representations and Warranties and Covenants of the
Company. The Company represents, warrants and covenants to the Placement Agent
and each Selected Dealer, if any, as follows:

                           (a) Securities Law Compliance. (i) A registration
statement (File No. 333-67599) on Form S-1 under the Act, relating to the
Offering of the Shares, including a form of prospectus subject to completion,
has been prepared by the Company in accordance with the requirements of the Act
and the rules and regulations of the Securities and Exchange Commission (the
"Commission") thereunder (the "Rules and Regulations") and has been filed with
the Commission under the Act. After the execution of this Agreement, the
Company shall file with the Commission any amendments to such registration
statement as required by the Commission or deemed necessary or appropriate by
the Company, including a form of prospectus, a copy of which amendments shall
have been furnished to and approved by the Placement Agent prior to the filing
thereof. As used in this Agreement, the term "Registration Statement" means
such registration statement, as amended at the time when it is declared
effective, including all financial statements and exhibits thereto and
including any information deemed to be part of the Registration Statement at
the Effective Date pursuant to Rule 430A under the Act; the term "Preliminary
Prospectus" means each prospectus subject to completion filed with such
registration statement or any amendment thereto (including the prospectus
subject to completion, if any, included in the Registration Statement or any
amendment thereto at the time it is declared effective); and the term
"Prospectus" means the prospectus first filed with the Commission pursuant to
Rule 424(b) under the Act, or, if no prospectus is required to be filed
pursuant to said Rule 424(b), such term means the prospectus


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included in the Registration Statement; except that if such registration
statement or prospectus is amended or such prospectus is supplemented after the
effective date of such registration statement, the terms "Registration
Statement" and "Prospectus" shall include such registration statement and
prospectus as so amended and the term "Prospectus" shall include the prospectus
as so supplemented, or both, as the case may be.

                                    (ii) Neither the Commission nor any state
securities commission has issued any order preventing or suspending the use of
any Preliminary Prospectus or has instituted or threatened to institute any
proceedings with respect to such an order. When any Preliminary Prospectus was
filed with the Commission it (i) complied in all material respects with the
requirements of, the Act and the Rules and Regulations and (ii) did not include
any untrue statement of a material fact or omit to state any material fact
required to be stated therein or necessary in order to make the statements
therein, in the light of the circumstances under which they were made, not
misleading. At the time the Registration Statement, or any amendments thereto,
becomes effective and at all times subsequent thereto up to and including the
Closing Date (i) the Registration Statement and Prospectus will comply in all
material respects to the requirements of the Act and the Rules and Regulations;
(ii) the Registration Statement will 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 (iii) the
Prospectus will not include any untrue statement of a material fact or omit to
state any material fact required to be stated therein or necessary in order to
make the statements therein, in the light of the circumstances under which they
were made, not misleading.

                           (b) Organization. The Company is a corporation duly
incorporated, validly existing and in good standing under the laws of the State
of Delaware and has all requisite corporate power and authority to own and
lease its properties, to carry on its business as currently conducted and as
proposed to be conducted (all as described in the Registration Statement and
the Prospectus (or, if the Prospectus is not in existence, the most recent
Preliminary Prospectus)), to execute and deliver this Agreement and to carry
out the transactions contemplated by this Agreement. The Company is duly
qualified or licensed to do business as a foreign corporation and is in good
standing in the State of Texas and in each jurisdiction in which the nature of
the business conducted, or the properties owned, leased or operated by it,
makes such qualification or licensing necessary, except where the failure to be
so qualified would not have a material adverse effect upon the business,
prospects and financial condition of the Company and its subsidiaries taken as
a whole (a "Material Adverse Effect").

                           (c) Capitalization. The authorized, issued and
outstanding capital stock of the Company prior to the consummation of the
transactions contemplated hereby is as set forth in the Prospectus under the
caption "Capitalization" (except for subsequent issuances, if any, pursuant to
this Agreement or as permitted under Section 3(f) of this Agreement). All
issued and outstanding shares of the Company are duly and validly issued, fully
paid and nonassessable and


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have not been issued in violation of the preemptive rights of any stockholder
of the Company. The Shares, when issued, will be validly issued, fully paid and
non-assessable and will not have been issued in violation of the preemptive
rights of any stockholder of the Company. All prior sales of the Company's
securities by the Company were either registered under the Act and applicable
state securities laws or exempt from such registration, and no security holder
has any rescission rights against the Company with respect thereto. Except as
set forth in or contemplated by the Prospectus, there are not any outstanding
warrants, options, agreements, convertible securities, rights of first refusal,
rights of first offer, preemptive rights or other rights to subscribe for or to
purchase, or other commitments pursuant to which the Company is, or may be
reasonably expected to become, obligated to issue, any shares of its capital
stock or other securities of the Company. This Offering will not cause any
anti-dilution adjustments to any outstanding securities except as reflected in
the Registration Statement. Except as set forth in the Prospectus and as
otherwise required by law, there are no restrictions on the voting or transfer
of any shares of the Company's capital stock pursuant to the Company's
Certificate of Incorporation, By-laws or other governing documents or any
agreement or other instruments to which the Company is a party or by which the
Company is bound.

                           (d) Investments; Subsidiaries' Organization. Other
than as disclosed in the Registration Statement or on Schedule 2(d) hereto, the
Company has no subsidiaries, nor does the Company own, directly or indirectly,
capital stock or other equity ownership or proprietary interests in any other
corporation, association, trust, partnership, joint venture or other entity.
Each subsidiary listed on Schedule 2(d) hereto (a "Subsidiary") is duly
incorporated, validly existing and in good standing under the laws of the state
of its incorporation and has all requisite corporate power and authority to own
and lease its properties and to carry on its business as currently conducted
and as proposed to be conducted. Each Subsidiary is qualified to do business as
a foreign corporation and is in good standing in each jurisdiction in which the
nature of the business conducted, or the properties owned, leased or operated
by it, makes such qualification necessary, except where the failure to be so
qualified would not have a Material Adverse Effect.

                           (e) Financial Statements. The financial statements,
including the notes thereto, included in the Prospectus present fairly the
financial position of the entities purported to be represented thereby as of
the dates indicated and the results of operations for the periods specified.
Except as otherwise stated in the Prospectus, such financial statements have
been prepared in conformity with generally accepted accounting principles
applied on a consistent basis in accordance with the books and records of the
Company, and are correct and complete in all material respects. The "pro forma"
and "as adjusted" financial information included in the Prospectus, fairly
present the information purported to be shown therein at the dates thereof and
for the respective periods covered thereby and all adjustments have been
properly applied. No other financial statements are required by Form S-1, or
otherwise, to be included in the Registration Statement or the Prospectus other
than those included therein.



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                           (f) Absence of Changes. Except as has been or will
be reflected in the Prospectus prior to the Closing, since the respective dates
as of which information is given in the Prospectus, (i) the Company has not
incurred any material liabilities or obligations, direct or contingent, nor has
the Company entered into any transaction that is material to the business of
the Company, (ii) there has not been (A) any change in the capital stock of, or
issuance of options, warrants or other rights to purchase capital stock of, the
Company (other than issuances of shares of Common Stock upon the exercise of
options or warrants outstanding on the date on which such information is given
in the Prospectus, or the issuance of option and other awards pursuant to the
Company's 1989 Stock Option Plan as in effect on December 31, 1997, 1998 Stock
Option Plan as initially adopted, 1993 Non-Employee Director Plan as amended
and in effect on December 31, 1997), (B) any incurrence of long-term debt in
excess of $750,000, or (C) any material adverse change in the condition
(financial or otherwise), net worth, results of operations, business, key
personnel or properties which would be material to the business, prospects or
financial condition of the Company, (iii) the Company has not become a party
to, and neither the business nor the property of the Company has become subject
of, any material litigation whether or not in the ordinary course of business
and (iv) there has been no dividend or distribution of any kind declared or
paid or made on the capital stock of the Company.

                           (g) Title. The Company has good title to all
tangible properties and assets owned by it, free and clear of all liens,
charges, encumbrances or restrictions except (i) as described in the Prospectus
or (ii) such as are not material to the Company and do not interfere with the
use of such assets in the Company's business. Except as has been or will be
reflected in the Prospectus prior to the Closing, all of the material leases
and subleases under which the Company is the lessor or sublessor of properties
or assets or under which the Company holds properties or assets as lessee or
sublessee are in full force and effect, and the Company is not in default in
any material respect under the terms or provisions of any of such leases or
subleases, and no material claim has been asserted by anyone adverse to rights
of the Company as lessor, sublessor, lessee or sublessee under any such leases
or subleases mentioned above, or affecting or questioning the right of the
Company to continued possession of the leased or subleased premises or assets
under any such lease or sublease. The Company owns or leases all such tangible
properties as are necessary to its operations as now conducted and proposed to
be conducted, and, except to the extent described in the Prospectus, the
Company presently does not anticipate the need for any material capital
expenditures to conduct its operations as now conducted as described in the
Prospectus.

                           (h) Proprietary Rights. To the best of the Company's
knowledge and except as has been or will be reflected in the Prospectus prior
to the Closing, the Company owns or possesses, adequate licenses or other
enforceable rights to use all patents, patent applications, trademarks, service
marks, trade names, corporate names, copyrights, trade secrets, processes, mask
works, licenses, inventions, formulations, technology and know-how and other
intangible property used or proposed to be used in, and that are material to,
the conduct of its business as described in or contemplated by the Prospectus
(the "Proprietary Rights"). To the best of the Company's


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knowledge and except as has been or will be reflected in the Prospectus prior
to the Closing Date, the Company and the entities from whom the Company has
acquired right has taken all necessary action to protect all of its Proprietary
Rights. Except as has been or will be set forth in the Prospectus, the Company
has not received any notice of, and there are not any facts known to the
Company that indicate the existence of (i) any infringement or misappropriation
by any third party of any of the Proprietary Rights or (ii) any claim by a
third party contesting the validity of any of the Proprietary Rights. The
Company has not received any notice of any infringement, misappropriation or
violation by the Company or any of its employees of any Proprietary Rights of
third parties, and, to the best of the Company's knowledge, neither the Company
nor any of its employees has infringed, misappropriated or otherwise violated
any Proprietary Rights of any third parties; and, to the best of the Company's
knowledge, no infringement, illicit copying, misappropriation or violation of
any intellectual property rights of any third party has occurred or will occur
with respect to any products currently being sold by the Company or with
respect to any products currently under development by the Company or with
respect to the conduct of the Company's business as currently contemplated.
Except as has been or will be described in the Prospectus, the Company is not
aware that any of its employees are obligated under any contract (including
licenses, covenants or commitments 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 the employee's best efforts to promote the
interest of the Company or that would conflict with the Company's business as
currently conducted or proposed to be conducted. To the Company's knowledge,
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 currently conducted or as proposed to be conducted, will
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 such employee is now obligated.

                           (i) Material Contracts. Each contract, agreement,
instrument, lease, license or other item required to be described in the
Registration Statement or Prospectus or filed as an exhibit to the Registration
Statement has been so described or filed, as the case may be. The description
of any such contracts is complete and accurate in all respects, does not
contain any untrue statement of a material fact or omit to state any material
fact required to be stated therein or necessary in order to make the statements
made therein, in the light of the circumstances under which they were made, not
misleading.

                           (j) Litigation. Except as described in the
Prospectus, there is no material action, suit, claim or proceeding at law or in
equity, or, to the Company's knowledge, investigation or customer complaint, by
or before any arbitrator, governmental instrumentality or other agency now
pending, or, to the knowledge of the Company, threatened against the Company
(or basis therefor known to the Company which the Company believes will result
in the foregoing), the adverse outcome of which might reasonably be expected to
have a Material Adverse Effect. The Company is not subject to any judgment,
order, writ, injunction or decree of any Federal, state,


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municipal or other governmental department, commission, board, bureau, agency
or instrumentality, domestic or foreign which might reasonably be expected to
have a Material Adverse Effect.

                           (k) Non-Defaults, Non-Contravention. The Company is
not in violation of or default under, nor will the execution and delivery of
this Agreement, the Escrow Agreement or the Placement Warrants (as described
below) (the "Offering Documents") or the consummation of the transactions
contemplated herein or therein result in a violation of or constitute a default
in the performance or observance of any obligation of the Company under (i) its
Certificate of Incorporation, its By-laws, (ii) any indenture, mortgage,
purchase order or other agreement or instrument to which the Company is a party
or by which it or its property is bound or affected or (iii) any order, writ,
injunction or decree of any court of any Federal, state, municipal or other
governmental department, commission, board, bureau, agency or instrumentality,
domestic or foreign, except where such violation or default would not have a
Material Adverse Effect. There is no existing condition, event or act which
constitutes, nor which after notice, the lapse of time or both, could
constitute, a default under any of the foregoing that would have a Material
Adverse Effect.

                           (l) Taxes. The Company has filed all Federal and
state tax returns and all material local and foreign tax returns required to be
filed by it and all such returns are true and correct in all material respects.
The Company has paid all taxes pursuant to such returns or pursuant to any
assessments received by it or which it is obligated to withhold from amounts
owing to any employee, creditor or third party. The provisions and reserves on
the books of the Company in respect of federal, state, local and other taxes
for any taxable period as to which the Company's liability for taxes has not
been finally determined or remain open to examination by applicable taxing
authorities are adequate. The Company does not have knowledge of any tax
deficiency which has been or could be assessed against the Company which,
individually or in the aggregate, would have a Material Adverse Effect.

                           (m) Compliance With Laws, Licenses, Etc. The Company
has not received notice of any violation of, or non-compliance with, any
Federal, state, local or foreign, laws, ordinances, regulations and orders
applicable to its business, the violation of, or noncompliance with which,
would have a Material Adverse Effect. The Company has all governmental licenses
and permits and other governmental certificates, authorizations and permits and
approvals (collectively, "Licenses") required by every Federal, state and local
government or regulatory body for the operation of its business as currently
conducted and the use of its properties, except where the failure to be
licensed would not have a Material Adverse Effect. The Company's Licenses are
in full force and effect and no proceeding is pending or, to the best knowledge
of the Company, threatened to revoke or limit any such License, except where
the failure to hold such License would not have a Material Adverse Effect. No
violations by the Company with respect to any License are or have been
recorded, except for such violations that are immaterial and would not cause in
the future a Material Adverse Effect.


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                           (n) Authorization of Documents and Common Stock.
Each of the Offering Documents and the Registration Statement, and the
execution, delivery and performance of the Offering Documents and the
Registration Statement, has been, or prior to the Closing will be, duly and
validly authorized by all necessary corporate action on the part of the
Company. Each of the Offering Documents, when executed and delivered,
constitute or will constitute on or prior to the Closing (assuming that such
agreements are countersigned, if necessary) the valid and legally binding
obligations of the Company, enforceable in accordance with their respective
terms, subject to (i) the availability and enforceability of equitable remedies
(regardless of whether such enforceability is considered in a proceeding or
action in equity or at law), (ii) applicable bankruptcy and other laws relating
to or affecting the rights of creditors generally and (iii) the enforcement of
the rights to indemnification and contribution hereunder and under any other
Offering Documents may be limited by federal or state securities laws or public
policy. The Company has all requisite corporate power and authority to
authorize, issue and sell the Shares to be sold to the Purchasers. The Company
has obtained or will obtain prior to the Closing Date, all consents required by
the Company or from any third party to perform any of the Company's obligations
under this Agreement or any of the other Offering Documents.

                           (o) Title to Common Stock. When certificates
representing the Shares shall have been duly delivered to the Purchasers and
payment shall have been made for the Shares, the several Purchasers shall have
good and marketable title to the Shares free and clear of all liens,
encumbrances and claims and adverse claims whatsoever (other than those created
by, or arising through the acts of, the Purchasers themselves or arising from
applicable Federal and state securities laws), and the Company shall have paid
all taxes, if any, in respect of the original issuance thereof. When
certificates representing the Placement Warrants shall have been duly delivered
to the Placement Agent, the Placement Agent or its designees shall have good
and marketable title to the Placement Warrants, and upon exercise of such
Placement Warrants, will have good and marketable title to the Common Stock
issuable upon such exercise, in each case free and clear of all liens,
encumbrances and adverse claims, whatsoever (other than those created by, or
arising through the acts of, the Purchasers, the Placement Agent or their
designees themselves or arising from applicable Federal and state securities
laws), and the Company shall have paid all taxes, if any, in respect of the
original issuance thereof.

                           (p) Brokers. No person is entitled, directly or
indirectly, to compensation from the Company for services as a broker or finder
in connection with the transactions contemplated by this Agreement other than
the Placement Agent.

                           (q) Non-Affiliated Directors. The Company's Board of
Directors has not less than two (2) directors who are independent from (as
defined in Rule 4460 of the NASD Market Place Rules), and unaffiliated with,
management of the Company.



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                           (r) Accuracy of Reports. All material reports
required to be filed by the Company within the two years prior to the date of
this Agreement under the Securities and Exchange Act of 1934, as amended (the
"Exchange Act"), have been duly filed with the SEC, complied at the time of
filing in all material respects with the requirements of their respective forms
and, except to the extent updated or superseded by the Prospectus or any
subsequently filed report, were complete and correct in all material respects
as of the dates at which the information was furnished and contained (as of the
time of such filings) no untrue statement of a material fact or omitted to
state a material fact necessary in order to make the statements contained
therein, in the light of the circumstances under which they were made, not
misleading.

                           (s) Reservation of Shares; Transfer Taxes, Etc. The
Company shall at all times reserve and keep available, out of its authorized
and unissued shares of Common Stock, solely for the purpose of effecting the
exercise of Placement Warrants, such number of shares of its Common Stock free
of preemptive rights as shall be sufficient to effect the exercise of the
Placement Warrants. The Company shall use its best efforts from time to time,
in accordance with the laws of the State of Delaware, to increase the
authorized number of shares of Common Stock if at any time the number of shares
of authorized, unissued and unreserved Common Stock shall not be sufficient to
permit the exercise of the Placement Warrants.

                           (t) Registration Rights Except as described in the
Prospectus, or as set forth in this Agreement, no person or entity has the
right, by contract or otherwise, to require registration under the Act of
shares of capital stock or other securities of the Company because of the
filing or effectiveness of the Registration Statement or otherwise in
connection with the sale of the Shares contemplated hereby, except for such
rights as have been, or prior to Closing will be, legally and effectively
waived.

                           (u) Investment Company Act. Neither the Company nor
any of its subsidiaries is, and upon consummation of the transactions
contemplated hereby none of them will be, subject to registration as an
"investment company" as defined pursuant to the Investment Company Act of 1940,
as amended.

                           (v) NASDAQ. The Common Stock of the Company is
included for trading on the Nasdaq National Market; based upon communications
with The Nasdaq Stock Market, Inc., the Offering will not violate Rule 4460(i)
of the Nasdaq Marketplace Rules.

                           (w) Accounting. The Company maintains a system of
internal accounting controls sufficient to provide reasonable assurance that
(i) transactions are executed in accordance with management's general or
specific authorization; (ii) transactions are recorded as necessary to permit
preparation of financial statements in conformity with generally accepted
accounting principles ("GAAP") and to maintain accountability for assets; (iii)
the access to the assets of the Company and each of its subsidiaries is
permitted only in accordance with


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management's general or specific authorization; and (iv) the recorded
accountability for assets is compared with existing assets at reasonable
intervals and appropriate action is taken with respect to any differences.

                           (x) No Labor Disputes. Other than as disclosed in
the Prospectus, no labor dispute with the employees of the Company is pending
or, to the knowledge of the Company, threatened that, individually or in the
aggregate, would have a Material Adverse Effect.

                           (y) Insurance. 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 business in which the Company is
engaged. The Company has no reason to believe that it will not be able to renew
existing insurance coverage from similar insurers, except as disclosed in the
Prospectus.

                           (z) Business Relationships. Except as disclosed in
the Prospectus, there are no business relationships or related party
transactions of the nature described in Item 404 of Regulation S-K of the
Commission involving the Company or any other persons referred to in such Item
404, except for such transactions as are not required under Item 404 to be
disclosed in the Prospectus.

                           (aa) Unlawful Payments. Neither the Company nor, to
the knowledge of the Company, any director, officer or employee of the Company
has, directly or indirectly, used any corporate funds for unlawful
contributions, gifts, entertainment, or other unlawful expenses relating to
political activity; made any unlawful payment to foreign or domestic government
officials or employees or to foreign or domestic political parties or campaigns
from corporate funds; violated any provision of the Foreign Corrupt Practices
Act of 1977, as amended; or made any bribe, rebate, payoff, influence payment,
kickback, or other unlawful payment.

                           (bb) Price Manipulation. Neither the Company nor, to
the Company's knowledge, any officer, director, or affiliate (as defined in the
Rules and Regulations) of the Company has taken, directly or indirectly, any
action designed to cause or result in, or which constitutes or which might
reasonably be expected to constitute, the stabilization or manipulation of the
price of the shares of Common Stock to facilitate the sale or resale of the
Shares.

                           (cc) No Business with Cuba. Neither the Company nor,
to the knowledge of the Company, any affiliate of the Company does business
with the government of Cuba or with any person or affiliate located in Cuba
within the meaning of Section 517.075 Florida Statutes.

                  4. Conditions to Placement Agent's Obligations. The
obligations of the Placement Agent hereunder are subject to the accuracy of the
representations and warranties of the


                                      -11-

<PAGE>   12





Company herein contained as of the date hereof and as of the Closing Date, to
the performance by the Company of its covenants and obligations hereunder and
to the following additional conditions:

                           (a) Effectiveness of Registration Statement. If the
Company has elected to rely on Rule 430A under the Act, the Registration
Statement shall have been declared effective, and the Prospectus (containing
the information omitted pursuant to Rule 430A) shall have been filed with the
Commission not later than the Commission's close of business on the second
business day following the date hereof or such later time and date to which the
Placement Agent shall have consented. If the Company has not elected to rely on
Rule 430A, the Registration Statement shall have been declared effective not
later than the Termination Date or such later time and date to which the
Placement Agent shall have consented. No stop order suspending the
effectiveness of the Registration Statement or any amendment thereto shall have
been issued, and no proceedings for that purpose shall have been instituted or
threatened or, to the knowledge of the Company or the Placement Agent, shall be
contemplated by the Commission.

                           (b) No Material Misstatements. The Placement Agent
shall not have advised the Company that the Registration Statement, or any
amendment thereto, contains an untrue statement of fact which, in the Placement
Agent's opinion, or in the opinion of counsel for the Placement Agent, is
material, or omits to state a fact which, in the Placement Agent's opinion, or
in the opinion of counsel for the Placement Agent, is material and is required
to be stated therein or is necessary to make the statements therein not
misleading, or that the Prospectus, or any supplement thereto, contains an
untrue statement of fact which, in the Placement Agent's opinion, or in the
opinion of counsel for the Placement Agent, is material, or omits to state a
fact which, in the Placement Agent's opinion, or in the opinion of counsel for
the Placement Agent, is material and is required to be stated therein or is
necessary to make the statements therein, in the light of the circumstances
under which they were made, not misleading.

                           (c) Compliance with Agreements. The Company shall
have complied with all agreements and satisfied all conditions on its part to
be performed or satisfied hereunder and under the other Offering Documents at
or prior to the Closing.

                           (d) Corporate Action. The Company shall have taken
all corporate action necessary to permit the valid execution, delivery and
performance of the Offering Documents by the Company, including, without
limitation, obtaining the approval of the Company's board of directors for the
execution and delivery of the Offering Documents and the performance by the
Company of its obligations hereunder and the offering contemplated hereby;

                           (e) Opinion of Counsel to the Company. The Placement
Agent shall receive the opinion of Andrews & Kurth, L.L.P., counsel to the
Company, dated as of the Closing Date, substantially to the effect that:



                                      -12-

<PAGE>   13





                           (i) the Company has been duly incorporated and is
validly existing as a corporation in good standing under the laws of the State
of Delaware;

                           (ii) the Company has the requisite corporate power
and authority necessary to own or hold its properties and conduct its business
as described in the Prospectus;

                           (iii) the Company is duly qualified to do business
as a foreign corporation and is in good standing in the State of Texas and in
each other jurisdiction in which the nature of the business conducted by it, or
the properties owned, leased or operated by it, makes such qualification
necessary, except where the failure to be so qualified would not have a
Material Adverse Effect. Other than with respect to the Subsidiaries or as
described in the Prospectus, the Company does not own, directly or indirectly,
any capital stock or other equity ownership or proprietary interests in any
other corporation, association, trust, partnership, joint venture or other
entity;

                           (iv) the authorized capitalization of the Company as
of the date of the Prospectus is as set forth under "Capitalization" in the
Prospectus; (A) all the outstanding shares of Common Stock issued by the
Company pursuant to the Company's acquisition of Oncologix, Inc. and Triplex
Pharmaceutical Corporation by the merger of such corporations with subsidiaries
of the Company and issued by the Company subsequent to the date of such mergers
and (B) the 837,989 shares of Common Stock issued to Abbott Laboratories on
November 30, 1998, have been duly authorized, are validly issued, fully paid
and nonassessable, and have not been issued in violation of the preemptive or
similar rights arising by operation of law or under the charter or bylaws of
the Company or, to such counsel's knowledge after due inquiry, under any
agreement to which the Company is a party;

                           (v) the shares of Common Stock (including the
Shares) conform in all material respects to the descriptions thereof contained
in the Prospectus under the caption "Description of Capital Stock;" the
Placement Warrants conform in all material respects to the description thereof
contained in the Prospectus;

                           (vi) the Shares and the shares of Common Stock to be
issued upon exercise of the Placement Warrants (the "Warrant Shares"), when
issued and delivered for value received by the Company, not less than the par
value thereof, in accordance with the terms of this Agreement or the Placement
Warrants, as the case may be, will be validly issued, fully paid,
non-assessable, and the issuance of such shares of Common Stock is not subject
to any preemptive or similar rights arising by operation of law or under the
charter or bylaws of the Company or, to such counsel's knowledge after due
inquiry, under any agreement to which the Company is a party; the Company has
reserved a sufficient number of shares of Common Stock for issuance upon
exercise of the Placement Warrants;



                                      -13-

<PAGE>   14





                           (vii) to such counsel's knowledge after due inquiry,
neither the filing of the Registration Statement nor the offering or sale of
the Shares or the exercise of the Placement Warrants, as contemplated by this
Agreement gives rise to any rights of any person, corporation, partnership or
other entity to require registration under the Act of any shares of Common
Stock or other securities of the Company, other than such rights which have
been waived or satisfied in accordance with the requirements of the instruments
granting such rights and the rights contained in the Placement Warrants;

                           (viii) the execution, delivery and performance of
each of the Offering Documents to which the Company is a signatory, and the
issuance of the Shares, the Placement Warrants and the Warrant Shares, have
been duly authorized by all necessary corporate action on the part of the
Company or its shareholders;

                           (ix) the Placement Agency Agreement, the Placement
Warrants and the Escrow Agreement have been duly executed and delivered by the
Company; the Placement Warrants constitute valid and legally binding
obligations of the Company, enforceable against the Company in accordance with
their terms under the law of the State of New York, expressed to govern the
same, subject to bankruptcy, insolvency, fraudulent transfer, reorganization,
moratorium and other similar laws of general applicability relating to or
affecting creditors' rights and to general principles of equity (including,
without limitation, principles of reasonableness, materiality, good faith and
fair dealing, regardless of whether considered in a proceeding in equity or at
law);

                           (x) the certificates evidencing the Shares comply in
all material respects as to form under the Delaware General Corporation Law;

                           (xi) except as described in the Prospectus, to such
counsel's knowledge after due inquiry, (i) there are no pending or threatened
legal or governmental proceedings to which the Company is a party, which might
reasonably be expected to materially adversely affect the business, property,
financial condition, or operations of the Company or seek to enjoin or prevent
the issuance, sale and delivery of the Shares or question the validity of the
Offering Documents or actions to be taken thereunder, and (ii) there are no
governmental proceedings or regulations that are required to be described or
referred to in the Registration Statement which are not so described or
referred to;

                           (xii) the execution and delivery of this Agreement
and the other Offering Documents and the consummation of the transactions
contemplated hereby and thereby, will not result in a breach or violation of,
or constitute a default under, (i) the Certificate of Incorporation or By-laws
of the Company, (ii) any contract, indenture, mortgage, loan agreement, lease,
joint venture, or other agreement or instrument filed as an exhibit to the
Registration Statement (other than with respect to covenants or agreements of a
financial or numerical nature or requiring computation, as to which such
counsel need express no opinion) or (iii) any order, rule, regulation,


                                      -14-

<PAGE>   15





writ, injunction, or decree known to such counsel of any government,
governmental instrumentality, or court, domestic or foreign, having
jurisdiction over the Company or any of its subsidiaries or any of their
properties or business, other than, in the case of clauses (ii) and (iii), any
such default which would not have a Material Adverse Effect;

                           (xiii) the Registration Statement has become
effective under the Act, and to such counsel's knowledge, no stop order
suspending the effectiveness of the Registration Statement has been issued, and
no proceedings for that purpose have been instituted or are pending before, or
threatened by, the Commission;

                           (xiv) the Registration Statement, when it became
effective, and the Prospectus (except for the financial statements, related
notes and schedules thereto, and other financial and statistical data contained
therein, as to which such counsel need express no opinion) on the date of
filing or date thereof complied as to form in all material respects with the
applicable requirements of the Act and the Rules and Regulations;

                           (xv) such counsel does not know of any contracts or
agreements to which the Company is a party of a character required to be
summarized or described in the Prospectus or to be filed as exhibits to the
Registration Statement which are not so summarized, described, or filed;

                           (xvi) to the such counsel's knowledge, no
authorization, approval, consent, or license of any governmental or regulatory
authority or agency is necessary in connection with the authorization,
issuance, transfer, sale, or delivery of the Shares by the Company, the
execution, delivery, and performance of this Agreement by the Company or the
taking of any action contemplated herein, or the issuance of the Placement
Warrants or the Warrant Shares, other than registrations or qualifications of
the Shares under applicable state or foreign securities or Blue Sky laws and
registration under the Act or as may be required by the National Association of
Securities Dealers, Inc. (the "NASD");

                           (xvii) upon the issuance of the Shares, the
Placement Warrants and the Warrant Shares, each of the Purchasers or the
Placement Agent and its designees, as the case may be, shall acquire such
securities, free and clear of all pledges, liens, claims or encumbrances
imposed by the Company under its Certificate of Incorporation or Bylaws or, to
such counsel's knowledge, under any agreement to which the Company is a party;
and

                           (xvii) the Company is not, and upon the consummation
of the transactions contemplated by this Agreement will not be an "investment
company" as defined pursuant to the Investment Company Act of 1940, as amended.




                                      -15-

<PAGE>   16





                           Such opinion shall include a statement to
substantially the following effect:

                  "In the course of the preparation of the Registration
         Statement and Prospectus we have among other things: (i) made
         inquiries concerning various legal matters and have reviewed certain
         corporate records, documents and proceedings; (ii) we have
         participated in conferences with officers and other representatives of
         the Company, representatives of Arthur Andersen LLP, independent
         public accountants for the Company, and the Placement Agent and their
         counsel during which the contents of the Registration Statement and
         the Prospectus and related matters were discussed. We have not,
         however, independently verified the accuracy, completeness or fairness
         of the statements contained in the Registration Statement and the
         Prospectus. On the basis of the foregoing and relying as to
         materiality to a large extent upon facts provided to us by officers
         and other representatives of the Company, we advise you that nothing
         has come to our attention that would lead us to believe that the
         Registration Statement and the Prospectus included therein at the time
         the Registration Statement became effective (except for financial
         statements and notes thereto and other financial and statistical data
         included or incorporated by reference therein, as to which we express
         no opinion) contained any untrue statement of a material fact or
         omitted to state a material fact required to be stated therein or
         necessary in order to make the statements therein, in the light of the
         circumstances under which they were made, not misleading, or that the
         Prospectus (except for financial statements and notes thereto and
         other financial and statistical data included or incorporated by
         reference therein, as to which we express no opinion) contains any
         untrue statement of a material fact 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."

Such opinion shall also cover such matters incident to the transactions
contemplated hereby as the Placement Agent or counsel for the Placement Agent
shall reasonably request.

                  In rendering such opinion, such counsel may rely upon
certificates of any officer of the Company or public officials as to matters of
fact.

                           (f) Opinion of Patent Counsel. The Placement Agent
shall receive (unless waived in writing by the Placement Agent) the opinion of
patent counsel to the Company (which such counsel shall be satisfactory to the
Placement Agent), dated the Closing Date in the form and substance satisfactory
to counsel for the Placement Agent.

                           (g) Comfort Letter. The Company shall cause Arthur
Andersen, LLP, the Company's independent public accountants, to address and
deliver to the Company and the Placement Agent a letter or letters (which
letters are frequently referred to as "Comfort Letters") dated as of the
Effective Date and the Closing Date.

                                      -16-

<PAGE>   17





                           (h) Officer's Certificate. The Placement Agent shall
receive an Officer's Certificate substantially in the form of Exhibit A hereto
and a Secretary's Certificate substantially in the form of Exhibit B hereto,
signed by the appropriate parties and dated as of the Closing Date.

                           (i) Escrow Agreement. The Placement Agent shall
receive a copy of a duly executed Escrow Agreement with State Street Bank &
Trust Company.

                           (j) Transmittal Letters. The Placement Agent shall
receive copies of all letters from the Company to the investors transmitting
the Common Stock and shall receive a letter from the Company confirming
transmittal of the securities to the investors.

                           (k) NASDAQ. The Shares and the Common Stock issuable
upon exercise of the Placement Warrants, shall have been duly authorized for
quotation on the Nasdaq National Market, subject to notice of issuance.

                           (l) Blue Sky. A summary blue sky survey, at the sole
cost of the Company (including, without limitation, the legal fees and
disbursements in connection therewith), shall be prepared by counsel to the
Company stating the extent to which and the conditions upon which offers and
sales of the Shares may be made in certain jurisdictions.

                           (m) Placement Fees and Expenses. (i) At the Closing,
pursuant to the terms of the Escrow Agreement, the Escrow Agent shall release
the funds held in the Escrow Account for collection by the Company and the
Placement Agent. The Company agrees that the Placement Agent shall receive a
commission (the "Cash Commission") equal to (A) eight percent (8%) of the
aggregate purchase price of all of the Shares sold in the Offering to
non-affiliates of the Company and (B) five percent (5%) of the aggregate
purchase price of all of the Shares sold in the Offering to affiliates of the
Company. The Company further agrees to reimburse the Placement Agent for all
out-of-pocket expenses incurred by the Placement Agent in connection with such
Offering as more fully set forth in section 5(l) below, in an amount not to
exceed $150,000 in the aggregate. In addition, at the Closing, the Company will
sell to the Placement Agent and/or its designees, for $.001 per warrant,
warrants in the form attached hereto as Exhibit C (the "Placement Warrants") to
acquire a number of newly issued shares of Common Stock equal, but not greater
than, ten percent (10%) of the number of shares of Common Stock issued and sold
in the Offering, exercisable for a period of five (5) years from the Effective
Date and commencing 12 months after the Effective Date at an exercise price
equal to one hundred fifty percent (150%) of the Offering Price. The Company
agrees with the Placement Agent and its successors and assigns that the
securities underlying the Placement Warrants will not be subject to redemption
by the Company nor will they be callable or mandatorily convertible by the
Company. The Placement Warrants cannot be transferred, sold, assigned or
hypothecated for 12 months except that they may be assigned in whole or in part
during such period to any NASD member participating in the Offering or any
officer


                                      -17-

<PAGE>   18





of the Placement Agent or any such NASD member. The Placement Warrants will
contain a cashless exercise feature and certain registration rights.

                                    (ii) The Cash Commission and Placement
Warrants as set forth in this Agreement shall be paid to the Placement Agent
with respect to any investment by any investors introduced to the Company by
the Placement Agent ("Covered Investors") in the event that any such Covered
Investor purchases any securities from the Company during the 12 months
following the Closing in a transaction other than a public offering registered
under the Act.

                           (n) No Adverse Changes. There shall not have
occurred, at any time prior to the Closing (i) any domestic or international
event, act or occurrence which has materially disrupted, or in the Placement
Agent's determination will in the immediate future materially disrupt, the
securities markets of the United States; (ii) a general suspension of, or a
general limitation on prices for, trading in securities on the New York Stock
Exchange, the American Stock Exchange or the NASDAQ National Market; (iii) any
outbreak of major hostilities or other national or international calamity; (iv)
any banking moratorium declared by a federal, Texas or New York state
authority; (v) any moratorium declared in foreign exchange trading by major
international banks or other persons; (vi) any material interruption in the
mail service or other means of communication within the United States; (vii)
since the respective dates as of which information is given in the Registration
Statement or the Prospectus, any material adverse change in the business,
properties, assets, results of operations, financial condition or prospects of
the Company; or (viii) any change in the market for securities in general or in
political, financial, or economic conditions which, in the Placement Agent's
reasonable judgment, makes it inadvisable to proceed with the offering, sale,
and delivery of the Shares.

                           (o) Waiver of Registration Rights. All rights,
whether by contract or otherwise, that any person has, to require registration
under the Act of shares of capital stock or other securities of the Company
because of the filing or effectiveness of the Registration Statement or
otherwise in connection with the sale of the Shares contemplated hereby, shall
have been legally and effectively waived.

                           (p) Lock-Ups. The Placement Agent shall have
received from the officers and directors of the Company, and the Company shall
have used its reasonable best efforts to obtain from each stockholder with
beneficial ownership in excess of 5% of the outstanding shares of the Company's
Common Stock, an agreement that they will not, directly or indirectly, offer,
sell, contract to sell, make any short sale (including, but not limited to, a
"short against the box"), pledge, or otherwise dispose of any shares of Common
Stock or any securities convertible into or exercisable for, or any rights to
purchase or acquire, Common Stock for a period of 180 days after the date that
the Registration Statement is filed with the Commission, without the prior
written consent of the Placement Agent.



                                      -18-

<PAGE>   19





                           (q) No Amendments. No amendment to the Registration
Statement or the Prospectus (other than the filing of the Prospectus pursuant
to Rule 424(b) of the Act or a Registration Statement, if any, pursuant to Rule
462(b) of the Act) shall have been filed from the date on which the
Registration Statement is declared effective without the prior consent of the
Placement Agent.

                  5. Covenants of the Company. The Company covenants and agrees
as follows:

                           (a) Registration Statement Filing. The Company will
use its best efforts to cause the Registration Statement and any amendments
thereto to become effective pursuant to the terms hereof. If required, the
Company will file the Prospectus and any amendment or supplement thereto with
the Commission in the manner and within the time period required by Rule 424(b)
under the Act. During any time when a prospectus relating to the Shares is
required to be delivered under the Act, the Company (i) will comply with all
requirements imposed upon it by the Act and the Rules and Regulations to the
extent necessary to permit the continuance of sales of or dealings in the
Shares in accordance with the provisions hereof and of the Prospectus, as then
amended or supplemented, and (ii) will not file with the Commission any
prospectus, any amendment or supplement to any prospectus or any amendment to
the Registration Statement of which the Placement Agent shall not previously
have been advised and furnished with a copy a reasonable period of time prior
to the proposed filing and as to which the Placement Agent shall not have given
its consent.

                           (b) Notices of Certain Events. As soon as the
Company is advised or obtains knowledge thereof, the Company will advise the
Placement Agent: (i) when the Registration Statement, as amended, has become
effective; (ii) if the provisions of Rule 430A promulgated under the Act will
be relied upon, when the Prospectus has been filed in accordance with said Rule
430A and when any post-effective amendment to the Registration Statement
becomes effective; (iii) of any request made by the Commission for amending the
Registration Statement, for supplementing any Preliminary Prospectus or the
Prospectus or for additional information; or (iv) of the issuance by the
Commission of any stop order suspending the effectiveness of the Registration
Statement or any post-effective amendment thereto or any order preventing or
suspending the use of any Preliminary Prospectus or the Prospectus or any
amendment or supplement thereto or the institution or threat of any
investigation or proceeding for that purpose, and will use its best efforts to
prevent the issuance of any such order and, if issued, to obtain the lifting
thereof as soon as possible.

                           (c) Prospectus. The Company consents to the use of
the Prospectus (and any amendment or supplement thereto) by the Placement Agent
in connection with the solicitation of indications of interest in purchasing
the Shares and for such period of time thereafter as the Prospectus is required
by law to be delivered in connection therewith. If, at any time when a
prospectus relating to the Shares is required to be delivered under the Act,
any event occurs as a result of which the Prospectus, as then amended or
supplemented, would include any untrue


                                      -19-

<PAGE>   20





statement of a material fact or omit to state a material fact necessary to make
the statements therein not misleading, or if it becomes necessary at any time
to amend or supplement the Prospectus to comply with the Act or the Rules and
Regulations, the Company promptly will so notify the Placement Agent and,
subject to Section 5(a) hereof, will prepare and file with the Commission an
amendment to the Registration Statement or an amendment or supplement to the
Prospectus which will correct such statement or omission or effect such
compliance, each such amendment or supplement to be reasonably satisfactory to
counsel to the Placement Agent.

                           (d) Rule 158. As soon as practicable, but in any
event not later than 45 days after the end of the 12-month period beginning on
the day after the end of the fiscal quarter of the Company during which the
effective date of the Registration Statement occurs (90 days in the event that
the end of such fiscal quarter is the end of the Company's fiscal year), the
Company will make generally available to its security holders, in the manner
specified in Rule 158(b) of the Rules and Regulations, and to the Placement
Agent, an earnings statement which will be in the detail required by, and will
otherwise comply with, the provisions of Section 11(a) of the Act and Rule
158(a) of the Rules and Regulations, which statement need not be audited unless
required by the Act or the Rules and Regulations, covering a period of at least
12 consecutive months after the effective date of the Registration Statement.

                           (e) Public Documents. For a period of three years
following the Closing of the Offering, the Company will furnish to the
Placement Agent: (i) as soon as practicable (but in the case of the annual
report of the Company to its stockholders, within 120 days after the end of
each fiscal year of the Company) one copy of: (A) its annual report to its
stockholders (which annual report shall contain financial statements audited in
accordance with generally accepted accounting principles in the United States
of America by a firm of certified public accountants of recognized standing),
(B) if not included in substance in its annual report to stockholders, its
annual report on Form 10-K, (C) each of its quarterly reports to its
stockholders, if any, and if not included in substance in its quarterly reports
to stockholders, its quarterly report on Form 10-Q, (D) each of its current
reports on Form 8-K; (E) as soon as they are available, copies of all other
information (financial or otherwise) mailed to the Company's stockholders; and
(ii) upon reasonable request, any other information prepared by the Company
that is generally available to the public.

                           (f) Transfer Agent. The Company will maintain a
Transfer Agent and, if necessary under the jurisdiction of incorporation of the
Company, a Registrar (which may be the same entity as the Transfer Agent) for
its Common Stock.

                           (g) Copies of Registration Statement, Prospectuses.
The Company will furnish, without charge, to the Placement Agent or on the
Placement Agent's order, at such place as the Placement Agent may designate,
copies of each Preliminary Prospectus, the Registration Statement and any
pre-effective or post-effective amendments thereto (two of which copies will be
signed and will include all financial statements and exhibits) and the
Prospectus, and all amendments


                                      -20-

<PAGE>   21





and supplements thereto, in each case as soon as available and in such
quantities as the Placement Agent may reasonably request.

                           (h) Nasdaq Listing Application. The Company will
file a listing application for the Shares and the Common Stock issuable upon
exercise of the Placement Warrants with the Nasdaq National Market prior to the
Closing Date.

                           (i) No Manipulation. Neither the Company nor any of
its officers or directors, nor affiliates of any of them (within the meaning of
the Rules and Regulations) will take, directly or indirectly, any action
designed to, or which might in the future reasonably be expected to cause or
result in the manipulation of the price of any securities of the Company in
violation of the Exchange Act.

                           (j) Filings with the Commission. The Company will
timely file all such reports, forms or other documents as may be required from
time to time, under the Act, the Rules and Regulations, the Exchange Act, and
the rules and regulations thereunder, and all such reports, forms and documents
filed will comply as to form and substance with the applicable requirements
under the Act, the Rules and Regulations, the Exchange Act and the rules and
regulations thereunder.

                           (k) Use of Proceeds. The net proceeds of the
Offering will be used by the Company substantially as set forth in the
Prospectus. The Company shall not use any of the proceeds from this Offering to
repurchase, redeem or otherwise acquire shares of capital stock of the Company
held by, or to repay indebtedness of the Company to, any of the current
executive officers, directors or principal stockholders of the Company.

                           (l) Expenses of Offering. The Company shall be
responsible for and shall bear all expenses incurred by the Company in
connection with the proposed Offering, including but not limited to, the costs
of preparing and duplicating the Registration Statement and all exhibits
thereto; the costs of preparing, printing and filing with the Securities and
Exchange Commission (the "SEC") the Registration Statement and amendments,
post-effective amendments and supplements thereto; preparing, duplicating and
delivering exhibits thereto and copies of the preliminary, final and
supplemental prospectus; preparing, duplicating and delivering (including by
facsimile) all selling documents, including but not limited to the Registration
Statement and Prospectus, this Agreement, blue sky memorandum and stock
certificates; blue sky fees, filing fees and legal fees and disbursements of
counsel in connection with blue sky filings; and fees and disbursements of the
transfer agent (collectively, the "Company Expenses"). The Company has
previously paid to the Placement Agent an expense allowance equal to fifteen
thousand dollars ($15,000) to cover the initial costs of the Placement Agent's
mailing, telephone, telecopy and travel to due diligence meetings. The Company
shall be responsible for and bear all actual, accountable out-of-pocket
expenses incurred by the Placement Agent, including but not limited to legal
fees and disbursements, filing fees with the NASD, telephone, travel, mailing
and other similar expenses, up to and not


                                      -21-

<PAGE>   22





exceeding $150,000 in aggregate (the "Placement Agent Expenses"). If the
proposed financing is not completed because the Company prevents it or because
of a breach by the Company of any covenants, representations or warranties
contained herein, or because indications of interest for the Offering Amount
have not been received by the Termination Date, then the Company shall
reimburse the Placement Agent for such Placement Agent Expenses (in addition to
the Company Expenses for which the Company shall in all events remain liable).

                           (m) Notification. The Company shall notify the
Placement Agent immediately, and in writing, (A) when any event shall have
occurred during the period commencing on the date hereof and ending on the
Closing Date as a result of which the Offering Documents would include 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
in the light of the circumstances under which they were made and (B) of the
receipt of any notification with respect to the modification, rescission,
withdrawal or suspension of the qualification or registration of the Common
Stock, or of any exemption from such registration or qualification, in any
jurisdiction. The Company will use its commercially reasonable best efforts to
prevent the issuance of any such modification, rescission, withdrawal or
suspension and, if any such modification, rescission, withdrawal or suspension
is issued and the Placement Agent so requests, to obtain the lifting thereof as
promptly as possible.

                           (n) Blue Sky. The Company will use its commercially
reasonable best efforts to qualify the Common Stock for offering and sale under
exemptions from qualification or registration requirements under the securities
or "blue sky" laws of such jurisdictions as the Placement Agent may reasonably
request; provided however, that the Company will not be obligated to qualify as
a dealer in securities in any jurisdiction in which it is not so qualified. The
Company will not consummate any sale of Common Stock in any jurisdiction in
which it is not so qualified or in any manner in which such sale may not be
lawfully made.

                           (o) No Offerings. Pending completion or termination
of the Offering in accordance with the terms of this Agreement, the Company
agrees that it will not enter into an agreement (whether binding or not) with
any other person or entity relating to a possible public or private offering or
placement of its securities (other than in connection with a corporate
partnership, strategic alliance or government funding).

                           (p) No Statements. Unless required by law, the
Company shall not use the name of the Placement Agent or any officer, director,
employee or shareholder thereof in any written press release without the
consent of the Placement Agent, which consent shall not be unreasonably
withheld.

                  6.       Indemnification.



                                      -22-

<PAGE>   23





                           (a) The Company agrees to indemnify and hold
harmless the Placement Agent and each Selected Agent, if any, and their
respective partners, affiliates, shareholders, directors, officers, agents,
advisors, representatives, employees, counsel and controlling persons within
the meaning of the Act (a "Paramount Indemnified Party") against any and all
losses, liabilities, claims, damages and expenses whatsoever (and all actions
in respect thereof), and to reimburse each such Paramount Indemnified Party for
legal fees and related expenses as incurred (including, but not limited to the
costs of giving testimony or furnishing documents in response to a subpoena or
otherwise, the costs of investigating, preparing, pursuing or defending any
such action or claim whether or not pending or threatened and whether or not
the Placement Agent or any Paramount Indemnified Party is a party thereto), in
so far as such losses, liabilities, claims, damages or expenses arise out of,
relate to, are incurred in connection with or are in any way a result of (i)
the engagement of the Placement Agent pursuant to this Agreement and in
connection with the transactions contemplated by this Agreement and the other
Offering Documents (the "Engagement"), including any modifications or future
additions to such Engagement and related activities prior to the date hereof,
(ii) any act by the Placement Agent or any Paramount Indemnified Party taken in
connection with the Engagement, (iii) a breach of any representation, warranty,
covenant, or agreement of the Company contained in this Agreement, (iv) the
employment by the Company of any device, scheme or artifice to defraud, or the
engaging by the Company in any act, practice or course of business which
operates or would operate as a fraud or deceit, or any conspiracy with respect
thereto, in connection with the sale of the Common Stock, or (v) any untrue
statement or alleged untrue statement of a material fact contained in the
Registration Statement or Prospectus or the omission or alleged omission
therefrom of a material fact necessary in order to make the statements therein,
in the light of the circumstances under which they were made, not misleading;
provided, however, that the Company will not be liable in any such case if and
to the extent that any such loss, claim, damage, liability or expense (A) has
been judicially determined to have resulted from the willful misconduct, gross
negligence or unlawful act by the Placement Agent or such Paramount Indemnified
Party or (B) arises out of or is based upon an untrue statement or alleged
untrue statement or omission or alleged omission so made in conformity with
information furnished by the Placement Agent or any such Paramount Indemnified
Party in writing specifically for use in therein;

                           (b) The Company agrees to indemnify and hold
harmless a Paramount Indemnified Party to the same extent as the foregoing
indemnity, and subject to the limitations set forth therein, against any and
all loss, liability, claim, damage and expense whatsoever directly arising out
of the exercise by any person of any right under the Act or Exchange Act or the
securities or Blue Sky laws of any state on account of violations by the
Company of the representations, warranties or agreements set forth in Section 3
hereof.

                           (c) The Placement Agent agrees to indemnify and hold
harmless the Company, the Company's directors, officers, employees, counsel,
advisors, representatives and agents and controlling persons within the meaning
of the Act (a "Company Indemnified Party") and


                                      -23-

<PAGE>   24





each and all of them, to the same extent as set forth in Section 6(a)(v) of the
foregoing indemnity from the Company to the Placement Agent, but only with
reference to information, relating to the Placement Agent, furnished in writing
to the Company by the Placement Agent specifically for inclusion in the
Registration Statement and only to the extent that any losses, claims, damages,
and liabilities in respect of which indemnification claimed are finally
judicially determined to have resulted primarily and directly from the bad
faith or gross negligence of the Placement Agent.

                           (c) Promptly after receipt by a person entitled to
indemnification pursuant to subsection (a), (b) or (c) (an "indemnified party")
of this Section 6 of notice of the commencement of any action, the indemnified
party will, if a claim in respect thereof is to be made against a person
granting indemnification (an "indemnifying party") under this Section 6, notify
in writing the indemnifying party of the commencement thereof; but the omission
so to notify the indemnifying party will not relieve it from any liability
which it may have to the indemnified party otherwise than under this Section 6.
In case any such action is brought against an indemnified party, and it
notifies the indemnifying party of the commencement thereof, the indemnifying
party will be entitled to participate in, and, to the extent that it may wish,
jointly with any other indemnifying party similarly notified, to assume the
defense thereof, subject to the provisions herein stated, with counsel
reasonably satisfactory to the indemnified party, and after notice from the
indemnifying party to the indemnified party of its election so to assume the
defense thereof, the indemnifying party will not be liable to the indemnified
party for any legal or other expenses subsequently incurred by the indemnified
party in connection with the defense thereof other than reasonable costs of
investigation incurred at the request of the indemnifying party. The
indemnified party shall have the right to employ separate counsel in any such
action and to participate in the defense thereof, but the fees and expenses of
such counsel shall not be at the expense of the indemnifying party if the
indemnifying party has assumed the defense of the action with counsel
reasonably satisfactory to the indemnified party; provided that the fees and
expenses of such counsel shall be at the expense of the indemnifying party if
(i) the employment of such counsel has been specifically authorized in writing
by the indemnifying party or (ii) the named parties to any such action
(including any impleaded parties) include both the indemnified party or parties
and the indemnifying party and, in the opinion of counsel of the indemnified
party, a conflict of interest exists between such parties in which case the
indemnifying party shall not have the right to assume the defense of such
action on behalf of the indemnified party or parties, it being understood,
however, that the indemnifying party shall not, in connection with any one such
action or separate but substantially similar or related actions in the same
jurisdiction arising out of the same general allegations or circumstances, be
liable for the reasonable fees and expenses of more than one separate firm of
attorneys for the indemnified party or parties. No settlement, compromise,
consent to entry of judgment or other termination of any action (collectively,
"Terminations") in respect of which a Paramount Indemnified Party may seek
indemnification hereunder (whether or not any Paramount Indemnified Party is a
party thereto) shall be made without the prior written consent of the Paramount
Indemnified Party, which such consent may be withheld at the sole discretion of
such Paramount Indemnified Party, provided, however, that the foregoing
requirement of prior written consent for Terminations shall not apply to the
Placement


                                      -24-

<PAGE>   25





Agent who may agree to such Terminations without the prior written consent of
any Paramount Indemnified Party.

                           (e) Notwithstanding any of the provisions of this
Agreement, the aggregate indemnification or contribution of the Placement Agent
for or on account of any losses, claims, damages, liabilities or actions under
this Section 6, Section 7 or any other applicable section of this Agreement,
shall not exceed the Cash Commissions actually paid to the Placement Agent. The
respective indemnity and contribution agreements by the Company and the
Placement Agent contained in subsections (a), (b), (c) and (d) of this Section
6 and Section 7, and the covenants, representations and warranties of the
Company and the Placement Agent set forth in Sections 1, 2, 3, 4 and 5 shall
remain operative and in full force and effect regardless of (i) any
investigation made by the Placement Agent, on the Placement Agent's behalf or
by or on behalf of any person who controls the Placement Agent, the Company or
any controlling person of the Company or any director or officer of the
Company, (ii) acceptance of any of the Common Stock and payment therefor or
(iii) any termination of this Agreement, and shall survive the delivery of the
Common Stock, and any successor of the Placement Agent or of the Company or of
any person who controls the Placement Agent or the Company, as the case may be,
shall be entitled to the benefit of such respective indemnity and contribution
agreements. The respective indemnity and contribution agreements by the Company
and the Placement Agent contained in subsections (a), (b) and (c) of this
Section 6 and Section 7 shall be in addition to any liability which the Company
and the Placement Agent may otherwise have.

                  7.       Contribution.

                           (a) To provide for just and equitable contribution,
if (i) an indemnified party makes a claim for indemnification pursuant to
Section 6 but it is found in a final judicial determination, by a court of
competent jurisdiction, not subject to further appeal, that such
indemnification may not be enforced in such case, even though this Agreement
expressly provides for indemnification in such case, or (ii) any indemnified or
indemnifying party seeks contribution under the Act, the Exchange Act, or
otherwise, then the Company (including for this purpose any contribution made
by or on behalf of any officer, director, employee or agent for the Company, or
any controlling person of the Company), on the one hand, and the Placement
Agent and any Selected Agents (including for this purpose any contribution by
or on behalf of an indemnified party), on the other hand, shall contribute to
the losses, liabilities, claims, damages, and expenses whatsoever to which any
of them may be subject, in such proportions as are appropriate to reflect the
relative benefits received by the Company, on the one hand, and the Placement
Agent and the Selected Agents, on the other hand; provided, however, that if
applicable law does not permit such allocation, then other relevant equitable
considerations such as the relative fault of the Company and the Placement
Agent and the Selected Agents in connection with the facts which resulted in
such losses, liabilities, claims, damages, and expenses shall also be
considered. In no case shall the Placement Agent or a Selected Agent be
responsible for a portion of the contribution obligation in excess of the


                                      -25-

<PAGE>   26





compensation received by it pursuant to Section 4 or 5 hereof or the Selected
Agent Agreement, as the case may be. No person guilty of a fraudulent
misrepresentation shall be entitled to contribution from any person who is not
guilty of such fraudulent misrepresentation. For purposes of this Section 7,
each person, if any, who controls the Placement Agent or a Selected Dealer
within the meaning of Section 15 of the Act or Section 20(a) of the Exchange
Act and each officer, director, stockholder, employee and agent of the
Placement Agent or a Selected Agent, shall have the same rights to contribution
as the Placement Agent or the Selected Agent, and each person, if any, who
controls the Company within the meaning of Section 15 of the Act or Section
20(a) of the Exchange Act and each officer, director, employee and agent of the
Company, shall have the same rights to contribution as the Company, subject in
each case to the provisions of this Section 7. Anything in this Section 7 to
the contrary notwithstanding, no party shall be liable for contribution with
respect to the settlement of any claim or action effected without its written
consent. This Section 7 is intended to supersede any right to contribution
under the Act, the Exchange Act, or otherwise.

                  8.       Miscellaneous.

                           (a) Survival. Any termination of the Offering
without any Closing shall be without obligation on the part of any party except
that the provisions regarding fees and expenses contained in Sections 4(m) and
5(l), the indemnification provided in Section 6 hereof and the contribution
provided in Section 7 hereof shall survive any termination and shall survive
any Closing.

                           (b) Representations, Warranties and Covenants to
Survive Delivery. Except as provided in Section 8(a), the respective
representations, warranties, indemnities, agreements, covenants and other
statements of the Company and the Placement Agent as of the date hereof shall
survive execution of this Agreement and delivery of the Shares and the
termination of this Agreement.

                           (c) No Other Beneficiaries. This Agreement is
intended for the sole and exclusive benefit of the parties hereto and their
respective successors and controlling persons, and no other person, firm or
corporation shall have any third-party beneficiary or other rights hereunder.

                           (d) Governing Law. This Agreement shall be governed
by and construed in accordance with the law of the State of New York without
regard to conflict of law provisions.

                           (e) Counterparts. This Agreement may be signed in
counterparts with the same effect as if both parties had signed one and the
same instrument.

                           (f) Notices. Any communications specifically
required hereunder to be in writing, if sent to the Placement Agent, will be
mailed, delivered and confirmed to it at Paramount Capital, Inc., 787 Seventh
Avenue, 48th Floor, New York, New York, 10019, Att: Michael S. Weiss


                                      -26-

<PAGE>   27





and if sent to the Company, will be mailed, delivered or telegraphed and
confirmed to it at Aronex Pharmaceuticals, Inc., 8707 Technology Forest Place,
The Woodlands, Texas 77381-1191, Attn: Chief Executive Officer.

                           (g) Termination. Subject to the general survival
provisions contained in Sections 8(a) and 8(b) and, in the event of a
termination by the Company, provided that the Company pays all accountable
expenses of the Placement Agent as provided in Section 5(l), this Agreement may
be terminated by either party prior to the end of the Offering Period upon
written notice to the other party.

                           (h) Entire Agreement. This Agreement constitutes the
entire agreement of the parties with respect to the matters herein referred and
supersedes all prior agreements and understandings, written and oral, between
the parties with respect to the subject matter hereof. Neither this Agreement
nor any term hereof may be changed, waived or terminated orally, but only by an
instrument in writing signed by the party against which enforcement of the
change, waiver or termination is sought.

                           (i) Nothing contained herein or otherwise shall
create a partnership or joint venture between the Placement Agent and the
Company.

                           (j) The headings and captions of the various
subdivisions of this Agreement are for convenience or reference only and shall
in no way modify or affect the meaning or construction of any of the terms or
provisions hereof.





                                      -27-

<PAGE>   28





                  If you find the foregoing is in accordance with our
understanding, kindly sign and return to us a counterpart hereof, whereupon
this instrument along with all counterparts will become a binding agreement
between us.

                                        Very truly yours,

                                        ARONEX PHARMACEUTICALS, INC.


                                        By:
                                           -----------------------------------
                                        Name: Geoffrey Cox
                                        Title:   Chief Executive Officer


Agreed to by:

PARAMOUNT CAPITAL, INC.


By:
   --------------------------------
Name:    Lindsay A. Rosenwald, M.D.
Title:   Chairman



                                      -28-

<PAGE>   29





                                                                  SCHEDULE 2(d)

                                  SUBSIDIARIES


Triplex Pharmaceuticals, Inc.
Oncologix, Inc.
Aronex Europe Limited







                                      -29-

<PAGE>   30





                                                                      EXHIBIT A


                          ARONEX PHARMACEUTICALS, INC.

                             OFFICER'S CERTIFICATE

                  I, Geoffrey F. Cox, certify that I am the Chairman of the
Board of Directors and Chief Executive Officer of Aronex Pharmaceuticals, Inc.,
a Delaware corporation (the "Company"), and that, as such, I am authorized to
execute this certificate on behalf of the Company. All capitalized terms used
herein but not otherwise defined herein shall the meanings ascribed to such
terms in the Placement Agency Agreement dated as of November 19, 1998 between
the Company and Paramount Capital, Inc. (the "Placement Agency Agreement").
Reference is made herein to the closing held on February __, 1999 (the "Closing
Date").

                  I do hereby certify that I have carefully examined all of the
Offering Documents and do hereby further certify that:

                  1. All of the representations and warranties of the Company
contained in the Placement Agency Agreement are true and correct in all
material respects on the Closing Date with the same force and effect as if made
on and as of the Closing Date, and the Company has performed in all material
respects all covenants and agreements and has satisfied all conditions in the
Placement Agency Agreement to be performed or satisfied on its part before the
Closing Date.

                  2. Since the date of the most recent financial statements and
the information included in the Registration Statement, there has been no
material adverse change in the condition (financial or other), earnings,
business, properties or prospects of the Company taken as a whole, whether or
not arising from transactions in the ordinary course of business, nor has there
occurred any material event required to be set forth in the Registration
Statement, including, without limitation, in accordance with Section 3(g) of
the Placement Agency Agreement.

                  This Certificate is made for the benefit of, and may be
relied upon by, Andrews & Kurth L.L.P., as counsel to the Company, the
Placement Agent, Kramer, Levin, Naftalis & Frankel, as counsel to the Placement
Agent, and each of the Purchasers.

                  IN WITNESS WHEREOF, I have executed this certificate on this
_____ day of February, 1999.


                             -------------------------------------
                             Name: Geoffrey F. Cox
                             Title: Chief Executive Officer



                                      A-i

<PAGE>   31
                                                                      EXHIBIT B

                          ARONEX PHARMACEUTICALS, INC.

                            SECRETARY'S CERTIFICATE

                  I, Terance A. Murnane, certify that I am the duly elected,
qualified and acting Secretary of Aronex Pharmaceuticals, Inc., Inc., a
Delaware corporation (the "Company"), and as such, I am duly authorized to
execute this Certificate on behalf of the Company, and that I am familiar with
the facts certified below. All capitalized terms used herein but not otherwise
defined herein shall the meanings ascribed to such terms in the Placement
Agency Agreement dated as of November 19, 1998 between the Company and
Paramount Capital, Inc. (the "Placement Agency Agreement"). Reference is made
herein to the closing held on February , 1999 (the "Closing Date"). In
connection with the offering and sale of 6,000,000 shares of Common Stock (the
"Offering Quantity") of the Company, par value $.001 per share (the "Common
Stock"), pursuant to the registration statement on Form S-1 File No. 333-67599
(the "Registration Statement"), for which Paramount Capital, Inc. (the
"Placement Agent") has acted as Placement Agent, I do hereby further certify as
follows:

                  1. Attached hereto as Annex A is a true, correct and complete
copy of the Company's Certificate of Incorporation, as amended as in full force
and effect on the Closing Date. No amendment to such certificate has been
approved by the Board of Directors or stockholders of the Company or filed with
the Delaware Secretary of State since______ __, 1998. There are no proceedings
or actions have been taken by the Board of Directors or the Stockholders of the
Company in contemplation of any amendment to the Company's Certificate of
Incorporation or in contemplation of the merger, liquidation, consolidation, or
sale of all or substantially all of the assets or business of the Company or
which would otherwise threaten or impair the Company's corporate existence.

                  2. Attached hereto as Annex B is a true, correct and complete
copy of the Bylaws of the Company, as in full force and effect on the Closing
Date and at all times from November 19, 1998 through the Closing Date. No
action has been taken by the Board of Directors or the stockholders of the
Company in contemplation of any amendment to such Bylaws of the Company.

                  3. Attached hereto as Annex C is a true, correct and complete
copy of resolutions duly adopted by the Board of Directors by unanimous written
consent dated October 23, 1998 and February , 1999, and at the meeting of the
Board of Directors on December ___, 1998, and by the Pricing Committee of the
Board of Directors on February __, 1999. Such resolutions are the only
resolutions in effect adopted by the Board of Directors of the Company or any
committee thereof with respect to the Offering of the Shares and the
transactions contemplated by the Placement


                                      B-i

<PAGE>   32





Agency Agreement, and which have not been revoked, modified and amended or
rescinded and are in full force and effect on the Closing Date.


                  4. As of the Closing Date, each of the Offering Documents is
in the form authorized by the Board of Directors of the Company pursuant to the
resolutions set forth in Annex C.

                  5. Attached hereto as Annex D are true, correct and complete
copies of specimens of the certificates representing the Common Stock
heretofore approved and adopted by the Board of Directors of the Company. Each
of the certificates representing Common Stock delivered on the Closing Date to
each of the Purchasers has been executed by the genuine or facsimile signature
of officers of the Company who have been duly elected or appointed, qualified
and acting as such officers on the date such certificates were executed and
delivered, all in accordance with the Certificate and By-laws of the Company
and the requirements of applicable law.

                  6. Attached hereto as Annex E is a true, correct and complete
copy of the form of Placement Warrants heretofore approved and adopted by the
Board of Directors of the Company. Each of the Placement Warrants delivered on
the Closing Date pursuant to the Placement Agency Agreement has been executed
by the genuine or facsimile signature of officers of the Company who have been
duly elected or appointed, qualified and acting as such officers on the date
such certificates were executed and delivered, all in accordance with the
Certificate and By-laws of the Company and the requirements of applicable law.

                  6. The minute books and records of the Company, relating to
all proceedings of the stockholders, the Board of Directors of the Company and
the Compensation Committee, the Audit Committee and the Nominating Committee of
such Board have been made available to Kramer, Levin, Naftalis & Frankel,
counsel to the Placement Agent, and, in such form, are the original minute
books and records of the Company. There have been no material changes,
alterations or additions in such minutes or records since their examination by
Kramer, Levin, Naftalis & Frankel on behalf of the Placement Agent.

                  7. Attached as Annex F hereto are true and correct copies of
all correspondence and other written communications and all memoranda
evidencing any oral communications between any directors, officers, employees,
accountants, counsel or other representatives of the Company on the one hand
and any members of the staff of the Commission on the other hand in connection
with the Registration Statement. Neither the Company nor any of its directors,
officers, employees, accountants, counsel or other representatives has received
any written or oral comments from any member of the staff of the Commission
with respect to the Registration Statement other than those heretofore
communicated to counsel for the Placement Agent.



                                      B-ii

<PAGE>   33





                  8. Each person who, as an officer or director of the Company,
signed any of the Offering Documents or any other document in connection with
the offering and sale of the Common Stock, the Placement Warrants and the
closing relating thereto was duly elected or appointed, qualified and acting as
such officer or director at the respective times of the signing and delivery
thereof and was duly authorized to sign such document on behalf of the Company,
and the signature of each such person appearing on each such document is the
genuine signature of such officer, director or person duly appointed for the
purpose of executing such documents under valid powers of attorney, and each
individual who signed such signature pages, personally or by an
attorney-in-fact, was then duly elected, qualified and acting as an officer or
director of the Company as stated therein.

                  9. The following persons are, and have been at all times
since a date prior to November 19, 1998, duly qualified and acting officers of
the Company, duly elected or appointed to the offices set forth opposite their
respective names, and the signature opposite the name of each such officer is
his or her, or a facsimile of his or her, authentic signature:

<TABLE>
<CAPTION>

         Name                               Office                              Signature
         ----                               ------                              ---------
<S>                                         <C>                                <C>
         Geoffrey F. Cox                    Chairman, Chief                     ------------------
                                            Executive Officer

         Terance A. Murnane                 Secretary                           ------------------

</TABLE>

                  This certificate is made for the benefit of, and may be
relied upon by, Andrews & Kurth L.L.P., counsel to the Company, the Placement
Agent, Kramer, Levin, Naftalis & Frankel, as counsel to the Placement Agent,
and each of the Purchasers.



                  IN WITNESS WHEREOF, I have hereunto set forth my hand this ___
day of February, 1999.

         [SEAL]

                             ----------------------------------
                             Name:    Terance A. Murnane
                             Title:   Secretary



                                     B-iii

<PAGE>   34






                  I, Geoffrey F. Cox, Chief Executive Officer of the Company,
do hereby certify that Terance A. Murnane whose genuine signature appears
above, is, and has been at all times since November 19, 1998, the duly elected
or appointed, qualified and acting Secretary of the Company.

                  IN WITNESS WHEREOF, I have hereunto set forth my hand this
___ day of February , 1999.


                             -------------------------------------
                             Name:   Geoffrey F. Cox
                             Title:  Chief Executive Officer



                                      B-iv

<PAGE>   35





                                                                      EXHIBIT C

THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR
INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, OR ANY STATE SECURITIES LAW. SUCH SECURITIES MAY NOT BE SOLD OR
TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR UNLESS SUCH SALE OR TRANSFER
IS EXEMPT FROM THE REGISTRATION AND PROSPECTUS DELIVERY REQUIREMENTS OF SAID
ACT.



                          ARONEX PHARMACEUTICALS, INC.



                     WARRANT FOR THE PURCHASE OF SHARES OF
                                  COMMON STOCK

No. CW- [ ]                                                          [ ] Shares


                  FOR VALUE RECEIVED, ARONEX PHARMACEUTICALS, INC., a Delaware
corporation (the "COMPANY"), hereby certifies that [NAME], or its permitted
registered assigns is entitled to purchase from the Company, at any time or
from time to time commencing on [INSERT DATE THAT IS ONE YEAR FROM THE
EFFECTIVE DATE], 2000 and prior to 5:00 P.M., New York City time, on [INSERT
DATE THAT IS FIVE YEARS FROM THE EFFECTIVE DATE], 2004 [INSERT NUMBER OF
SHARES] (_______) fully paid and non-assessable shares of common stock, $.001
par value per share, of the Company for an aggregate purchase price of
$_______. (Hereinafter, (i) said common stock, $.001 par value per share, of
the Company, is referred to as the "COMMON STOCK", (ii) the shares of the
Common Stock purchasable hereunder or under any other Warrant (as hereinafter
defined) are referred to as the "WARRANT SHARES", (iii) the aggregate purchase
price payable for the Warrant Shares purchasable hereunder is referred to as
the "AGGREGATE WARRANT PRICE", (iv) the price payable (initially $______ per
share, subject to adjustment) for each of the Warrant Shares hereunder is
referred to as the "PER SHARE WARRANT PRICE", (v) this Warrant, all similar
Warrants issued on the date hereof and all warrants hereafter issued in
exchange or substitution for this Warrant or such similar Warrants are referred
to as the "WARRANTS", (vi) the holder of this Warrant is referred to as the
"HOLDER" and the holder of this Warrant and all other Warrants and Warrant
Shares are referred to as the "HOLDERS" and Holders of more than fifty percent
(50%) of the outstanding Warrants and Warrant Shares are referred to as the
"MAJORITY OF THE HOLDERS") and (vii) the then Current Market Price per share of
the Common Stock (the "CURRENT MARKET PRICE") shall be deemed to be the last
sale price of the Common Stock on




                                      C-i

<PAGE>   36





the trading day prior to such date or, in case no such reported sales take
place on such day, the average of the last reported bid and asked prices of the
Common Stock on such day, in either case on the principal national securities
exchange on which the Common Stock is admitted to trading or listed, or if not
listed or admitted to trading on any such exchange, the representative closing
sale price of the Common Stock as reported by the National Association of
Securities Dealers, Inc. Automated Quotations System ("NASDAQ"), or other
similar organization if NASDAQ is no longer reporting such information, or, if
the Common Stock is not reported on NASDAQ, the high per share sale price for
the Common Stock in the over-the-counter market as reported by the National
Quotation Bureau or similar organization, or if not so available, the fair
market value of the Common Stock as determined in good faith by the Board of
Directors. The Aggregate Warrant Price is not subject to adjustment. The Per
Share Warrant Price is subject to adjustment as hereinafter provided; in the
event of any such adjustment, the number of Warrant Shares deliverable upon
exercise of this Warrant shall be adjusted by dividing the Aggregate Warrant
Price by the Per Share Warrant Price in effect immediately after such
adjustment.

                  This Warrant, together with Warrants of like tenor,
constituting in the aggregate Warrants to purchase [INSERT NUMBER OF SHARES]
Warrant Shares, was originally issued pursuant to an agency agreement between
the Company and Paramount Capital, Inc., as placement agent (the "PLACEMENT
AGENT") in connection with the offering (the "OFFERING") of 6,000,000 shares
(the "SHARES").

                  1.   EXERCISE OF WARRANT.

                  (a)  This Warrant may be exercised in whole at any time, or in
part from time to time, commencing on [INSERT DATE THAT IS 12 MONTHS FROM THE
EFFECTIVE DATE], 2000 and prior to 5:00 P.M., New York City time, on [INSERT
DATE THAT IS FIVE YEARS FROM THE EFFECTIVE DATE], 2004 by the Holder:

                           (i) by the surrender of this Warrant (with the
subscription form at the end hereof duly executed) at the address set forth in
Section 10(a) hereof, together with proper payment of the Aggregate Warrant
Price, or the proportionate part thereof if this Warrant is exercised in part,
with payment for the Warrant Shares made by certified or official bank check
payable to the order of the Company; or

                           (ii) on any date on which the Current Market Price
exceeds the Per Share Warrant Price, by the surrender of this Warrant (with the
cashless exercise form at the end hereof duly executed) (a "CASHLESS EXERCISE")
at the address set forth in Section 10(a) hereof. Such presentation and
surrender shall be deemed a release of the Company's obligation to issue
additional Warrant Shares pursuant to this Warrant and waiver of the Company's
right to require Holder to pay the Aggregate Warrant Price, or the
proportionate part thereof if this Warrant is exercised in part. In the event
of a Cashless Exercise, the Holder shall exchange its Warrant for that number
of




                                      C-ii

<PAGE>   37





Warrant Shares subject to such Cashless Exercise multiplied by a fraction, the
numerator of which shall be the excess of the then Current Market Price over
the then Per Share Warrant Price, and the denominator of which shall be the
then Current Market Price. For purposes of any computation under this Section
1(a), the then Current Market Price shall be based on the trading day prior to
the Cashless Exercise. Notwithstanding the foregoing, the Company shall have no
obligation to issue Warrant Shares for a consideration less than the aggregate
par value of the Warrant Shares then issued.

                  (b) If this Warrant is exercised in part, this Warrant must
be exercised for a number of whole shares of the Common Stock and the Holder is
entitled to receive a new Warrant covering the Warrant Shares that have not
been exercised and setting forth the proportionate part of the Aggregate
Warrant Price applicable to such Warrant Shares. Upon surrender of this
Warrant, the Company will (i) issue a certificate or certificates in the name
of the Holder for the largest number of whole shares of the Common Stock to
which the Holder shall be entitled and, if this Warrant is exercised in whole,
in lieu of any fractional share of the Common Stock to which the Holder shall
be entitled, pay to the Holder cash in an amount equal to the fair value of
such fractional share (determined in such reasonable manner as the Board of
Directors of the Company shall determine), and (ii) deliver the other
securities and properties receivable upon the exercise of this Warrant, or the
proportionate part thereof if this Warrant is exercised in part, pursuant to
the provisions of this Warrant.

                  2.       RESERVATION OF WARRANT SHARES; LISTING.

                  The Company agrees that, prior to the expiration of this
Warrant, the Company shall at all times have authorized and in reserve, and
shall keep available, solely for issuance and delivery upon the exercise of
this Warrant, the shares of the Common Stock and other securities and
properties as from time to time shall be receivable upon the exercise of this
Warrant, free and clear of all restrictions on sale or transfer, other than
under Federal or state securities laws, and free and clear of all preemptive
rights and rights of first refusal and use its reasonable best efforts to keep
the Warrant Shares authorized for listing on the Nasdaq National Market or, if
the Common Stock is no longer traded there, the Nasdaq SmallCap Market, any
national securities exchange, or other trading market on which the Common Stock
trades, upon notice of issuance.

                  3.       PROTECTION AGAINST DILUTION.

                  (a) If, at any time or from time to time after the date of
this Warrant, the Company shall (i) subdivide its outstanding shares of Common
Stock into a greater number of shares (whether by stock dividend or stock
split) or (ii) combine its outstanding shares of Common Stock into a smaller
number of shares, the Per Share Warrant Price shall be adjusted to be equal to
a fraction, the numerator of which shall be the Aggregate Warrant Price and the
denominator of which shall be the number of shares of Common Stock or other
capital stock of the Company that the




                                     C-iii

<PAGE>   38





Holder would have owned immediately following such action had such Warrant been
exercised immediately prior thereto. An adjustment made pursuant to this
Subsection 3(a) shall become effective immediately after the record date in the
case of a dividend or distribution, and shall become effective immediately
after the effective date in the case of a subdivision or combination.

                  (b) In case of any capital reorganization or
reclassification, or any consolidation or merger to which the Company is a
party other than a merger or consolidation in which the Company is the
continuing corporation, or in case of any sale or conveyance to another entity
of the property of the Company as an entirety or substantially as a entirety,
or in the case of any statutory exchange of securities with another corporation
(including any exchange effected in connection with a merger of a third
corporation into the Company), the Holder of this Warrant shall have the right
thereafter to receive on the exercise of this Warrant the kind and amount of
securities, cash or other property which the Holder would have owned or have
been entitled to receive immediately after such reorganization,
reclassification, consolidation, merger, statutory exchange, sale or conveyance
had this Warrant been exercised immediately prior to the effective date of such
reorganization, reclassification, consolidation, merger, statutory exchange,
sale or conveyance and in any such case, if necessary, appropriate adjustment
shall be made in the application of the provisions set forth in this Section 3
with respect to the rights and interests thereafter of the Holder of this
Warrant to the end that the provisions set forth in this Section 3 shall
thereafter correspondingly be made applicable, as nearly as may reasonably be,
in relation to any shares of stock or other securities or property thereafter
deliverable on the exercise of this Warrant. The above provisions of this
Section 3(b) shall similarly apply to successive reorganizations,
reclassifications, consolidations, mergers, statutory exchanges, sales or
conveyances. The Company shall require the issuer of any shares of stock or
other securities or property thereafter deliverable on the exercise of this
Warrant to be responsible for all of the agreements and obligations of the
Company hereunder. Notice of any such reorganization, reclassification,
consolidation, merger, statutory exchange, sale or conveyance and of said
provisions so proposed to be made, shall be mailed to the Holders of the
Warrants not less than twenty (20) days prior to such event. A sale of all or
substantially all of the assets of the Company for a consideration consisting
primarily of securities shall be deemed a consolidation or merger for the
foregoing purposes.

                  (c) Whenever the Per Share Warrant Price is adjusted as
provided in this Section 3 and upon any modification of the rights of a Holder
of Warrants in accordance with this Section 3, the Company shall promptly
prepare a brief statement of the facts requiring such adjustment or
modification and the manner of computing the same and cause copies of such
certificate to be mailed to the Holders of the Warrants. The Company may, but
shall not be obligated to unless requested by a Majority of the Holders,
obtain, at its expense, a certificate of a firm of independent public
accountants of recognized standing selected by the Board of Directors (who may
be the regular auditors of the Company) setting forth the Per Share Warrant
Price and the number of Warrant Shares in effect after such adjustment or the
effect of such modification, a brief statement of the facts




                                      C-iv

<PAGE>   39





requiring such adjustment or modification and the manner of computing the same
and cause copies of such certificate to be mailed to the Holders of the
Warrants.

                  4. FULLY PAID STOCK; TAXES. The shares of the Common Stock
represented by each and every certificate for Warrant Shares delivered on the
exercise of this Warrant shall at the time of such delivery, be duly
authorized, validly issued and outstanding, fully paid and nonassessable, and
not subject to preemptive rights or rights of first refusal, and the Company
will take all such actions as may be necessary to assure that the par value, if
any, per share of the Common Stock is at all times equal to or less than the
then Per Share Warrant Price. The Company shall pay, when due and payable, any
and all Federal and state stamp, original issue or similar taxes which may be
payable in respect of the issue of any Warrant Share or any certificate thereof
to the extent required because of the issuance by the Company of such security.
The Company will not, however, be required to pay any such taxes imposed in
connection with any transfer of this Warrant or any Warrant Shares or any
federal or state income taxes payable in respect of the purchase, ownership,
sale, transfer, exercise or other disposition of this Warrant or any Warrant
Shares.

                  5. REGISTRATION UNDER SECURITIES ACT OF 1933, AS AMENDED. (a)
As used in this Section 5 of this Warrant, the following terms shall have the
following meanings:

                           (i) "Closing Date" shall mean the date on which this
Warrant was issued.

                           (ii) "Effective Date" shall mean the date on which
the registration statement filed in connection with the Offering was declared
effective by the SEC.

                           (iii) "Holder" shall mean the Person in whose name
the Warrant is registered and any Person holding Registrable Securities to whom
the rights under this Section 5 have been transferred in accordance with
Section 5(k) hereof.

                           (iv) "Person" shall mean any person, individual,
corporation, partnership, trust or other nongovernmental entity or any
governmental agency, court, authority or other body (whether foreign, federal,
state, local or otherwise).

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

                           (vi) "Registrable Securities" shall mean the shares
of Common Stock issuable upon exercise of the Warrants; provided, however, that
securities shall only be treated as Registrable Securities if and only for so
long as they (A) have not been disposed of pursuant to a registration statement
declared effective by the SEC, (B) have not been sold in a transaction exempt
from the registration and prospectus delivery requirements of the Securities
Act so that all transfer




                                      C-v

<PAGE>   40





restrictions and restrictive legends with respect thereto are removed upon the
consummation of such sale, (C) may not be sold by the Holder or a permitted
transferee under Rule 144(k) under the Securities Act (or other exemption from
registration acceptable to the Company) and (D) are held by a Holder (whether
the original Holder or a Holder that is a permitted transferee pursuant to
Section 5(k)).

                           (vii) "Registration Expenses" shall mean all
expenses incurred by the Company in complying with Sections 5(b) and 5(c)
hereof, including, without limitation, all registration, qualification and
filing fees, printing expenses, escrow fees, fees and expenses of counsel for
the Company, blue sky fees and expenses and the expense of any special audits
incident to or required by any such registration (but excluding selling
commissions or fees of legal counsel for any Holder).

                           (viii) "Registration Period" shall have the meaning
ascribed to such term in Section 5(d).

                           (ix) "Rule 144" shall mean Rule 144 promulgated by
the SEC under the Securities Act.

                           (x) "Securities Act" shall mean the Securities Act
of 1933, as amended.

                           (xi) "SEC" shall mean the United States Securities
and Exchange Commission.

                           (xii) "Selling Expenses" shall mean all underwriting
discounts and selling commissions applicable to the sale of Registrable
Securities and all fees and expenses of legal counsel for any Holder.

                           (xiii) "Shelf Registration Statement" shall have the
meaning ascribed to such term in Section 5(b).

                  (b) Demand Registration Rights. (i) At any time after the
date that is twelve (12) months from the Effective Date, and continuing for a
period of five (5) years from the Effective Date, a Majority of the Holders may
on one (1) occasion demand that the Company (A) file with the SEC a shelf
registration statement under the Securities Act (a "Shelf Registration
Statement") with respect to the Registrable Securities and use its commercially
reasonable best efforts to have such Shelf Registration Statement declared
effective by the SEC and (B) use its commercially reasonable best efforts to
effect the registration, qualifications or compliances (including, without
limitation, the execution of any required undertaking to file post-effective
amendments, appropriate qualifications under applicable blue sky or other state
securities laws and appropriate compliance with applicable securities laws,
requirements or regulations) as may be so reasonably requested and




                                      C-vi

<PAGE>   41





as would permit or facilitate the sale and distribution of all Registrable
Securities. Notwithstanding the foregoing, the Company will not be obligated to
enter into any underwriting agreement for the sale of any of the Registrable
Securities.

                  (ii) Notwithstanding any other provision of this Warrant, the
Company shall not be required to take any of the actions with respect to a
Shelf Registration Statement to the extent that the Company is in possession of
material non-public information that it has a bona fide business purpose for
preserving as confidential and that is not then otherwise required to be
disclosed and it delivers written notice to each Holder that it intends to
defer the actions so required, and that such Holder may not make offers or
sales under a Shelf Registration Statement, for a period not to exceed sixty
(60) days from the date of such notice; provided, however, that the Company may
deliver only two such notices in the aggregate during any twelve-month period.

                  (c) Piggy-Back Registration Rights. (i) The Company agrees
that if, at any time, and from time to time, commencing on the date that is
nine (9) months from the Effective Date and ending on the date that is seven
(7) years from the Effective Date, the Board of Directors of the Company shall
authorize the filing of a registration statement under the Securities Act
(other than a registration statement on Form S-8, Form S-4 or any other form or
successor form that does not include substantially the same information as
would be required in a form for the general registration of securities) in
connection with the proposed offer of any of its securities by it or any of its
stockholders, the Company shall, (A) promptly notify the Holder that such
registration statement will be filed and that the Registrable Securities will
be included in such registration statement at the Holder's request, (B) cause
such registration statement to cover all such Registrable Securities for which
the Holder requests inclusion, (C) use its reasonable best efforts to cause
such registration statement to become effective as soon as practicable and (D)
take all other action necessary under any Federal or state law or regulation of
any governmental authority to permit all such Registrable Securities to be sold
or otherwise disposed of, and will maintain such compliance with each such
Federal and state law and regulation of any governmental authority for the
period necessary for the Holder to effect the proposed sale or other
disposition, but in no event greater than nine (9) months.

                           (ii) Notwithstanding any other provision in this
Warrant, other than with respect to a registration statement filed pursuant to
Section 5(b), the Company may at any time abandon or delay any registration
commenced by the Company. In the event of such an abandonment by the Company,
the Company shall not be required to continue registration of the Registrable
Securities requested by the Holder for inclusion and the Holder shall retain
the right to request inclusion of the Registrable Securities in accordance with
Section 5(c)(i).

                           (iii) Notwithstanding any other provision in this
Warrant, the rights of the Holder hereunder shall be subordinate to the rights
of a holder with registration rights under the Registration Rights Agreement
dated September 11, 1995 by Argus Pharmaceuticals, Inc. for the benefit of each
such Holder (as defined therein).




                                     C-vii

<PAGE>   42






                  (d) Obligations. Whenever required under this Warrant to
include Registrable Securities in a Company registration statement, the Company
shall, as expeditiously as reasonably possible:

                           (i) use its reasonable best efforts to keep such
registration, and any qualification, exemption or compliance under state
securities laws which the Company determines to obtain, continuously effective
until the Holders have completed the distribution described in the registration
statement relating thereto or nine (9) months, whichever is shorter. The period
of time during which the Company is required hereunder to keep the Registration
Statement effective is referred to herein as "the Registration Period."
Notwithstanding the foregoing, at the Company's election, the Company may cease
to keep such registration, qualification, exemption or compliance effective
with respect to any Registrable Securities, and the registration rights of the
Holder shall expire, at such time as the Holder may sell under Rule 144(k)
under the Securities Act (or other exemption from registration acceptable to
the Company) all Registrable Securities then held by such Holder; and

                           (ii) advise the Holders:

                                    (A) when such registration statement or any
amendment thereto has been filed with the SEC and when such registration
statement or any post-effective amendment thereto has become effective;

                                    (B) of any request by the SEC for
amendments or supplements to such registration statement or the prospectus
included therein or for additional information;

                                    (C) of the issuance by the SEC of any stop
order suspending the effectiveness of such registration statement or the
initiation of any proceedings for such purpose;

                                    (D) of the receipt by the Company of any
notification with respect to the suspension of the qualification of the
Registrable Securities included therein for sale in any jurisdiction or the
initiation or threatening of any proceeding for such purpose; and

                                    (E) of the happening of any event that
requires the making of any changes in such registration statement or the
prospectus so that, as of such date, the statements therein are not misleading
and do not omit to state a material fact required to be stated therein or
necessary to make the statements therein (in the case of the prospectus, in the
light of the circumstances under which they were made) not misleading;

                           (iii) make every reasonable effort to obtain the
withdrawal of any order suspending the effectiveness of any Registration
Statement at the earliest possible time;




                                     C-viii

<PAGE>   43





                           (iv) furnish to each Holder, without charge, at
least one copy of such registration statement and any post-effective amendment
thereto, including financial statements and schedules, and, if the Holder so
requests in writing, all exhibits (including those incorporated by reference)
in the form filed with the SEC;

                           (v) during the Registration Period, deliver to each
Holder, without charge, as many copies of the prospectus included in such
registration statement and any amendment or supplement thereto as such Holder
may reasonably request; and the Company consents to the use, consistent with
the provisions hereof, of the prospectus or any amendment or supplement thereto
by each of the selling Holders of Registrable Securities in connection with the
offering and sale of the Registrable Securities covered by the prospectus or
any amendment or supplement thereto. In addition, upon the reasonable request
of the Holder and subject in all cases to confidentiality protections
reasonably acceptable to the Company, the Company will meet with a Holder of
more than 10% of the Warrants or Warrant Shares, as the case may be, or a
representative thereof at the Company's headquarters to discuss all information
relevant for disclosure in such registration statement covering the Registrable
Securities, and will otherwise cooperate with any Holder conducting an
investigation for the purpose of reducing or eliminating such Holder's exposure
to liability under the Securities Act, including the reasonable production of
information at the Company's headquarters;

                           (vi) during the Registration Period, deliver to each
Holder, without charge, (A) as soon as practicable (but in the case of the
annual report of the Company to its stockholders, within 120 days after the end
of each fiscal year of the Company) one copy of: (1) its annual report to its
stockholders, if any (which annual report shall contain financial statements
audited in accordance with generally accepted accounting principles in the
United States of America by a firm of certified public accountants of
recognized standing); (2) if not included in substance in its annual report to
stockholders, its annual report on Form 10-K (or similar form); (3) each of its
quarterly reports to its stockholders, and, if not included in substance in its
quarterly reports to stockholders, its quarterly report on Form 10-Q (or
similar form), and (4) a copy of the full Registration Statement (the
foregoing, in each case, excluding exhibits); and (B) upon reasonable request,
all exhibits excluded by the parenthetical to the immediately preceding clause
(4), and all other information prepared by the Company that is generally
available to the public;

                           (vii) prior to any public offering of Registrable
Securities pursuant to any Registration Statement, register or qualify or
obtain an exemption for offer and sale under the securities or blue sky laws of
such jurisdictions as a Majority of the Holders reasonably requests in writing,
provided that the Company shall not for any such purpose be required to qualify
generally to transact business as a foreign corporation in any jurisdiction
where it is not so qualified or to consent to general service of process in any
such jurisdiction, and do any and all other acts or things reasonably necessary
or advisable to enable the offer and sale in such jurisdictions of the
Registrable Securities covered by such registration statement;




                                      C-ix

<PAGE>   44





                           (viii) cooperate with the Holders to facilitate the
timely preparation and delivery of certificates representing Registrable
Securities to be sold pursuant to any Registration Statement free of any
restrictive legends to the extent not required at such time and in such
denominations and registered in such names as Holders may request at least
three (3) business days prior to sales of Registrable Securities pursuant to
such registration statement;

                           (vix) upon the occurrence of any event contemplated
by Section 5(d)(ii)(E) above, the Company shall promptly prepare a
post-effective amendment to such registration statement or a supplement to the
related prospectus, or file any other required document so that, as thereafter
delivered to purchasers of the Registrable Securities included therein, the
prospectus will not include any untrue statement of a material fact or omit to
state any material fact necessary to make the statements therein, in the light
of the circumstances under which they were made, not misleading; and

                           (x) use its reasonable best efforts to comply with
all applicable rules and regulations of the SEC, and will make generally
available to the Holders not later than 45 days (or 90 days if the fiscal
quarter is the fourth fiscal quarter) after the end of its fiscal quarter in
which the first anniversary date of the effective date of such registration
statement occurs, an earnings statement satisfying the provisions of Section
11(a) of the Securities Act.

                  (e) Furnish Information. It shall be a condition precedent to
the obligation of the Company to take any action pursuant to this Warrant with
respect to the Registrable Securities of any selling Holder that such Holder
shall furnish to the Company such information regarding the Holder, the
Registrable Securities held by the Holder, and the intended method of
disposition of such securities as shall be reasonably required by the Company
to effect the registration of such Holder's Registrable Securities.

                  (f) Expenses of Company Registration. The Company shall bear
and pay all Registration Expenses incurred in connection with any registration,
filing or qualification of Registrable Securities with respect to the
registrations pursuant to Sections 5(b) and/or 5(c) for each Holder relating or
apportionable thereto, but excluding Selling Expenses. Notwithstanding the
foregoing, each Holder shall pay all registration expenses that such Holder is
required to pay under applicable law.

                  (g) Underwriting Requirements. In connection with any
offering involving an underwriting of shares of the Company's capital stock,
the Company shall not be required under Section 5(c) to include any Holder's
Registrable Securities in such underwriting unless such Holder accepts the
terms of the underwriting as agreed upon between the Company and the
underwriters selected by it (or by other persons entitled to select the
underwriters), and then only in such quantity as the underwriters determine in
their sole discretion will not jeopardize the success of the offering by the
Company. If the total amount of securities, including Registrable Securities,
requested by




                                      C-x

<PAGE>   45





stockholders to be included in such offering exceeds the amount of securities
sold other than by the Company that the underwriters determine in their sole
discretion is compatible with the success of the offering, then the Company
shall be required to include in the offering only that number of such
securities, including Registrable Securities, which the underwriters determine
in their sole discretion will not jeopardize the success of the offering (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 have been granted prior to the date of this Warrant or mutually
agreed to by such selling stockholders). For purposes of the preceding
parenthetical concerning apportionment, for any selling stockholder who is a
holder of Registrable Securities and is a partnership or corporation, the
partners, retired partners and stockholders 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; provided, the rights to
apportionment of the Holder and other holders of Registrable Securities
underlying the warrants (including this Warrant) granted pursuant to the
Placement Agency Agreement dated as of November 19, 1999 between the Company
and Paramount Capital, Inc. shall be superior to any rights to apportionment
that are granted by the Company after the date hereof and applicable to such
registration.

                  (h) 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 Warrant.

                  (i) Indemnification. In the event that any Registrable
Securities are included in a registration statement under this Warrant:

                           (i) To the extent permitted by law, the Company will
indemnify and hold harmless each Holder, any underwriter (as defined in the
Securities Act) for such Holder and each person, if any, who controls such
Holder or underwriter within the meaning of the Securities Act or the Exchange
Act, against any losses, claims, damages, or liabilities (joint or several) to
which they may become subject under the Securities Act, or the Exchange Act,
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"): (A) 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, (B) 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 (C) any violation
or alleged violation by the Company of the Securities Act, the Exchange Act, or
any rule or regulation promulgated under the Securities Act, or the Exchange
Act, and the Company will pay to each such




                                      C-xi

<PAGE>   46





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 Section 5(i) 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 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.

                           (ii) 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 Securities 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 Securities Act, or the Exchange
Act, 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 Section 5(i), in connection with
investigating or defending any such loss, claim, damage, liability, or action;
provided, however, that the indemnity agreement contained in this Section 5(i)
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 Section 5(i) exceed the gross proceeds
from the offering received by such Holder.

                           (iii) Promptly after receipt by an indemnified party
under this Section 5 of notice of the commencement of any action (including any
governmental action), such indemnified party shall, if a claim in respect
thereof is to be made against any indemnifying party under this Section 5,
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 notified, to assume the defense thereof with counsel selected
by the indemnifying party and approved by the indemnified party (whose approval
shall not be unreasonably withheld); provided, however, that an indemnified
party (together with all other indemnified parties which may be represented
without conflict by one counsel) shall have the right to retain one separate
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




                                     C-xii

<PAGE>   47





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 5, 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 5.

                           (iv) To the extent permitted by law, if the
indemnification provided for in this Section 5 is held by a court of competent
jurisdiction to be unavailable to an indemnified party with respect to any
loss, liability, claim, damage, or expense referred to therein, then the
indemnifying party, in lieu of indemnifying such indemnified party hereunder,
shall contribute to the amount paid or payable by such indemnified party as a
result of such loss, liability, claim, dam age, or expense in such proportion
as is appropriate to reflect the relative fault of the indemnifying party on
the one hand and of the indemnified party on the other in connection with the
statements or omissions that resulted in such loss, liability, claim, damage,
or expense as well as any other relevant equitable considerations. The relative
fault of the indemnifying party and of the indemnified party shall be
determined by reference to, among other things, whether the untrue or alleged
untrue statement of a material fact or the omission to state a material fact
relates to information supplied by the indemnifying party or by the
indemnified party and the parties' relative intent, knowledge, access to
information, and opportunity to correct or prevent such statement or omission.

                           (v) Notwithstanding the foregoing, to the extent
that the provisions on indemnification and contribution contained in the
underwriting agreement entered into in connection with the underwritten public
offering are in conflict with the foregoing provisions, the provisions in the
underwriting agreement shall control.

                           (vi) The obligations of the Company and Holders
under this Section 5 shall survive the completion of any offering of
Registrable Securities in a registration statement under this Warrant, and
otherwise.

                  (j) Reports Under Exchange Act. With a view to making
available to the Holders the benefits of Rule 144 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:

                           (i) make and keep public information available, as
those terms are understood and defined in Rule 144, at all times;

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





                                     C-xiii

<PAGE>   48





                           (iii) furnish to any Holder, so long as the Holder
owns any Registrable Securities, forthwith upon request (A) 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 (B) such other information as may be
reasonably requested in availing any Holder of any rule or regulation of the
SEC which permits the selling of any such securities without registration or
pursuant to such form.

                  (k) Permitted Transferees. The rights to cause the Company to
register Registrable Securities granted to the Holders by the Company under
this Warrant may be assigned in full by a Holder in connection with a transfer
by such Holder of its Registrable Securities if: (i) such Holder gives prior
written notice to the Company; (ii) such transferee agrees to comply with the
terms and provisions of this Warrant; (iii) such transfer is otherwise in
compliance with this Agreement and (iv) such transfer is otherwise effected in
accordance with applicable securities laws. Except as specifically permitted by
this Section 5(k), the rights of a Holder with respect to Registrable
Securities as set out herein shall not be transferable to any other Person, and
any attempted transfer shall cause all rights of such Holder therein to be
forfeited.

                  (l) Termination of Registration Rights. In addition, the
right of any Holder to request inclusion in any registration pursuant to
Sections 5(b) and 5(c) shall terminate if all shares of Registrable Securities
held by such Holder may immediately be sold under Rule 144.

                  7.  INVESTMENT INTENT; LIMITED TRANSFERABILITY.

                  (a) The Holder represents, by accepting this Warrant, that it
understands that this Warrant and any securities obtainable upon exercise of
this Warrant have not been registered for sale under Federal or state
securities laws and are being offered and sold to the Holder pursuant to one or
more exemptions from the registration requirements of such securities laws. In
the absence of an effective registration of such securities or an exemption
therefrom, any certificates for such securities shall bear the legend set forth
on the first page hereof. The Holder understands that it must bear the economic
risk of its investment in this Warrant and any securities obtainable upon
exercise of this Warrant for an indefinite period of time, as this Warrant and
such securities have not been registered under Federal or state securities laws
and therefore cannot be sold unless subsequently registered under such laws,
unless an exemption from such registration is available.

                  (b) The Holder, by its acceptance of this Warrant, represents
to the Company that it is acquiring this Warrant and will acquire any
securities obtainable upon exercise of this Warrant for its own account for
investment and not with a view to, or for sale in connection with, any
distribution thereof in violation of the Securities Act and that it is an
"accredited investor" within the meaning of Regulation D under the Securities
Act. The Holder agrees that this Warrant and any such securities will not be
sold or otherwise transferred unless (i) a registration statement with respect
to such transfer is effective under the Securities Act and any applicable state
securities laws or (ii) such sale or transfer is made pursuant to one or more
exemptions from the Securities Act.




                                     C-xiv

<PAGE>   49





                  (c) This Warrant may not be sold, transferred, assigned,
hypothecated or otherwise disposed of, directly or indirectly, for twelve (12)
months from the Effective Date except (i) to any firm or corporation that
succeeds to all or substantially all of the business of Paramount Capital,
Inc., (ii) to any of the officers of Paramount Capital, Inc., or of any such
successor firm, (iii) to any NASD member participating in the Offering or any
officer of such NASD member or (iv) in the case of an individual, pursuant to
such individual's last will and testament or the laws of descent and
distribution, and is so transferable only upon the books of the Company, which
the Company shall cause to be maintained for such purpose. The Company may
treat the registered Holder of this Warrant as it appears on the Company's
books at any time as the Holder for all purposes. The Company shall permit any
Holder of a Warrant or its duly authorized attorney, upon written request
during ordinary business hours, to inspect and copy or make extracts from its
books showing the registered Holders of Warrants. All Warrants issued upon the
transfer or assignment of this Warrant will be dated the same date as this
Warrant, and all rights of the holder thereof shall be identical to those of
the Holder.

                  8. LOSS, ETC., OF WARRANT. Upon receipt of evidence
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant, and of indemnity reasonably satisfactory to the Company, if lost,
stolen or destroyed, and upon surrender and cancellation of this Warrant, if
mutilated, the Company shall execute and deliver to the Holder a new Warrant of
like date, tenor and denomination.

                  9. WARRANT HOLDER NOT STOCKHOLDER. This Warrant does not
confer upon the Holder any right to vote on or consent to or receive notice as
a stockholder of the Company, as such, in respect of any matters whatsoever,
nor any other rights or liabilities as a stockholder, prior to the exercise
hereof; this Warrant does, however, require certain notices to Holders as set
forth herein.

                  10. COMMUNICATION. No notice or other communication under
this Warrant shall be effective unless, but any notice or other communication
shall be effective and shall be deemed to have been given if, the same is in
writing and is mailed by first-class mail, postage prepaid, addressed to:

                  (a) the Company at 8707 Technology Forest Place, The
         Woodlands, Texas 77381-1191, Attn: CEO or such other address as the
         Company has designated in writing to the Holder, or

                  (b) the Holder at c/o Paramount Capital, Inc., 787 Seventh
         Avenue, New York, NY 10019 or other such address as the Holder has
         designated in writing to the Company.

                  11. HEADINGS. The headings of this Warrant have been inserted
as a matter of convenience and shall not affect the construction hereof.





                                      C-xv

<PAGE>   50





                  12. APPLICABLE LAW. This Warrant shall be governed by and
construed in accordance with the law of the State of New York.

                  13. AMENDMENT, WAIVER, ETC. Except as expressly provided
herein, neither this Warrant nor any term hereof may be amended, waived,
discharged or terminated other than by a written instrument signed by the party
against whom enforcement of any such amendment, waiver, discharge or
termination is sought; provided, however, that any provisions hereof may be
amended, waived, discharged or terminated upon the written consent of the
Company and the Majority of the Holders.




                                     C-xvi

<PAGE>   51





                  IN WITNESS WHEREOF, the Company has caused this Warrant to be
signed by its Chief Executive Officer and has caused its corporate seal to be
hereunto affixed and attested by its Secretary this __th day of February, 1999.


                             ARONEX PHARMACEUTICALS, INC.



                             By:                                                
                                ---------------------------------
                             Name:   Geoffrey Cox
                             Title:  Chief Executive Officer and
                                     Chairman of the Board of Directors



ATTEST:



-----------------------------
Name:   Terance A. Murnane
Title:  Secretary

[Corporate Seal]





                                     C-xvii

<PAGE>   52





                              SUBSCRIPTION (CASH)

                      The undersigned, ___________________, pursuant to the
provisions of the foregoing Warrant, hereby agrees to subscribe for and
purchase ____________________ shares of the Common Stock, par value $.001 per
share, of Aronex Pharmaceuticals, Inc. covered by said Warrant, and makes
payment therefor in full at the price per share provided by said Warrant.


Dated:                                           Signature:                    
      -----------------                                    --------------------
                                                 Address:                      
                                                         ----------------------

                               CASHLESS EXERCISE

                      The undersigned ___________________, pursuant to the
provisions of the foregoing Warrant, hereby elects to exchange its Warrant for
___________________ shares of Common Stock, par value $.001 per share, of
Aronex Pharmaceuticals, Inc. pursuant to the Cashless Exercise provisions of
the Warrant.

Dated:                                           Signature:                    
      -----------------                                    --------------------
                                                 Address:                      
                                                         ----------------------

                                   ASSIGNMENT

                      FOR VALUE RECEIVED _______________ hereby sells, assigns
and transfers unto ____________________ the foregoing Warrant and all rights
evidenced thereby, and does irrevocably constitute and appoint
_____________________, attorney, to transfer said Warrant on the books of
Aronex Pharmaceuticals, Inc.

Dated:                                           Signature:                    
      ------------------                                   --------------------
                                                 Address:                      
                                                         ----------------------






                                    C-xviii

<PAGE>   53



                               PARTIAL ASSIGNMENT

                      FOR VALUE RECEIVED _______________ hereby assigns and
transfers unto ____________________ the right to purchase _______ shares of
Common Stock, par value $.001 per share, of Aronex Pharmaceuticals, Inc.
covered by the foregoing Warrant, and a proportionate part of said Warrant and
the rights evidenced thereby, and does irrevocably constitute and appoint
____________________, attorney, to transfer such part of said Warrant on the
books of Aronex Pharmaceuticals, Inc.

Dated:                                           Signature:                    
      --------------------                                 --------------------
                                                 Address:                      
                                                         ----------------------




                                     C-xix