Document:

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                                                                    EXHIBIT 4.1

                             SUBSCRIPTION AGREEMENT

         SUBSCRIPTION AGREEMENT (this "Agreement") made as of the date set forth
on the signature page hereof between Aronex Pharmaceuticals, Inc., a Delaware
corporation having a place of business at 8707 Technology Forest Place, The
Woodlands, Texas 77381 (the "Company") and the undersigned (the "Subscriber").

                              W I T N E S S E T H:

         WHEREAS, the Company has retained Paramount Capital, Inc. (the
"Finder") as Finder, on a "best efforts" basis, in a private placement offering
(the "Offering") of Units (the "Units") consisting of the Company's common
stock, par value $.001 per share (the "Common Stock"), and Warrants (as defined
below);

         WHEREAS, the Company desires to issue a number of Units with an
aggregate value of up to $10,000,000 (the "Offering Amount"), with each Unit
consisting of (i) a number of shares of Common Stock of the Company (rounded to
the nearest whole share, with one-half (0.5) of one share, or greater fraction
thereof, being rounded upward), determined by dividing one hundred thousand
dollars ($100,000) by $2.75, and (ii) a warrant (collectively, the "Warrants")
to purchase a number of shares of Common Stock equal to thirty-three percent
(33%) of the shares of Common Stock included in such Unit, such warrants to be
exercisable, in whole or in part, at any time prior to the fifth anniversary of
the date of issuance at an exercise price equal to $3.00 (the Common Stock, the
Warrants, and the Common Stock issuable upon the exercise of the Warrants are
sometimes herein collectively referred to as the "Securities") (the "Offering")
at a purchase price of $100,000 per Unit (the "Offering Price");

         WHEREAS, the Subscriber desires to purchase that number of Units set
forth on the signature page hereof on the terms and conditions hereinafter set
forth;

         NOW, THEREFORE, in consideration of the premises and the mutual
representations and covenants hereinafter set forth, the parties hereto do
hereby agree as follows:

I.     SUBSCRIPTION FOR UNITS AND REPRESENTATIONS BY SUBSCRIBER

         1.1 Subject to the terms and conditions hereinafter set forth, the
Subscriber hereby subscribes for and agrees to purchase from the Company such
number of Units and the Company agrees to sell such Units to the Subscriber as
is set forth upon the signature page hereof at a price equal to $100,000 per
Unit (the "Offering Price"). The purchase price is payable by personal or
business check, wire transfer of immediately available funds or money order made
payable to "State Street Bank & Trust Company, N.A., "Escrow Agent," F/B/O
Aronex

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Pharmaceuticals, Inc." contemporaneously with the execution and delivery
of this Agreement by the Subscriber.

                      All wires should be sent to:
                      State Street Bank & Trust Co.
                      Corporate Trust N.Y.
                      61 Broadway, 15th floor
                      New York, New York 10006
                        Account Number: [_________]
                  Reference Number: [_________]
                  ABA Routing Number: [_________]
                  For the account of: Aronex Pharmaceuticals, Inc.
                  By order of: [insert investor name]

The certificates representing the Common Stock and Warrants included in the
Units will be delivered by the Company within ten (10) days following the
consummation of the Offering as set forth in Article III hereof. The Subscriber
understands, however, that this purchase of the Units is contingent upon the
Company making sales of a minimum number of Units with an aggregate value of at
least $6,000,000 (the "Minimum Offering Amount"). As soon as practicable after
the Company receives subscriptions to purchase the Minimum Offering Amount, the
Company and the Finder shall use their reasonable best efforts to affect the
Closing (the "Initial Closing Date"). The Company may conduct additional
Closings from time to time until the entire Offering Amount is sold, but not
later than _______, 2000 (the "Final Closing Date").

         1.2 The Subscriber recognizes that the purchase of the Units involves a
high degree of risk including, but not limited to, the following: (i) the
Company remains a development stage business with limited operating history and
requires substantial funds in addition to the proceeds of the Offering; (ii) an
investment in the Company is highly speculative, and only investors who can
afford the loss of their entire investment should consider investing in the
Company and the Units; (iii) the Subscriber may not be able to liquidate his/its
investment; (iv) transferability of the Common Stock is extremely limited; (v)
in the event of a disposition of the Common Stock, the Subscriber could sustain
the loss of his/its entire investment and (vi) the Company has not paid any
dividends on its Common Stock since inception and does not anticipate the
payment of dividends in the foreseeable future.

         1.3 The Subscriber represents that the Subscriber is an "accredited
investor" as such term is defined in Rule 501 of Regulation D promulgated under
the Securities Act of 1933, as amended (the "Act"), as indicated by the
Subscriber's responses to the questions contained in Article VII hereof, and
that the Subscriber is able to bear the economic risk of an investment in the
Units.

         1.4 The Subscriber hereby acknowledges and represents that (i) the
Subscriber has prior investment experience, including investment in securities
which are non-listed, unregistered and/or not traded on the Nasdaq National or
SmallCap Market, a national stock exchange nor on the National Association of
Securities Dealers, Inc. (the "NASD") automated

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quotation system for actively traded stocks ("Nasdaq"), or the Subscriber has
employed the services of an investment advisor, attorney and/or accountant to
read all of the documents furnished or made available by the Company to the
Subscriber and to all other prospective investors in the Units and to evaluate
the merits and risks of such an investment on the Subscriber's behalf; (ii) the
Subscriber recognizes the highly speculative nature of this investment; and
(iii) the Subscriber is able to bear the economic risk which the Subscriber
hereby assumes.

         1.5 The Subscriber hereby acknowledges receipt and careful review of
this Agreement and all attachments to it, and hereby represents that the
Subscriber has been furnished by the Company during the course of this
transaction with all information regarding the Company which the Subscriber, its
investment advisor, attorney and/or accountant has requested or desired to know,
has been afforded the opportunity to ask questions of and receive answers from
duly authorized officers or other representatives of the Company concerning the
terms and conditions of the Offering, and has received any additional
information which the Subscriber has requested.

         1.6 (a) The Subscriber has relied solely upon the information provided
by the Company in this Agreement in making the decision to invest in the Units.
To the extent necessary, the Subscriber has retained, at his/its sole expense,
and relied upon appropriate professional advice regarding the investment, tax
and legal merits and consequences of this Agreement and its purchase of the
Units hereunder.

             (b) The Subscriber represents that no Units were offered or sold
to it by means of any form of general solicitation or general advertising,
and in connection therewith the Subscriber did not: (A) receive or review any
advertisement, article, notice or other communication published in a newspaper
or magazine or similar media or broadcast over television or radio whether
closed circuit, or generally available; or (B) attend any seminar meeting or
industry investor conference whose attendees were invited by any general
solicitation or general advertising.

         1.7 The Subscriber hereby represents that the Subscriber, either by
reason of the Subscriber's business or financial experience or the business or
financial experience of the Subscriber's professional advisors (who are
unaffiliated with, and who are not compensated by, the Company or any affiliate
or selling agent of the Company, including the Finder, directly or indirectly),
has the capacity to protect the Subscriber's own interests in connection with
the transaction contemplated hereby.

         1.8 The Subscriber hereby acknowledges that the offering of the Units
has not been reviewed by the United States Securities and Exchange Commission
(the "SEC" or the "Commission") or any state securities regulatory authority,
since the Offering is intended to be exempt from the registration requirements
of Section 5 of the Act pursuant to Regulation D promulgated under the Act. The
Subscriber shall not sell or otherwise transfer the Units, the Common Stock
included in the Units, the Warrants, or the Common Stock underlying the Warrants
included in the Units unless they are registered under the Act or unless an
exemption from such registration is available.

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         1.9 The Subscriber understands that the Units, the Common Stock
included in the Units, the Warrants, and the Common Stock underlying the
Warrants included in the Units have not been registered under the Act by reason
of a claimed exemption under the provisions of the Act which depends, in part,
upon the Subscriber's investment intention. In this connection, the Subscriber
hereby represents that the Subscriber is purchasing the Units for the
Subscriber's own account for investment and not with a view toward the resale or
distribution to others. The Subscriber, if an entity, also represents that it
was not formed for the purpose of purchasing the Units.

         1.10 The Subscriber understands that although there currently is a
public market for the Common Stock, Rule 144 promulgated under the Act ("Rule
144") requires, among other conditions, a one-year holding period prior to the
resale (in limited amounts) of securities acquired in a non-public offering
without having to satisfy the registration requirements under the Act. The
Subscriber understands and hereby acknowledges that the Company is under no
obligation to register any of the Units, the Common Stock included in the Units,
or the Common Stock underlying the Warrants included in the Units, under the Act
or any state securities or "blue sky" laws other than as set forth in Article V.
The Subscriber agrees to hold the Company and its directors, officers,
employees, controlling persons and agents (including the Finder and its
officers, directors, employees, counsel, controlling persons and agents) and
their respective heirs, representatives, successors and assigns harmless and to
indemnify them against all liabilities, costs and expenses incurred by them as a
result of (i) any misrepresentation made by the Subscriber contained in this
Agreement (including the Confidential Investor Questionnaire contained in
Article VII herein), (ii) any sale or distribution by the Subscriber in
violation of the Act or any applicable state securities or "blue sky" laws or
(iii) any untrue statement of a material fact made by the Subscriber and
contained herein.

         1.11 The Subscriber consents to the placement of a legend on any
certificate or other document evidencing the Common Stock included in the Units
or the Common Stock underlying the Warrants included in the Units, that such
Units, the Common Stock included in the Units, and the Common Stock underlying
the Warrants included in the Units, have not been registered under the Act or
any state securities or "blue sky" laws and setting forth or referring to the
restrictions on transferability and sale thereof contained in this Agreement.
The Subscriber is aware that the Company will make a notation in its appropriate
records with respect to the restrictions on the transferability of the Units,
the Common Stock included in the Units, the Warrants, and the Common Stock
underlying the Warrants included in the Units.

         1.12 The Subscriber understands that the Company will review this
Agreement and is hereby given authority by the Subscriber to call Subscriber's
bank or place of employment or otherwise review the financial standing of the
Subscriber; and it is further agreed that the Company reserves the unrestricted
right, without further documentation or agreement on the part of the Subscriber,
to reject or limit any subscription, to accept subscriptions for fractional
Units and to close the Offering to the Subscriber at any time.

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         1.13 The Subscriber hereby represents that the address of the
Subscriber furnished by Subscriber on the signature page hereof is the
Subscriber's principal residence if Subscriber is an individual or its principal
business address if it is a corporation or other entity.

         1.14 The Subscriber represents that the Subscriber has full power and
authority (corporate, statutory and otherwise) to execute and deliver this
Agreement and to purchase the Units. This Agreement constitutes the legal, valid
and binding obligation of the Subscriber, enforceable against the Subscriber in
accordance with its terms.

         1.15 If the Subscriber is a corporation, partnership, limited liability
company, trust, employee benefit plan, individual retirement account, Keogh
Plan, or other entity (a) it is authorized and qualified to become an investor
in the Company and the person signing this Agreement on behalf of such entity
has been duly authorized by such entity to do so and (b) it is duly organized,
validly existing and in good standing under the laws of the jurisdiction of its
organization.

         1.16 The Subscriber acknowledges that if he or she is a Registered
Representative of an NASD member firm, he or she must give such firm the notice
required by the NASD Rules of Fair Practice, receipt of which must be
acknowledged by such firm in Section 7.4 below.

II.    REPRESENTATIONS BY AND COVENANTS OF THE COMPANY

       The Company hereby represents and warrants to the Subscriber that:

         2.1 Organization, Good Standing and Qualification. The Company is a
corporation duly organized, validly existing and in good standing under the laws
of the State of Delaware and has full corporate power and authority to conduct
its business as currently conducted. The Company is duly qualified to do
business as a foreign corporation and is in good standing in the State of Texas.

         2.2 Capitalization. The authorized capital stock of the Company
consists of 40,000,000 shares of common stock, par value $.001 per share, of
which there were 22,853,782 shares issued and outstanding as of December 31,
1999, and 5,000,000 shares of Preferred Stock, $.001 par value per share, none
of which shares are issued and outstanding. All outstanding shares of Common
Stock are duly authorized, validly issued, fully paid and non-assessable, free
of any liens or encumbrances and are not subject to preemptive rights. As of
December 31, 1999, the Company had reserved 5,223,972 shares of Common Stock for
issuance to employees, directors and consultants pursuant to the Company's Stock
Option Plan, of which 723,764 shares have been issued pursuant to option
exercises, and 2,613,475 shares of Common Stock are subject to outstanding,
unexercised options. As of December 31, 1999, the Company had reserved 250,000
shares of Common Stock for issuance to employees pursuant to the Company's
Employee Stock Purchase Plan, of which 131,931 shares have been issued to
employees. In addition, the Company has granted the following, which are issued
and outstanding: (i) an option to purchase 100,000 shares of its Common Stock to
a former consultant of the Company; (ii) warrants to purchase 667,414 shares of
its Common Stock pursuant to financing transactions and

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(iii) $5,000,000 in contingent stock rights issued to stockholders of Triplex
Pharmaceuticals Corporation ("Triplex") pursuant to the Company's 1995 merger
with Triplex. Other than as set forth above, or as contemplated in this
Agreement, there are no other options, warrants, calls, rights, commitments or
agreements of any character to which the Company is a party or by which either
the Company is bound or obligating the Company to issue, deliver, sell,
repurchase or redeem, or cause to be issued, delivered, sold, repurchased or
redeemed, any shares of the capital stock of the Company or obligating the
Company to grant, extend or enter into any such option, warrant, call, right,
commitment or agreement.

         2.3 Issuance. The Units, the Common Stock included in the Units, the
Warrants and the Common Stock underlying the Warrants included in the Units,
have been duly and validly authorized and, when issued and paid for pursuant to
this Agreement, will be validly issued, fully paid and nonassessable.

         2.4 Authorization; Enforceability. The Company has all corporate right,
power and authority to enter into this Agreement and to consummate the
transactions contemplated hereby. All corporate action on the part of the
Company, its directors and stockholders necessary for the authorization,
execution, delivery and performance of this Agreement by the Company, the
authorization, sale, issuance and delivery of the Units contemplated herein and
the performance of the Company's obligations hereunder has been taken. This
Agreement has been duly executed and delivered by the Company and constitutes a
legal, valid and binding obligation of the Company, enforceable against the
Company in accordance with its terms, subject to laws of general application
relating to bankruptcy, insolvency and the relief of debtors and rules of law
governing specific performance, injunctive relief or other equitable remedies,
and to limitations of public policy. The issuance and sale of the Units
contemplated hereby will not give rise to any preemptive rights or rights of
first refusal on behalf of any person.

         2.5 No Conflict; Governmental and Other Consents.

              (a) The execution and delivery by the Company of this Agreement
and the consummation of the transactions contemplated hereby will not result in
the violation of any law, statute, rule, regulation, order, writ, injunction,
judgment or decree of any court or governmental authority to or by which the
Company is bound, or of any provision of the Certificate of Incorporation or
By-Laws of the Company, and will not conflict with, or result in a breach or
violation of, any of the terms or provisions of, or constitute (with due notice
or lapse of time or both) a default under, any lease, loan agreement, mortgage,
security agreement, trust indenture or other agreement or instrument to which
the Company is a party or by which it is bound or to which any of its properties
or assets is subject, nor result in the creation or imposition of any lien upon
any of the properties or assets of the Company.

              (b) No consent, approval, authorization or other order of any
governmental authority or other third-party is required to be obtained by the
Company in connection with the authorization, execution and delivery of this
Agreement or with the authorization, issue and sale of the Units, except such
filings as may be required to be made with

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the Commission, the NASD and the Nasdaq and with any state or foreign blue sky
or securities regulatory authority.

         2.6 Litigation. The Company knows of no pending or threatened legal or
governmental proceedings against the Company which could materially adversely
affect the business, property, financial condition, results of operations or
prospects of the Company.

         2.7 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 Exchange Act of 1934, as amended (the "Exchange Act"), have been duly
filed with the Commission, 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 any subsequently filed report, to the best of
the Company's knowledge, were complete and correct in all material respects as
of the dates at which the information was furnished, and contained (as of such
dates) no untrue statements of a material fact nor omitted to state any material
fact necessary in order to make the statements contained therein, in light of
the circumstances under which they were made, not misleading.

         2.8 Investment Company. The Company is not an "investment company"
within the meaning of such term under the Investment Company Act of 1940, as
amended, and the rules and regulations of the Commission thereunder.

III.   TERMS OF SUBSCRIPTION; LOCK-UP

         3.1 The Company shall issue a number of Units with an aggregate value
of up to $10,000,000 , with each Unit consisting of (i) a number of shares of
Common Stock of the Company (rounded to the nearest whole share, with one-half
(0.5) of one share, or greater fraction thereof, being rounded upward),
determined by dividing one hundred thousand dollars ($100,000) by $2.75, and
(ii) Warrants to purchase a number of shares of Common Stock equal to
thirty-three percent (33%) of the shares of Common Stock included in such Unit,
such warrants to be exercisable, in whole or in part, at any time prior to the
fifth anniversary of the date of issuance, at an exercise price equal to $3.00
to all of the subscribers, in an amount to each Subscriber as set forth on such
Subscriber's signature page hereto. The offering period shall terminate at
11:59 p.m. New York City time on March 30, 2000. The Units will be offered on a
"best efforts" basis. As soon as practicable following receipt by the Company of
at least the Minimum Offering Amount, the Company may conduct an initial Closing
(the "Initial Closing"). The Company may conduct additional Closings from time
to time until the entire Offering Amount is sold, but not later than _________
2000.

         3.2 The Company has retained the Finder to assist in the placement of
the Units. The Finder will receive certain compensation as a result of
investments made by Subscribers who purchase Units in the Offering.

         3.3 Pending the sale of the Units, all funds paid hereunder shall be
deposited by the Company in escrow with the Escrow Agent, having a branch at
61 Broadway, New York,

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New York. If the Company shall not have obtained subscriptions (including this
subscription) for purchases of the entire Offering on or before the Final
Closing Date, then this subscription shall be void and all funds paid hereunder
by the Subscriber shall be promptly returned to the Subscriber, with interest,
subject to Section 3.5 hereof.

         3.4 The Subscriber hereby authorizes and directs the Company to deliver
the Units to be issued to the Subscriber pursuant to this Agreement directly to
the Subscriber's account maintained by the Finder, if any, or, if no such
account exists, to the residential or business address indicated on the
signature page hereto.

         3.5 The Subscriber hereby authorizes and directs the Company to return
any funds for unaccepted subscriptions to the same account from which the funds
were drawn, including any customer account maintained with the Finder.

         3.6 The undersigned Subscriber hereby irrevocably agrees that the
Subscriber will not, without the prior written approval of the Company, offer,
sell, contract to sell, make any short sale (including, but not limited to, a
"short against the box"), pledge, or otherwise dispose of directly or
indirectly, any of the Units, the Common Stock included in the Units, the
Warrants, or the Common Stock underlying the Warrants included in the Units, for
a period beginning on the date hereof and ending on the date 90 days following
the closing of this Agreement (the "Lock-up Period"). The Subscriber understands
that the Company will rely upon the representations set forth in this Agreement
and understands that this Agreement is irrevocable and shall be binding on the
Subscriber and its successors and assigns. The undersigned agrees and consents
to the entry of stop transfer instructions with the Company's transfer agent
against the transfer of the Units, the Common Stock included in the Units, the
Warrants, or the Common Stock underlying the Warrants included in the Units,
except in compliance with this Agreement. Notwithstanding the foregoing, any
transfer of Units, the Common Stock included in the Units, the Warrants, or the
Common Stock underlying the Warrants included in the Units which either (i) will
not result in any change in beneficial ownership, including, but not limited to,
pro rata partnership distributions and transfers into trusts for the benefit of
the original holder, or (ii) constitute bona fide gifts of such shares, will not
require the Company's approval; provided, further that the transferee will be
subject to this lock up for the remainder of the Lock-up Period under this
Agreement.

IV.    CONDITIONS TO OBLIGATIONS OF THE SUBSCRIBERS

         4.1 The Subscribers' obligation to purchase the Units at the Initial
Closing or any subsequent Closing is subject to the fulfillment on or prior to
the Closing of the following conditions, which conditions may be waived at the
option of each Subscriber to the extent permitted by law:

              (a) Representations and Warranties Correct. The representations
and warranties made by the Company in Article II hereof shall be true and
correct in all material respects when made, and shall be true and correct in all
material respects on the Closing Date with the same force and effect as if they
had been made on and as of said date.

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              (b) Covenants. All covenants, agreements and conditions contained
in this Agreement to be performed by the Company on or prior to such purchase
shall have been performed or complied with in all material respects.

              (c) Listing. The Company will promptly file an Application for
Listing of Additional Securities with the Nasdaq National Market in accordance
with Regulation M under the Exchange Act and/or take any other necessary action
to enable the Common Stock to trade on the Nasdaq National Market.

              (d) No Legal Order Pending. There shall not then be in effect any
legal or other order enjoining or restraining the transactions contemplated by
this Agreement.

              (e) No Law Prohibiting or Restricting Such Sale. There shall not
be in effect any law, rule or regulation prohibiting or restricting such sale or
requiring any consent or approval of any person which shall not have been
obtained to issue the Units (except as otherwise provided in this Agreement).

              (f) Minimum Subscriptions. The Company shall have received binding
subscriptions for the Minimum Offering Amount.

              (g) Legal Opinion. At the Closing, counsel to the Company shall
have delivered to the Finder for the benefit of the Finder and the Subscribers,
a legal opinion to such effect with respect to legal matters relating to this
Agreement as the Finder may require.

V.     REGISTRATION RIGHTS

         5.1 As used in this Agreement, the following terms shall have the
following meanings:

              (a) "Affiliate" shall mean, with respect to any Person (as defined
below), any other Person controlling, controlled by or under direct or indirect
common control with such Person (for the purposes of this definition "control,"
when used with respect to any specified Person, shall mean the power to direct
the management and policies of such person, directly or indirectly, whether
through ownership of voting securities, by contract or otherwise; and the terms
"controlling" and "controlled" shall have meanings correlative to the
foregoing).

              (b) "Business Day" shall mean a day Monday through Friday on which
banks are generally open for business in New York.

              (c) "Holders" shall mean the Subscribers and any person holding
Registrable Securities (including, without limitation, the shares of Common
Stock issuable upon exercise of the warrants (the "Placement Warrants") to be
granted to the Finder and/or its designees pursuant to that certain Finders
Agreement between the Company and the Finder dated March __, 2000 or any person
to whom the rights under Article V have been transferred in accordance with
Section 5.9 hereof.

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

              (e) 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.

              (f) "Registrable Securities" shall mean (i) the Units; (ii) the
Common Stock included in the Units; (iii) the Warrants; (iv) the Common Stock
underlying the Warrants included in the Units; (v) the shares of Common Stock
issuable upon exercise of the Placement Warrants; and (vi) any shares of Common
Stock issued as (or issuable upon the conversion of any warrant, right or other
security which is issued as) a dividend or other distribution with respect to or
in replacement of the Units, the Common Stock included in the Units, the
Warrants, the Common Stock underlying the Warrants included in the Units, or the
Common Stock issued upon exercise of the Placement 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 Commission, (B) have not been sold in a
transaction exempt from the registration and prospectus delivery requirements of
the Act so that all transfer restrictions and restrictive legends with respect
thereto are removed upon the consummation of such sale, (C) are held by a Holder
or a permitted transferee pursuant to Section 5.9, or (D) have not become
eligible for sale pursuant to Rule 144(k) (or any successor thereto) under the
Securities Act.

              (g) "Registration Expenses" shall mean all expenses incurred by
the Company in complying with Section 5.2 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 the fees of legal counsel for any Holder).

              (h) "Registration Statement" shall have the meaning ascribed to
such term in Section 5.2.

              (i) "Registration Period" shall have the meaning ascribed to such
term in Section 5.4.

              (j) "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.

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         5.2 As soon as practicable following the Initial Closing Date, but no
later than 30 days after the Initial Closing Date (the "Outside Filing Date"),
the Company shall file a "shelf" registration statement on the appropriate form
(the "Registration Statement") with the Commission and use its 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 or exemptions under applicable blue sky
or other state securities laws and appropriate compliance with applicable
securities laws, requirements or regulations) prior to the date which is 90 days
after such filing. Notwithstanding the foregoing, the Company shall not be
obligated to enter into any underwriting agreement for the sale of any of the
Registrable Securities.

         5.3 All Registration Expenses incurred in connection with any
registration, qualification, exemption or compliance pursuant to Section 5.2
shall be borne by the Company. All Selling Expenses relating to the sale of
securities registered by or on behalf of Holders shall be borne by such Holders
pro rata on the basis of the number of securities so registered.

         5.4 In the case of the registration, qualification, exemption or
compliance effected by the Company pursuant to this Agreement, the Company
shall, upon reasonable request, inform each Holder as to the status of such
registration, qualification, exemption and compliance. At its expense the
Company shall:

              (a) use its 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. 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 a Holder shall expire, at such time as they are no
longer, by reason of Rule 144(k) of the Act (or other exemption from
registration acceptable to the Company) required to register for the sale
thereof; and

              (b) advise the Holders:

                   (i) when the Registration Statement or any amendment thereto
has been filed with the Commission and when the Registration Statement or any
post-effective amendment thereto has become effective;

                   (ii) of any request by the Commission for amendments or
supplements to the Registration Statement or the prospectus included therein or
for additional information;

                   (iii) of the issuance by the Commission of any stop order
suspending the effectiveness of the Registration Statement or the initiation of
any proceedings for such purpose;

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<PAGE>   12

                   (iv) 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

                   (v) of the happening of any event that requires the making of
any changes in the 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;

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

              (d) 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 Commission;

              (e) 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 or a representative thereof at the
Company's headquarters to discuss all information relevant for disclosure in the
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 Act,
including the reasonable production of information at the Company's
headquarters;

              (f) during the Registration Period, deliver to each Holder,
without charge, (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 the following documents, other than those
documents available via EDGAR: (A) 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); (B) if not
included in substance in its annual report to stockholders, its annual report on
Form 10-K (or similar form); (C) 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 (D) a
copy of the full Registration Statement (the foregoing, in each case, excluding
exhibits); and (ii) upon reasonable request, all exhibits excluded by the
parenthetical to the immediately preceding clause (D), and all other information
that is generally available to the public;

                                       12
<PAGE>   13

              (g) 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 any such Holders reasonably request 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;

              (h) 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;

              (i) upon the occurrence of any event contemplated by Section
5.4(b)(v) above, the Company shall promptly prepare a post-effective amendment
to the 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

              (j) use its best efforts to comply with all applicable rules and
regulations of the Commission, 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 the Registration Statement occurs, an earnings
statement satisfying the provisions of Section 11(a) of the Act.

         5.5 The Holders shall have no right to take any action to restrain,
enjoin or otherwise delay any registration pursuant to Section 5.2 hereof as a
result of any controversy that may arise with respect to the interpretation or
implementation of this Agreement.

         5.6 (a) To the extent permitted by law, the Company shall indemnify
each Holder, each underwriter of the Registrable Securities and each person
controlling such Holder within the meaning of Section 15 of the Act, with
respect to which any registration, qualification or compliance has been effected
pursuant to this Agreement, against all claims, losses, damages and liabilities
(or action in respect thereof), including any of the foregoing incurred in
settlement of any litigation, commenced or threatened (subject to Section 5.6(c)
below), arising out of or based on any untrue statement (or alleged untrue
statement) of a material fact contained in any registration statement,
prospectus or offering circular, or any amendment or supplement thereof,
incident to any such registration, qualification or compliance, or based on any
omission (or alleged omission) to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading, in
light of the circumstances in which they were made, and will reimburse each
Holder, each underwriter of the Registrable Securities and each person
controlling such Holder, for reasonable legal and other expenses reasonably
incurred in

                                       13
<PAGE>   14

connection with investigating or defending any such claim, loss, damage,
liability or action as incurred; provided that the Company will not be liable in
any such case to the extent that any untrue statement or omission or allegation
thereof is made in reliance upon and in conformity with written information
furnished to the Company by or on behalf of such Holder and stated to be
specifically for use in preparation of such registration statement, prospectus
or offering circular; provided, further, that the Company will not be liable in
any such case where the claim, loss, damage or liability arises out of or is
related to the failure of the Holder to comply with the covenants and agreements
contained in this Agreement respecting sales of Registrable Securities, and
except that the foregoing indemnity agreement is subject to the condition that,
insofar as it relates to any such untrue statement or alleged untrue statement
or omission or alleged omission made in the preliminary prospectus but
eliminated or remedied in (i) the amended prospectus on file with the Commission
at the time the registration statement becomes effective, (ii) in the amended
prospectus filed with the Commission pursuant to Rule 424(b), or (iii) in the
prospectus subject to completion under Rule 434 of the Act, which together meet
the requirements of Section 10(a) of the Act (the "Final Prospectus"), such
indemnity agreement shall not inure to the benefit of any such Holder, any such
underwriter or any such controlling person, if a copy of the Final Prospectus
furnished by the Company to the Holder for delivery was not furnished to the
person or entity asserting the loss, liability, claim or damage at or prior to
the time such furnishing is required by the Act and the Final Prospectus would
have cured the defect giving rise to such loss, liability, claim or damage.

              (b) Each Holder will severally, if Registrable Securities held by
such Holder are included in the securities as to which such registration,
qualification or compliance is being effected, indemnify the Company, each of
its directors and officers, each underwriter of the Registrable Securities and
each person who controls the Company within the meaning of Section 15 of the
Act, against all claims, losses, damages and liabilities (or actions in respect
thereof), including any of the foregoing incurred in settlement of any
litigation, commenced or threatened (subject to Section 5.6(c) below), arising
out of or based on any untrue statement (or alleged untrue statement) of a
material fact contained in any registration statement, prospectus or offering
circular, or any amendment or supplement thereof, incident to any such
registration, qualification or compliance, or based on any omission (or alleged
omission) to state therein a material fact required to be stated therein or
necessary to make the statements therein not misleading, in light of the
circumstances in which they were made, and will reimburse the Company, such
directors and officers, each underwriter of the Registrable Securities and each
person controlling the Company for reasonable legal and any other expenses
reasonably incurred in connection with investigating or defending any such
claim, loss, damage, liability or action as incurred, in each case to the
extent, but only to the extent, that such untrue statement or omission or
allegation thereof is made in reliance upon and in conformity with written
information furnished to the Company by or on behalf of the Holder and stated to
be specifically for use in preparation of such registration statement,
prospectus or offering circular; provided that the indemnity shall not apply to
the extent that such claim, loss, damage or liability results from the fact that
a current copy of the prospectus was not made available to the Holder and such
current copy of the prospectus would have cured the defect giving rise to such
loss, claim, damage or liability. Notwithstanding the foregoing, in no event
shall a Holder be liable for any such claims, losses, damages or liabilities in
excess of the proceeds received by such Holder in the offering, except in the
event of fraud by such Holder.

                                       14
<PAGE>   15

              (c) Each party entitled to indemnification under this Section 5.6
(the "Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom, provided that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or litigation, shall be
approved by the Indemnified Party (whose approval shall not unreasonably be
withheld), and the Indemnified Party may participate in such defense at such
Indemnified Party's expense, and provided further that the failure of any
Indemnified Party to give notice as provided herein shall not relieve the
Indemnifying Party of its obligations under this Agreement, unless such failure
is materially prejudicial to the Indemnifying Party in defending such claim or
litigation. An Indemnifying Party shall not be liable for any settlement of an
action or claim effected without its written consent (which consent will not be
unreasonably withheld).

              (d) If the indemnification provided for in this Section 5.6 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 thereunder, shall contribute to the amount paid or payable by such
Indemnified Party as a result of such loss, liability, claim, damage 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 which 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.

         5.7 (a) Each Holder agrees that, upon receipt of any notice from the
Company of the happening of any event requiring the preparation of a supplement
or amendment to a prospectus relating to Registrable Securities so that, as
thereafter delivered to the Holders, such prospectus shall not contain an 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, each
Holder will forthwith discontinue disposition of Registrable Securities pursuant
to the registration statement contemplated by Section 5.2 until its receipt of
copies of the supplemented or amended prospectus from the Company and, if so
directed by the Company, each Holder shall deliver to the Company all copies,
other than permanent file copies then in such Holder's possession, of the
prospectus covering such Registrable Securities current at the time of receipt
of such notice.

              (b) Each Holder shall suspend, upon request of the Company, any
disposition of Registrable Securities pursuant to the Registration Statement and
prospectus contemplated by Section 5.2 during (i) any period not to exceed two
30-day periods within any one 12-month period the Company requires in connection
with a primary underwritten offering

                                       15
<PAGE>   16

of equity securities and (ii) any period, not to exceed one 45-day period per
circumstance or development, when the Company determines in good faith that
offers and sales pursuant thereto should not be made by reason of the presence
of material undisclosed circumstances or developments with respect to which the
disclosure that would be required in such a prospectus is premature, would have
an adverse effect on the Company or is otherwise inadvisable.

              (c) As a condition to the inclusion of its Registrable Securities,
each Holder shall furnish to the Company such information regarding such Holder
and the distribution proposed by such Holder as the Company may request in
writing or as shall be required in connection with any registration,
qualification or compliance referred to in this Article V.

              (d) Each Holder hereby covenants with the Company (i) not to make
any sale of the Registrable Securities without effectively causing the
prospectus delivery requirements under the Act to be satisfied, and (ii) if such
Registrable Securities are to be sold by any method or in any transaction other
than on a national securities exchange, the Nasdaq National Market, the Nasdaq
Small Cap Market or in the over-the-counter market, in privately negotiated
transactions, or in a combination of such methods, to notify the Company at
least five (5) business days prior to the date on which the Holder first offers
to sell any such Registrable Securities.

              (e) Each Holder acknowledges and agrees that the Registrable
Securities sold pursuant to the Registration Statement described in this Section
are not transferable on the books of the Company unless the stock certificate
submitted to the transfer agent evidencing such Registrable Securities is
accompanied by a certificate reasonably satisfactory to the Company to the
effect that (i) the Registrable Securities have been sold in accordance with
such Registration Statement and (ii) the requirement of delivering a current
prospectus has been satisfied.

              (f) Each Holder agrees not to take any action with respect to any
distribution deemed to be made pursuant to such registration statement which
would constitute a violation of Regulation M under the Exchange Act or any other
applicable rule, regulation or law.

              (g) At the end of the period during which the Company is obligated
to keep the Registration Statement current and effective as described above, the
Holders of Registrable Securities included in the Registration Statement shall
discontinue sales of shares pursuant to such Registration Statement upon receipt
of notice from the Company of its intention to remove from registration the
shares covered by such Registration Statement which remain unsold, and such
Holders shall notify the Company of the number of shares registered which remain
unsold immediately upon receipt of such notice from the Company.

         5.8 With a view to making available to the Holders the benefits of
certain rules and regulations of the Commission which at any time permit the
sale of the Registrable Securities to the public without registration, the
Company shall use its reasonable best efforts to:

                                       16
<PAGE>   17

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

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

              (c) so long as a Holder owns any unregistered Registrable
Securities, furnish to such Holder, upon any reasonable request, a written
statement by the Company as to its compliance with Rule 144 under the Act, and
of the Exchange Act, a copy of the most recent annual or quarterly report of the
Company, and such other reports and documents of the Company as such Holder may
reasonably request in availing itself of any rule or regulation of the
Commission allowing a Holder to sell any such securities without registration.

         5.9 The rights to cause the Company to register Registrable Securities
granted to the Holders by the Company under Section 5.1 may be assigned in full
by a Holder in connection with a transfer by such Holder of its Registrable
Securities, provided, however, that (i) such transfer may otherwise be effected
in accordance with applicable securities laws; (ii) such Holder gives prior
written notice to the Company; and (iii) such transferee agrees to comply with
the terms and provisions of this Agreement, and such transfer is otherwise in
compliance with this Agreement. Except as specifically permitted by this Section
5.9, 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.

         5.10 With the written consent of the Company and the Holders holding at
least a majority of the Registrable Securities that are then outstanding, any
provision of this Article V may be waived (either generally or in a particular
instance, either retroactively or prospectively and either for a specified
period of time or indefinitely) or amended. Upon the effectuation of each such
waiver or amendment, the Company shall promptly give written notice thereof to
the Holders, if any, who have not previously received notice thereof or
consented thereto in writing.

         5.11 Except to the extent any delay is due to the failure of a Holder
to reasonably cooperate in providing to the Company such information as shall be
reasonably requested by the Company in writing for use in the Registration
Statement, if the Registration Statement is not filed with the SEC on or before
the Outside Filing Date, the Company shall be required to pay, as liquidated
damages and not as a penalty, to each Holder of Registerable Securities issued
in the Offering an amount in cash equal to one percent (1%) of the aggregate
Offering Price paid by such Holder for the Units issued to such Holder in the
Offering for each 30 day period after the Outside Filing Date that the
Registration Statement remains unfiled.

                                       17
<PAGE>   18

VI.  MISCELLANEOUS

         6.1 Any notice or other communication given hereunder shall be deemed
sufficient if in writing and sent by registered or certified mail, return
receipt requested, or delivered by hand against written receipt therefore,
addressed to Aronex Pharmaceuticals, Inc., 8707 Technology Forest Place, The
Woodlands, Texas 77381, Attn: Controller, and to the Subscriber at the
Subscriber's address indicated on the signature page of this Agreement. Notices
shall be deemed to have been given or delivered on the date of mailing, except
notices of change of address, which shall be deemed to have been given or
delivered when received.

         6.2 Except as provided in Section 5.10 above, this Agreement shall not
be changed, modified or amended except by a writing signed by the parties to be
charged, and this Agreement may not be discharged except by performance in
accordance with its terms or by a writing signed by the party to be charged.

         6.3 Subject to the provisions of Section 5.9 and 6.13, this Agreement
shall be binding upon and inure to the benefit of the parties hereto and to
their respective heirs, legal representatives, successors and assigns. This
Agreement sets forth the entire agreement and understanding between the parties
as to the subject matter hereof and merges and supersedes all prior discussions,
agreements and understandings of any and every nature among them.

         6.4 Upon the execution and delivery of this Agreement by the
Subscriber, this Agreement shall become a binding obligation of the Subscriber
with respect to the purchase of the Units as herein provided; subject, however,
to the right hereby reserved to the Company to enter into the same agreements
with other subscribers and to add and/or delete other persons as subscribers.

         6.5 NOTWITHSTANDING THE PLACE WHERE THIS AGREEMENT MAY BE EXECUTED BY
ANY OF THE PARTIES HERETO, THE PARTIES EXPRESSLY AGREE THAT ALL THE TERMS AND
PROVISIONS HEREOF SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAWS
OF THE STATE OF NEW YORK WITHOUT REGARD TO PRINCIPLES OF CONFLICTS OF LAW. IN
THE EVENT THAT A JUDICIAL PROCEEDING IS NECESSARY, THE EXCLUSIVE FORUMS FOR
RESOLVING DISPUTES ARISING OUT OF OR RELATING TO THIS AGREEMENT ARE EITHER THE
SUPREME COURT OF THE STATE OF NEW YORK IN AND FOR THE COUNTY OF NEW YORK OR THE
FEDERAL COURTS FOR SUCH STATE AND COUNTY, AND ALL RELATED APPELLATE COURTS, THE
PARTIES HEREBY IRREVOCABLY CONSENT TO THE JURISDICTION OF SUCH COURTS AND AGREE
TO SAID VENUE.

         6.6 In order to discourage frivolous claims the parties agree that
unless a claimant in any proceeding arising out of this Agreement succeeds in
establishing his claim and recovering a judgment against another party
(regardless of whether such claimant succeeds against one of the other parties
to the action), then the other party shall be entitled to recover from such
claimant all of its/their reasonable legal costs and expenses relating to such
proceeding and/or incurred in preparation therefore.

                                       18
<PAGE>   19

         6.7 The holding of any provision of this Agreement to be invalid or
unenforceable by a court of competent jurisdiction shall not affect any other
provision of this Agreement, which shall remain in full force and effect. If any
provision of this Agreement shall be declared by a court of competent
jurisdiction to be invalid, illegal or incapable of being enforced in whole or
in part, such provision shall be interpreted so as to remain enforceable to the
maximum extent permissible consistent with applicable law and the remaining
conditions and provisions or portions thereof shall nevertheless remain in full
force and effect and enforceable to the extent they are valid, legal and
enforceable, and no provisions shall be deemed dependent upon any other covenant
or provision unless so expressed herein.

         6.8 It is agreed that a waiver by either party of a breach of any
provision of this Agreement shall not operate, or be construed, as a waiver of
any subsequent breach by that same party.

         6.9 The parties agree to execute and deliver all such further
documents, agreements and instruments and take such other and further action as
may be necessary or appropriate to carry out the purposes and intent of this
Agreement.

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

         6.11 (a) The Subscribers severally agree not to issue any public
statement with respect to the Subscribers' investment or proposed investment in
the Company or the terms of any agreement or covenant between them and the
Company without the Company's prior written consent, except such disclosures as
may be required under applicable law or under any applicable order, rule or
regulation.

              (b) The Company agrees not to disclose the names, addresses or any
other information about the Subscribers, except as required by law; provided,
that the Company may use the name (but not the address) of the Subscriber in the
Registration Statement.

         6.12 (a) Each Subscriber severally represents and warrants that it has
not engaged, consented to nor authorized any broker, finder or intermediary to
act on its behalf, directly or indirectly, as a broker, finder or intermediary
in connection with the transactions contemplated by this Agreement. Each
Subscriber hereby severally agrees to indemnify and hold harmless the Company
from and against all fees, commissions or other payments owing to any such
person or firm acting on behalf of such Subscriber hereunder.

              (b) The Company has engaged, consented to and authorized the
Finder in connection with the transactions contemplated by this Agreement. The
Company shall pay the Finder a commission and reimburse the Finder's expenses in
accordance with the Finders Agreement, and the Company shall indemnify and hold
harmless the Subscribers from and against all fees, commissions or other
payments owing by the Company to the Finder or any other person or firm acting
on behalf of the Company hereunder.

                                       19
<PAGE>   20

         6.13 Nothing in this Agreement shall create or be deemed to create any
rights in any person or entity not a party to this Agreement, except (a) for the
holders of Registrable Securities and (b) for the Finder pursuant to Sections
1.6(a) and 6.12(b) hereof.

         6.14 The Company acknowledges and agrees that irreparable damage would
occur in the event that any of the provisions of Article V of this Agreement
were not performed in accordance with its specific terms or were otherwise
breached and that such damage would not be compensable in money damages and that
it would be extremely difficult or impracticable to measure the resultant
damages. Accordingly, any Subscriber shall be entitled to an injunction or
injunctions with respect to the provisions of this Agreement and to enforce
specifically the terms and provisions hereof, in addition to any other remedy to
which it may be entitled at law or in equity, and the Company expressly waives
any defense that a remedy in damages would be adequate and expressly waives any
requirement in an action for specific performance for the posting of a bond by
the Subscriber bringing such action.

VII. CONFIDENTIAL INVESTOR QUESTIONNAIRE

         7.1 The Subscriber represents and warrants that he, she or it comes
within one category marked below, and that for any category marked, he, she or
it has truthfully set forth, where applicable, the factual basis or reason the
Subscriber comes within that category. ALL INFORMATION IN RESPONSE TO THIS
SECTION WILL BE KEPT STRICTLY CONFIDENTIAL. The undersigned agrees to furnish
any additional information which the Company deems necessary in order to verify
the answers set forth below.

Category A        The undersigned is an individual (not a partnership,
          -----   corporation, etc.) whose individual net worth, or joint net
                  worth with his or her spouse, presently exceeds $1,000,000.

                           Explanation. In calculating net worth you may include
                           equity in personal property and real estate,
                           including your principal residence, cash, short-term
                           investments, stock and securities. Equity in personal
                           property and real estate should be based on the fair
                           market value of such property less debt secured by
                           such property.

Category B        The undersigned is an individual (not a partnership,
          -----   corporation, etc.) who had an income in excess of $200,000 in
                  each of the two most recent years, or joint income with his or
                  her spouse in excess of $300,000 in each of those years (in
                  each case including foreign income, tax exempt income and full
                  amount of capital gains and losses but excluding any income of
                  other family members and any unrealized capital appreciation)
                  and has a reasonable expectation of reaching the same income
                  level in the current year.

                                       20
<PAGE>   21

Category C        The undersigned is a director or executive officer of the
          -----   Company which is issuing and selling the Units.

Category D        The undersigned is a bank; a savings and loan association;
          -----   insurance company; registered investment company; registered
                  business development company; licensed small business
                  investment company ("SBIC"); or employee benefit plan within
                  the meaning of Title 1 of ERISA and (a) the investment
                  decision is made by a plan fiduciary which is either a bank,
                  savings and loan association, insurance company or registered
                  investment advisor, or (b) the plan has total assets in excess
                  of $5,000,000 or (c) is a self directed plan with investment
                  decisions made solely by persons that are accredited
                  investors. (describe entity)

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

Category E        The undersigned is a private business development company as
          -----   defined in section 202(a)(22) of the Investment Advisors Act
                  of 1940. (describe entity)

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

Category F        The undersigned is either a corporation, partnership,
          -----   Massachusetts business trust, or non-profit organization
                  within the meaning of Section 501(c)(3) of the Internal
                  Revenue Code, in each case not formed for the specific purpose
                  of acquiring the Units and with total assets in excess of
                  $5,000,000. (describe entity)

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

Category G       The undersigned is a trust with total assets in excess of
          -----  $5,000,000, not formed for the specific purpose of acquiring
                 the Units, where the purchase is directed by a "sophisticated
                 investor" as defined in Regulation 506(b)(2)(ii) under the
                 Act.

Category H       The undersigned is an entity (other than a trust) in which all
          -----  of the equity owners are "accredited investors" within one or
                 more of the above categories. If relying upon this Category
                 alone, each equity owner must complete a separate copy of this
                 Agreement. (describe entity)

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

Category I       The undersigned is not within any of the categories above and
          -----  is therefore not an accredited investor.

                                       21
<PAGE>   22

The undersigned agrees that the undersigned will notify the Company at any time
on or prior to the Closing Date in the event that the representations and
warranties in this Agreement shall cease to be true, accurate and complete.

         7.2      SUITABILITY (please answer each question)

(a) For an individual Subscriber, please describe your current employment,
including the company by which you are employed and its principal business:

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

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

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

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

(b) For an individual Subscriber, please describe any college or graduate
degrees held by you:

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

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

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

(c) For all Subscribers, please list types of prior investments:

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

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

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

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

(d) For all Subscribers, please state whether you have you participated in other
private placements before:

               YES_______                         NO_______

(e) If your answer to question (d) above was "YES", please indicate frequency of
such prior participation in private placements of:

<TABLE>
<CAPTION>

                    Public                    Private                  Public or Private
                    Companies                 Companies                Biotechnology Companies
                    ---------                 ---------                -----------------------
<S>                 <C>                       <C>                      <C>

Frequently
                    --------------------       --------------------      --------------------
Occasionally
                    --------------------       --------------------      --------------------
Never
                    --------------------       --------------------      --------------------
</TABLE>

                                       22
<PAGE>   23

(f) For individual Subscribers, do you expect your current level of income to
significantly decrease in the foreseeable future:

                           YES_______                         NO_______

(g) For trust, corporate, partnership and other institutional Subscribers, do
you expect your total assets to significantly decrease in the foreseeable
future:

                           YES_______                         NO_______

(h) For all Subscribers, do you have any other investments or contingent
liabilities which you reasonably anticipate could cause you to need sudden cash
requirements in excess of cash readily available to you:

                           YES_______                         NO_______

(i) For all Subscribers, are you familiar with the risk aspects and the
non-liquidity of investments such as the securities for which you seek to
subscribe?

                           YES_______                         NO_______

(j) For all Subscribers, do you understand that there is no guarantee of
financial return on this investment and that you run the risk of losing your
entire investment?

                           YES_______                         NO_______

         7.3      MANNER IN WHICH TITLE IS TO BE HELD. (circle one)

                             (a)    Individual Ownership
                             (b)    Community Property
                             (c)    Joint Tenant with Right of
                                    Survivorship (both parties
                                    must sign)
                             (d)    Partnership*
                             (e)    Tenants in Common
                             (f)    Company*
                             (g)    Trust*
                             (h)    Other

         *If Units are being subscribed for by an entity, the attached
Certificate of Signatory must also be completed.

                                       23
<PAGE>   24

         7.4 NASD AFFILIATION.

Are you affiliated or associated with an NASD member firm (please check one):

Yes _________              No __________

If Yes, please describe:

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

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

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

*If Subscriber is a Registered Representative with an NASD member firm, have the
following acknowledgment signed by the appropriate party:

The undersigned NASD member firm acknowledges receipt of the notice required by
Article 3, Sections 28(a) and (b) of the Rules of Fair Practice.

---------------------------------
Name of NASD Member Firm

By:
    ------------------------------
         Authorized Officer

Date:
      ----------------------------

         7.5 The undersigned is informed of the significance to the Company of
the foregoing representations and answers contained in the Confidential Investor
Questionnaire contained in this Section 7 and such answers have been provided
under the assumption that the Company will rely on them.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       24
<PAGE>   25

[SIGNATURE PAGE]

"PURCHASE PRICE" = _____________________  X $100,000 = $__________
                     Number of Units

-----------------------------------         -----------------------------------
Signature                                   Signature (if purchasing jointly)

-----------------------------------         -----------------------------------
Name Typed or Printed                       Name Typed or Printed

-----------------------------------         -----------------------------------
Entity Name                                 Entity Name

-----------------------------------         -----------------------------------
Address                                     Address

-----------------------------------         -----------------------------------
City, State and Zip Code                    City, State and Zip Code

-----------------------------------         -----------------------------------
Telephone-Business                          Telephone--Business

-----------------------------------         -----------------------------------
Telephone-Residence                         Telephone--Residence

-----------------------------------         -----------------------------------
Facsimile-Business                          Facsimile--Business

-----------------------------------         -----------------------------------
Facsimile-Residence                         Facsimile--Residence

-----------------------------------         -----------------------------------
Tax ID # or Social Security #               Tax ID # or Social Security #

Name in which securities should be issued:
                                          -------------------------------------
CHECK THE BOX MARKED YES IF YOU WOULD LIKE THE SECURITIES TO BE DELIVERED TO
YOUR ACCOUNT WITH PARAMOUNT CAPITAL, INC.
                  YES ___  NO ___

(IF YOU CHECK "NO", SECURITIES WILL BE DELIVERED TO YOU AT THE ADDRESS PROVIDED
ABOVE)

Dated:            __________________ , 2000

         This Subscription Agreement is agreed to and accepted as of ___________
, 2000.

                          ARONEX PHARMACEUTICALS, INC.

                          By:
                             ------------------------------------
                              Name: Geoffrey F. Cox, Ph.D.
                              Title:   President and Chief Executive Officer

                                       25
<PAGE>   26

CERTIFICATE OF SIGNATORY

(To be completed if Units are
being subscribed for by an entity)

                  I, ____________________________, am the _____________________
 of ___________________________ (the "Entity").

                  I certify that I am empowered and duly authorized by the
Entity to execute and carry out the terms of the Subscription Agreement and to
purchase and hold the Units, and certify further that the Subscription Agreement
has been duly and validly executed on behalf of the Entity and constitutes a
legal and binding obligation of the Entity.

                  IN WITNESS WHEREOF, I have set my hand this ________ day of
 _________________,______.

                                            -----------------------------------
                                            (Signature)

                                       26<PAGE>   1

                                                                    EXHIBIT 4.2

THE WARRANTS REPRESENTED BY THIS CERTIFICATE AND THE SECURITIES ISSUABLE UPON
EXERCISE THEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 OR
THE SECURITIES LAWS OF ANY STATE. NEITHER SUCH WARRANTS NOR SUCH SECURITIES MAY
BE SOLD, PLEDGED, HYPOTHECATED OR OTHERWISE TRANSFERRED WITHOUT SUCH
REGISTRATION, EXCEPT UPON DELIVERY TO THE COMPANY OF SUCH EVIDENCE AS MAY BE
SATISFACTORY TO COUNSEL FOR THE COMPANY TO THE EFFECT THAT ANY SUCH TRANSFER
SHALL NOT BE IN VIOLATION OF THE SECURITIES ACT OF 1933 OR APPLICABLE STATE
SECURITIES LAWS OR ANY RULE OR REGULATION PROMULGATED THEREUNDER.

                          ARONEX PHARMACEUTICALS, INC.

                          COMMON STOCK PURCHASE WARRANT

No. W-00- ___

         FOR VALUE RECEIVED, ARONEX PHARMACEUTICALS, INC., a Delaware
corporation (the "COMPANY"), hereby certifies that _______________ (the
"HOLDER"), its designee or its permitted assigns is entitled to purchase from
the Company, at any time or from time to time commencing on April 17, 2000 and
prior to 5:00 P.M., New York City time, on April 17, 2005 up to ______________
(_____) fully paid and non-assessable shares of common stock (subject to
adjustment), $.001 par value per share, of the Company for $3.00 per share (the
"PURCHASE AGREEMENT") (subject to adjustment as provided herein) and 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 for each of the Warrant Shares 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," and (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 50% of the outstanding Warrants and Warrant Shares are referred to
as the "MAJORITY OF THE HOLDERS"). The Aggregate Warrant Price is not subject to
adjustment.

<PAGE>   2

         By acceptance of this Warrant, the Holder agrees to comply with all
applicable provisions of the Purchase Agreement to the same extent as if it were
a party thereto.

         1. EXERCISE OF WARRANT. (a) This Warrant may be exercised in whole at
any time, or in part from time to time, commencing on April 17, 2000 and prior
to 5:00 P.M., Eastern Standard Time, on April 17, 2005 by the Holder by the
surrender of this Warrant (with the subscription form at the end hereof duly
executed) at the address set forth in Section 8(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

         (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.

         (c) 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 (i) 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 (ii) use its best
efforts to keep the Warrant Shares authorized for listing on the Nasdaq National
Market, the Nasdaq SmallCap Market or any national securities exchange on which
the Company's Common Stock is traded.

         3. PROTECTION AGAINST DILUTION. (a) If, at any time or from time to
time after the date of this Warrant, the Company shall issue or distribute to
any holder of shares of Common Stock evidence of its indebtedness, any other
securities of the Company or any cash, property or other assets (excluding a
subdivision, combination or reclassification, or dividend or distribution
payable in shares of Common Stock, referred to in Section 3(b), and also
excluding cash dividends or cash distributions paid

                                       2

<PAGE>   3

out of net profits legally available therefor in the full amount thereof (any
such non-excluded event being herein called a "SPECIAL DIVIDEND")), the Per
Share Warrant Price shall be adjusted by multiplying the Per Share Warrant Price
then in effect by a fraction, the numerator of which shall be the then Current
Market Price in effect on the record date of such issuance or distribution less
the fair market value (as determined in good faith by the Company's Board of
Directors) of the evidence of indebtedness, cash, securities or property, or
other assets issued or distributed in such Special Dividend applicable to one
share of Common Stock and the denominator of which shall be the then Current
Market Price in effect on the record date of such issuance or distribution. An
adjustment made pursuant to this Subsection 3(a) shall become effective
immediately after the record date of any such Special Dividend.

         (b) In case the Company shall hereafter (i) pay a dividend or make a
distribution to any holder of its capital stock in shares of Common Stock, (ii)
subdivide its outstanding shares of Common Stock into a greater number of
shares, (iii) combine its outstanding shares of Common Stock into a smaller
number of shares or (iv) issue by reclassification of its Common Stock any
shares of capital stock of the Company, 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 Holder
would have owned immediately following such action had such Warrant been
exercised immediately prior thereto. An adjustment made pursuant to this
Subsection 3(b) 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, combination or
reclassification.

         (c) No adjustment in the Per Share Warrant Price shall be required in
the case of the issuance by the Company of Common Stock (i) pursuant to the
exercise of any warrant; (ii) pursuant to the exercise of any stock options or
warrants currently outstanding or securities issued after the date hereof, which
may be approved by the Company's Board of Directors pursuant to any Company
benefit plan or exercised, under any employee benefit plan of the Company to
officers, directors, consultants or employees, but only with respect to such
warrants or stock options as are exercisable at prices no lower than the closing
bid price of the Common Stock as of the date of grant thereof.

         (d) 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

                                       3
<PAGE>   4

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(e) 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 thirty (30) 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.

         (e) No adjustment in the Per Share Warrant Price shall be required
unless such adjustment would require an increase or decrease of at least $0.05
per share of Common Stock; provided, however, that any adjustments which by
reason of this Subsection 3(g) are not required to be made shall be carried
forward and taken into account in any subsequent adjustment; provided, further,
however, that adjustments shall be required and made in accordance with the
provisions of this Section 3 (other than this Subsection 3(g)) not later than
such time as may be required in order to preserve the tax-free nature of a
distribution to the Holder of this Warrant or Common Stock issuable upon the
exercise hereof. All calculations under this Section 3 shall be made to the
nearest cent or to the nearest 1/100th of a share, as the case may be. Anything
in this Section 3 to the contrary notwithstanding, the Company shall be entitled
to make such reductions in the Per Share Warrant Price, in addition to those
required by this Section 3, as it in its discretion shall deem to be advisable
in order that any stock dividend, subdivision of shares or distribution of
rights to purchase stock or securities convertible or exchangeable for stock
hereafter made by the Company to its stockholders shall not be taxable.

         (f) 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 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.

         (g) If the Board of Directors of the Company shall declare any dividend
or other distribution with respect to the Common Stock other than a cash
distribution out of earned surplus, the Company shall mail notice thereof to the
Holders of the Warrants not less than ten (10) days prior to the record date
fixed for determining stockholders entitled to participate in such dividend or
other distribution.

         (h) If, as a result of an adjustment made pursuant to this Section 3,
the Holder of any Warrant thereafter surrendered for exercise shall become
entitled to

                                       4
<PAGE>   5

receive shares of two or more classes of capital stock or shares of Common Stock
and other capital stock of the Company, the Board of Directors (whose
determination shall be conclusive and shall be described in a written notice to
the Holder of any Warrant promptly after such adjustment) shall determine the
allocation of the adjusted Per Share Warrant Price between or among shares or
such classes of capital stock or shares of Common Stock and other capital stock.

         (i) Upon the expiration of any rights, options, warrants or conversion
privileges with respect to the issuance of which an adjustment to the Per Share
Warrant Price had been made, if such shall not have been exercised, the number
of Warrant Shares purchasable upon exercise of this Warrant, to the extent this
Warrant has not then been exercised, shall, upon such expiration, be readjusted
and shall thereafter be such as they would have been had they been originally
adjusted (or had the original adjustment not been required, as the case may be)
on the basis of (A) the fact that Common Stock, if any, actually issued or sold
upon the exercise of such rights, options, warrants or conversion privileges,
and (B) the fact that such shares of Common Stock, if any, were issued or sold
for the consideration actually received by the Company upon such exercise plus
the consideration, if any, actually received by the Company for the issuance,
sale or grant of all such rights, options, warrants or conversion privileges
whether or not exercised; provided, however, that no such readjustment shall
have the effect of decreasing the number of Warrant Shares purchasable upon
exercise of this Warrant by an amount in excess of the amount of the adjustment
initially made in respect of the issuance, sale or grant of such rights,
options, warrants or conversion privileges.

         (j) In case any event shall occur as to which the other provisions of
this Section 3 are not strictly applicable but as to which the failure to make
any adjustment would not fairly protect the purchase rights represented by this
Warrant in accordance with the essential intent and principles hereof then, in
each such case, the Board of Directors of the Company shall in good faith
determine the adjustment, if any, on a basis consistent with the essential
intent and principles established herein, necessary to preserve the purchase
rights represented by the Warrants. Upon such determination, the Company will
promptly mail a copy thereof to the Holder of this Warrant and shall make the
adjustments described therein.

         4. FULLY PAID STOCK; TAXES. The shares of the Common Stock represented
by each and every certificate for Warrant Shares delivered upon 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 all documentary, stamp or similar taxes and
other similar governmental charges that may be imposed with respect to the
issuance or delivery of any Common Shares upon exercise of the Warrants (other
than income taxes); provided, however, that if the Common Shares are to be
delivered in a name other than the name of the Holder, no such delivery shall be
made unless the person requesting the same has paid to the Company the amount of
transfer taxes or charges incident thereto, if any.

                                       5
<PAGE>   6

         5. REGISTRATION UNDER SECURITIES ACT OF 1933. (a) The Holder shall have
the right to participate in the registration rights granted to Holders of
Registrable Securities (as defined in the Subscription Agreement) with respect
to the Warrant Shares.

         (b) Until all of the Warrant Shares have been sold under a registration
statement declared effective by the Securities and Exchange Commission or
pursuant to Rule 144, the Company shall use its reasonable best efforts to file
with the Securities and Exchange Commission all current reports and the
information as may be necessary to enable the Holder to effect sales of its
shares in reliance upon Rule 144 promulgated under the Securities Act of 1933,
as amended (the "Act").

         6. 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 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 Act and any
applicable state securities laws or (ii) such sale or transfer is made pursuant
to one or more exemptions from the Act.

         (c) In addition to the limitations set forth in Section 1, this Warrant
may not be sold, transferred, assigned or hypothecated by the Holder except in
compliance with the provisions of the Act and the applicable state securities
"blue sky" laws, and is so transferable only upon the books of the Company which
it shall cause to be maintained for such purpose. The Company may treat the
registered Holder of this Warrant as he or 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 his 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.

                                       6
<PAGE>   7

         (d) The Holder has been afforded (i) the opportunity to ask such
questions as it has deemed necessary of, and to receive answers from,
representatives of the Company concerning the terms and conditions of the
Warrants or the exercise of the Warrants; and (ii) the opportunity to request
such additional information which the Company possesses or can acquire without
unreasonable effort or expense.

         (e) The Holder did not (i) receive or review any advertisement,
article, notice or other communication published in a newspaper or magazine or
similar media or broadcast over television or radio, whether closed circuit, or
generally available; or (ii) attend any seminar, meeting or investor or other
conference whose attendees were, to such Holder's knowledge, invited by any
general solicitation or general advertising.

         (f) The Holder is an "accredited investor" within the meaning of
Regulation D under the Act. Such Holder is acquiring the Warrants for its own
account and not with a present view to, or for sale in connection with, any
distribution thereof in violation of the registration requirements of the
Securities Exchange Act of 1934, without prejudice, however, to such Holder's
right, subject to the provisions of the Subscription Agreement and this Warrant,
at all times to sell or otherwise dispose of all or any part of such Warrants
and Warrant Shares.

         (g) Either by reason of such Holder's business or financial experience
or the business or financial experience of its professional advisors (who are
unaffiliated with and who are not compensated by the Company or any affiliate,
finder or selling agent of the Company, directly or indirectly), such Holder has
the capacity to protect such Holder's interests in connection with the
transactions contemplated by this Warrant and the Purchase Agreement.

         7. 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.

         8. 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.

         9. 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:

                                       7
<PAGE>   8

          (a) the Company at Aronex Pharmaceuticals, Inc., 8707 Technology
     Forest Place, The Woodlands, Texas 77381, Attn: Chief Financial Officer or
     such other address as the Company has designated in writing to the Holder,
     or

          (b) the Holder at __________________ or other such address as the
     Holder has designated in writing to the Company.

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

         11. APPLICABLE LAW. This Warrant shall be governed by and construed in
accordance with the laws of the State of Delaware without giving effect to the
principles of conflicts of law thereof.

         12. 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.

         IN WITNESS WHEREOF, the Company has caused this Warrant to be executed
this 17th day of April, 2000.

                                                ARONEX PHARMACEUTICALS, INC.

                                                By:
                                                   ---------------------------
                                                      Geoffrey F. Cox
                                                      Chief Executive Officer

                                       8
<PAGE>   9

                                  SUBSCRIPTION

                  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:
                                                        -----------------------

                                   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:
                                                        -----------------------

                               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 the Company.

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

                                       9

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