ARONEX PHARMACEUTICALS INC
POS AM, 1998-05-20
PHARMACEUTICAL PREPARATIONS
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      As filed with the Securities and Exchange Commission on May 20, 1998
                                                     Registration No. 33-91584

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


                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

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


                         POST-EFFECTIVE AMENDMENT NO. 2
                                       TO
                                    FORM S-3

             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

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

                          ARONEX PHARMACEUTICALS, INC.
             (Exact name of Registrant as specified in its charter)


               Delaware                                 76-0196535
    (State or other jurisdiction of      (I.R.S. Employer Identification Number)
     incorporation or organization)

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


                          8707 Technology Forest Place
                           The Woodlands, Texas 77381
                                 (281) 367-1666
  (Address, including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)

                               Terance A. Murnane
                                   Controller
                          8707 Technology Forest Place
                           The Woodlands, Texas 77381
                                 (281) 367-1666
 (Name, address, including zip code, and telephone number, including area code,
                              of agent for service)

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

                                   Copies to:
                             Andrews & Kurth L.L.P.
                        2170 Buckthorne Place, Suite 150
                           The Woodlands, Texas 77380
                              Jeffrey L. Wade, Esq.
                                 (713) 220-4801
                      ------------------------------------


         APPROPRIATE  DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC:  From
time to time after the effective date of this Registration Statement.

         If the only securities  being registered on this Form are being offered
pursuant  to a  dividend  or  interest  reinvestment  plans,  please  check  the
following box: /_/

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

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

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


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


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




<PAGE>

PROSPECTUS

                         [ARONEX PHARMACEUTICALS, INC.]


                               3,193,000 Shares of
                                  Common Stock
                       Issuable Upon Exercise of Warrants

         Aronex   Pharmaceuticals,   Inc.,  a  Delaware   corporation   ("Aronex
Pharmaceuticals"  or the  "Company")  is  offering up to  3,220,000  shares (the
"Shares")  of its Common  Stock,  par value $0.001 per share  ("Common  Stock"),
issuable  upon the  exercise of  outstanding  warrants to purchase  Common Stock
("Warrants"). The Common Stock is quoted on the Nasdaq National Market under the
trading  symbol  "ARNX".  On May 15, 1998,  the last  reported sale price of the
Common Stock on the Nasdaq National Market was $4-11/16 per share.

         Each Warrant entitles the holder thereof to purchase a specified number
of shares of Common Stock (as adjusted to give effect to a  one-for-two  reverse
split of the Common Stock that was effected on July 1, 1996) and is subject to a
Series A Exercise, Series B Exercise and a Series C Exercise. Subject to certain
exceptions, holders of Warrants were required to complete the Series A Exercise,
in whole but not in part,  prior to  December  28,  1995  (January 2, 1996 after
allowance  of a five day grace  period) to retain  any right to make  subsequent
exercises  under the  Warrant.  Holders of Warrants who  completed  the Series A
Exercise  prior to the  applicable  deadline have the right to make the Series B
Exercise  at any time prior to June 11,  1998,  in whole but not in part,  at an
effective  exercise  price of $8.00 per share.  Holders of Warrants who complete
the Series B Exercise prior to June 11, 1998 retain the right to make the Series
C Exercise at any time prior to December 11, 1999,  in whole but not in part, at
an  effective  exercise  price of $12.00 per share of Common  Stock.  Holders of
Warrants  who do not  complete  the  Series B  Exercise  prior to June 11,  1998
forfeit  any  right to make the  Series C  Exercise  under the  Warrant.  Aronex
Pharmaceuticals  has the right, at its option, to convert a Series B or Series C
Exercise into a "cashless" exercise based on the value of a Series B or Series C
Exercise  (equal to the fair market value per share of the Common Stock less the
exercise price per share) divided by the market price of the Common Stock at the
time of  exercise.  Prior to the purchase of Common Stock upon the exercise of a
Warrant, the holder of a Warrant will have none of the rights or privileges of a
stockholder of the Company.

         The number of Shares and the exercise prices of the Series B and Series
C Exercise give effect to a  one-for-two  reverse split of the Common Stock that
was effected on July 1, 1996.

         THE COMMON STOCK  OFFERED  HEREBY  INVOLVES A HIGH DEGREE OF RISK.  SEE
"RISK FACTORS" COMMENCING ON PAGE 5 OF THIS PROSPECTUS.

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


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



                  The date of this Prospectus is May 20, 1998.



<PAGE>



                              AVAILABLE INFORMATION

         The  Company  is  subject  to  the  informational  requirements  of the
Securities  Exchange  Act  of  1934,  as  amended  (the  "Exchange  Act"),  and,
accordingly,  files reports,  proxy  statements and other  information  with the
Securities and Exchange Commission (the "SEC").  Such reports,  proxy statements
and other  information  filed  with the SEC are  available  for  inspection  and
copying at the public reference  facilities  maintained by the SEC at Room 1024,
Judiciary Plaza, 450 Fifth Street, N.W., Washington,  DC 20549, and at the SEC's
Regional  Offices located at Citicorp  Center,  500 West Madison  Street,  Suite
1400, Chicago,  Illinois 60661 and at Seven World Trade Center,  Suite 1300, New
York,  New York 10048.  Copies of such  documents  may also be obtained from the
Public Reference Section of the SEC at Judiciary Plaza, 450 Fifth Street,  N.W.,
Washington, DC 20549, at prescribed rates. The SEC maintains a site on the World
Wide Web at http://www.sec.gov that contains reports, proxy statements and other
information  regarding  registrants  that file  electronically  with the SEC. In
addition,  such  materials and other  information  concerning the Company can be
inspected  at the National  Association  of  Securities  Dealers,  Inc.,  1735 K
Street, N.W., Washington, DC 20006.

         The  Company  has  filed  with the SEC a  registration  statement  (the
"Registration  Statement")  under the  Securities  Act of 1933,  as amended (the
"Securities   Act"),  on  Form  S-4  (Reg.  No.  33-91584),   as  amended  by  a
post-effective  amendment on Form S-3,  with respect to the  securities  offered
hereby. This Prospectus does not contain all of the information set forth in the
Registration  Statement  and the exhibits  thereto,  certain  parts of which are
omitted in accordance with the rules and regulations of the SEC. Statements made
in this  Prospectus  as to the  contents  of any  contract,  agreement  or other
document  referred to are not  necessarily  complete.  With respect to each such
contract,  agreement or other document  filed as an exhibit to the  Registration
Statement,  reference is made to the exhibit for a more complete  description of
the matter  involved.  The  Registration  Statement and any amendments  thereto,
including  exhibits filed or  incorporated  by reference as a part thereof,  are
available for inspection and copying at the SEC's offices as described above.

                       DOCUMENTS INCORPORATED BY REFERENCE

         The following documents,  which have been filed by the Company with the
SEC, are incorporated by reference into this Prospectus:

         1.       The Annual Report on Form 10-K for the fiscal year ended 
                  December 31, 1997;

         2.       The Quarterly Report on Form 10-Q for the quarterly period
                  ended March 31, 1998; and

         3.       The description of the Common Stock contained in the Company's
                  Registration  Statement  on Form 8-A  filed  April  23,  1992,
                  including any  amendments and reports filed for the purpose of
                  updating such description.

         All reports  and  documents  filed by the  Company  pursuant to Section
13(a),  13(c),  14 or 15(d)  of the  Exchange  Act,  prior  to the  filing  of a
post-effective amendment which indicates that all securities offered hereby have
been sold or which  deregisters all securities then remaining  unsold,  shall be
deemed to be incorporated  by reference  herein and to be a part hereof from the
respective date of filing of such documents.  Any statement  contained herein or
in a  document  all or a  portion  of  which is  incorporated  or  deemed  to be
incorporated  by reference  herein shall be deemed to be modified or  superseded
for purposes of this Prospectus to the extent that a statement  contained herein
or in any  other  subsequently  filed  document  that also is or is deemed to be
incorporated by reference herein modifies or supersedes such statement. Any such
statement so modified or superseded  shall not be deemed,  except as so modified
or superseded, to constitute a part of this Prospectus.

         THIS  PROSPECTUS  INCORPORATES  DOCUMENTS  BY  REFERENCE  WHICH ARE NOT
PRESENTED HEREIN OR DELIVERED HEREWITH. THE COMPANY HEREBY UNDERTAKES TO PROVIDE
WITHOUT CHARGE TO EACH PERSON, INCLUDING ANY BENEFICIAL OWNER, TO WHOM A COPY OF
THIS PROSPECTUS HAS BEEN  DELIVERED,  ON THE WRITTEN OR ORAL REQUEST OF ANY SUCH
PERSON, A COPY OF ANY AND ALL OF THE DOCUMENTS REFERRED TO ABOVE WHICH HAVE BEEN
OR MAY BE INCORPORATED IN THIS


                                       -2-

<PAGE>



PROSPECTUS BY  REFERENCE,  OTHER THAN  EXHIBITS TO SUCH  DOCUMENTS  (UNLESS SUCH
EXHIBITS ARE SPECIFICALLY  INCORPORATED BY REFERENCE INTO SUCH DOCUMENTS).  SUCH
REQUESTS FOR DOCUMENTS SHOULD BE DIRECTED TO ARONEX PHARMACEUTICALS,  INC., 8707
TECHNOLOGY  FOREST  PLACE,  THE  WOODLANDS,  TEXAS  77381,  ATTENTION:  INVESTOR
RELATIONS, TELEPHONE NUMBER (713) 367-1666.

         No  person  is  authorized  to give  any  information  or to  make  any
representation  not contained in this  Prospectus,  and, if given or made,  such
information or representation must not be relied upon as having been authorized.
This  Prospectus  does not constitute an offer to sell, or a solicitation  of an
offer to purchase,  any of the  securities  offered by this  Prospectus,  or the
solicitation of a proxy, in any jurisdiction in which, or to any person to whom,
it is  unlawful  to make  such  offer  or  solicitation  of an  offer  or  proxy
solicitation.  Neither the delivery of this  Prospectus nor any  distribution of
the  securities  offered  hereby  shall,  under any  circumstances,  create  any
implication  that the  information  contained  herein is  correct as of any time
subsequent to the date hereof or that there has been no change in the affairs of
the Company since the date hereof.





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





                                       -3-

<PAGE>



                                   THE COMPANY

         THE  FOLLOWING  IS  QUALIFIED  IN ITS  ENTIRETY  BY THE  MORE  DETAILED
INFORMATION  APPEARING  ELSEWHERE IN THIS  PROSPECTUS,  AND BY THE MORE DETAILED
INFORMATION AND FINANCIAL STATEMENTS,  INCLUDING NOTES THERETO,  INCLUDED IN THE
COMPANY'S ANNUAL REPORT ON FORM 10-K FOR THE YEAR ENDED DECEMBER 31, 1997 AND IN
SUBSEQUENT  REPORTS  FILED  PURSUANT TO SECTION 13 OR 15(D) OF THE EXCHANGE ACT,
WHICH ARE  INCORPORATED  BY REFERENCE  HEREIN.  THIS  PROSPECTUS AND THE REPORTS
INCORPORATED BY REFERENCE HEREIN CONTAIN "FORWARD-LOOKING STATEMENTS" WITHIN THE
MEANING  OF  SECTION  27A OF  THE  SECURITIES  ACT  OF  1933,  AS  AMENDED  (THE
"SECURITIES  ACT").  SUCH  STATEMENTS  REFLECT THE COMPANY'S  CURRENT VIEWS WITH
RESPECT TO FUTURE  EVENTS AND FINANCIAL  PERFORMANCE  AND ARE SUBJECT TO CERTAIN
RISKS,  UNCERTAINTIES  AND  ASSUMPTIONS  THAT COULD CAUSE ACTUAL RESULTS TO VARY
MATERIALLY FROM THOSE REFLECTED IN SUCH STATEMENTS, INCLUDING THOSE DISCUSSED IN
"RISK FACTORS" COMMENCING ON PAGE 5.

         Aronex   Pharmaceuticals,   Inc.  ("Aronex   Pharmaceuticals"   or  the
"Company")   is  an   emerging   biopharmaceutical   company   engaged   in  the
identification  and  development  of proprietary  innovative  medicines to treat
cancer and  infectious  diseases.  The  Company's  strategy is to  identify  and
develop  medicines  based upon either  refinements of proven  therapies or novel
mechanisms  of action  against  specific  disease  targets.  The  Company  has a
portfolio of clinical products that it believes provides a balanced  development
and commercialization  risk profile. The Company believes its focus on medicines
for cancer and infectious  diseases for which current therapy is inadequate will
provide  synergies in  development  and product  marketing  and will  facilitate
expedited commercialization of its products.

         Aronex Pharmaceuticals currently has four products in various stages of
ongoing  clinical  development.   In  addition,   the  Company  has  proprietary
technologies in drug formulation and drug delivery.  The Company's four products
in clinical development are (i) NYOTRAN(TM) for the treatment of systemic fungal
infections, (ii) ATRAGEN(R) for the treatment of cancer, (iii) Annamycin for the
treatment of cancers with  acquired  resistance  and (iv)  Zintevir(TM)  for the
treatment of human immunodeficiency virus ("HIV") infection.

         The Company has strategic alliances and collaboration arrangements with
leading  corporations  and  academic  institutions,   including  alliances  with
Boehringer   Mannheim  GmbH   ("Boehringer   Mannheim"),   Genzyme   Corporation
("Genzyme"), and Grupo Ferrer Internacional, S.A. ("Ferrer") and a collaboration
with The University of Texas M.D. Anderson Cancer Center ("MD Anderson").

         Aronex    Pharmaceuticals   was   incorporated   in   1986   as   Argus
Pharmaceuticals,  Inc. ("Argus"), and acquired Oncologix, Inc. ("Oncologix") and
Triplex Pharmaceutical  Corporation  ("Triplex") through a three-way merger (the
"Mergers")  in September  1995,  at which time Argus  changed its name to Aronex
Pharmaceuticals,   Inc.  The  merger  of  these  three  complementary  companies
established  an  integrated  company with the following  characteristics:  (i) a
clear therapeutic focus in cancer and infectious  diseases;  (ii) a well-defined
and diverse  portfolio  of products at various  stages of clinical  development;
(iii)  technologies in drug  formulation  and delivery;  (iv) a diverse group of
corporate  partners and academic  affiliations;  and (v) an experienced  team of
biopharmaceutical  personnel  who possess  the  ability to identify  and develop
novel products,  design and implement complex clinical trials, manage regulatory
issues,  develop manufacturing  processes and implement the commercialization of
products.  Unless the context otherwise  requires,  references in this report to
"Aronex  Pharmaceuticals" and the "Company" refer to Aronex  Pharmaceuticals and
its subsidiaries.

         The  Company's  corporate  headquarters  is located at 8707  Technology
Forest Place, The Woodlands, Texas 77381-1191, and its telephone number is (281)
367-1666.



                                       -4-

<PAGE>



                                  RISK FACTORS

         IN  EVALUATING  THE COMPANY  AND ITS  BUSINESS,  PROSPECTIVE  INVESTORS
SHOULD  CONSIDER  CAREFULLY  THE  FOLLOWING  RISK  FACTORS,  TOGETHER  WITH  THE
INFORMATION   AND  FINANCIAL  DATA  SET  FORTH  IN  THE  REPORTS  AND  DOCUMENTS
INCORPORATED BY REFERENCE HEREIN, PRIOR TO PURCHASING ANY SHARES OF COMMON STOCK
OFFERED HEREBY.

         Early Stage of Development;  History of Operating Losses;  Anticipation
of Future Losses.  The Company is a development stage company.  It has generated
no revenues from product sales,  and it does not expect to generate revenue from
product  sales for  several  years.  As of  December  31,  1997,  the  Company's
accumulated  deficit was $69.2 million.  To date, the Company has dedicated most
of its financial resources to the research and development of products,  general
and  administrative   expenses,  and  the  prosecution  of  patents  and  patent
applications.  The Company expects to incur significant and increasing operating
losses for at least the next several  years,  primarily  due to the expansion of
its  research  and  development  programs,  including  preclinical  studies  and
clinical trials, and costs associated with the commercialization of its products
if  regulatory  approvals  are  received.   The  Company's  ability  to  achieve
profitability  will  depend,  among other  things,  on  successfully  completing
development  of  its  products,  obtaining  regulatory  approvals,  establishing
manufacturing,  sales and marketing capabilities or collaborative  arrangements,
and  raising  sufficient  funds  to  finance  its  activities.  There  can be no
assurance  that  the  Company  will  be able to  achieve  profitability  or that
profitability, if achieved, can be sustained.

         Future Capital Needs;  Uncertainty of Additional  Funding.  The Company
has experienced  negative cash flows from operations since its inception and has
funded its activities to date primarily from equity financings.  The Company has
expended,  and will continue to require,  substantial funds to continue research
and  development,  including  preclinical  studies  and  clinical  trials of its
products,  and to commence  sales and  marketing  efforts if U.S.  Food and Drug
Administration  ("FDA") and other regulatory approvals are obtained. The Company
expects that its existing  capital  resources,  will be  sufficient  to fund its
capital  requirements  through  mid-1999.  Thereafter,  the Company will need to
raise  substantial  additional  capital to fund its  operations.  The  Company's
independent public accountants have informed the Company that if, at the time of
their audit of the financial  statements for the year ending  December 31, 1998,
the Company's  available capital resources are anticipated not to be adequate to
fund its operations  through  December 31, 1999, their report on those financial
statements will include an explanatory  paragraph  expressing  substantial doubt
about the  Company's  ability to continue  as a going  concern or, if there is a
material  uncertainty  whether  those  resources  will be  adequate  to fund its
operations for a reasonable period of time beyond December 31, 1999 will include
an  emphasis  of a matter  paragraph  concerning  the  Company's  need to obtain
additional  financing in order to complete  research and  development  and other
activities  necessary to  commercialize  its  products.  The  Company's  capital
requirements  will  depend on many  factors,  including  the  problems,  delays,
expenses  and   complications   frequently   encountered  by  development  stage
companies;  the progress of the  Company's  research,  development  and clinical
trial  programs;  the  Company's  ability to satisfy the extent and terms of any
future  collaborative  research,  manufacturing,   marketing  or  other  funding
arrangements;  the  costs and  timing of  seeking  regulatory  approvals  of the
Company's products;  the Company's ability to obtain regulatory  approvals;  the
success  of the  Company's  sales  and  marketing  programs;  costs  of  filing,
prosecuting and defending and enforcing any patent claims and other intellectual
property rights; and changes in economic,  regulatory or competitive  conditions
of the Company's planned  business.  Estimates about the adequacy of funding for
the  Company's  activities  are  based on  certain  assumptions,  including  the
assumption  that testing and  regulatory  procedures  relating to the  Company's
products can be conducted at  projected  costs.  There can be no assurance  that
changes in the Company's research and development plans, acquisitions,  or other
events will not result in accelerated or unexpected expenditures. To satisfy its
capital  requirements,  the  Company may seek to raise  additional  funds in the
public or private capital  markets.  The Company's  ability to raise  additional
funds in the public or private markets will be adversely affected if the results
of its current or future clinical trials are not favorable. The Company may seek
additional   funding  through  corporate   collaborations  and  other  financing
vehicles.  There can be no assurance  that any such funding will be available to
the Company on favorable  terms or at all. If adequate  funds are not available,
the Company may be required to curtail significantly one or more of its research
or  development  programs,  or it  may  be  required  to  obtain  funds  through
arrangements with future  collaborative  partners or others that may require the
Company to relinquish rights to some or all of its technologies or products.  If
the Company is successful in obtaining additional  financing,  the terms of such
financing may have the effect of diluting or adversely affecting the holdings or
the rights of the holders of the Company's Common Stock.



                                       -5-

<PAGE>



         Uncertainties  Related to  Clinical  Trial  Results.  The FDA and other
regulatory  authorities generally require that the safety and efficacy of a drug
be  supported by results from  adequate and  well-controlled  Phase III clinical
trials  before  approval for  commercial  sale.  If the results of the Company's
clinical  trials do not  demonstrate  the safety and efficacy of its products in
the  treatment of patients  suffering  from the diseases for which such products
are being tested,  the Company will not be able to submit a New Drug Application
(an "NDA") to the FDA. Clinical trials conducted on a fast-track,  or expedited,
basis may carry a higher  risk that data will not be  favorable  or that the FDA
will not  accept  the NDA for  submission  than do  Phase  III  clinical  trials
developed  from earlier  clinical  trials with large  populations  using similar
protocols.   Even  if  the  Company  believes  the  Phase  III  clinical  trials
demonstrate  the safety and  efficacy of a product in the  treatment of disease,
the FDA and other regulatory authorities may not accept the Company's assessment
of the  results.  In  either  case,  the  Company  may be  required  to  conduct
additional  clinical  trials in an effort to demonstrate the safety and efficacy
of the product.  Without acceptable results and regulatory approval, the Company
would not be able to  commercialize  its  products,  which would have a material
adverse effect on the Company. There can be no assurance that the results of any
of the  Company's  clinical  trials will be favorable or that its products  will
obtain regulatory approval for commercialization.

         The results of preclinical  studies and initial  clinical trials of the
Company's   products  are  not  necessarily   predictive  of  the  results  from
large-scale  clinical trials. The Company must demonstrate  through  preclinical
studies and clinical  trials that its products are safe and effective for use in
each target indication  before the Company can obtain  regulatory  approvals for
the  commercial  sale of those  products.  These  studies and trials may be very
costly and  time-consuming.  The speed with which the  Company is able to enroll
patients in clinical  trials is an important  factor in determining  how quickly
clinical  trials may be  completed.  Many  factors  affect  patient  enrollment,
including  the size of the  patient  population,  the  proximity  of patients to
clinical  sites,  and the  eligibility  criteria for the study.  A number of the
Company's  clinical trial protocols are targeted at indications  that have small
patient  populations,  which may make it  difficult  for the  Company  to enroll
enough  patients to complete  the trials.  Delays in patient  enrollment  in the
trials may result in increased costs,  program delays, or both, which could have
a material  adverse effect on the Company.  Even if the Company  establishes the
safety  and  efficacy  of its  products  and  obtains  FDA and other  regulatory
approvals for its products, physicians may not prescribe the approved product.

         The  administration  of any product the  Company  develops  may produce
undesirable  side  effects in  humans.  The  occurrence  of side  effects  could
interrupt or delay clinical trials of products and could result in the denial of
approval of the Company's  products for any or all targeted  indications  by the
FDA or other regulatory  authorities.  The Company,  the FDA or other regulatory
authorities  may suspend or terminate  clinical  trials at any time. Even if the
Company receives FDA and other regulatory approvals,  the Company's products may
later exhibit adverse effects that limit or prevent their widespread use or that
necessitate their withdrawal from the market. There can be no assurance that any
of the Company's products will be safe for human use.

         Government  Regulation;  No  Assurances  of  Regulatory  Approval.  The
Company's research and development activities,  preclinical studies and clinical
trials,  and  ultimately  the  manufacturing,  marketing  and  labeling  of  its
products,  are subject to extensive  regulation by the FDA and other  regulatory
authorities in the United States and other countries.  The United States Federal
Food, Drug and Cosmetic Act and the regulations promulgated thereunder and other
federal and state  statutes and  regulations  govern,  among other  things,  the
testing,  manufacture,  safety,  efficacy,  labeling,  storage,  record keeping,
approval, advertising and promotion of the Company's products. Preclinical study
and clinical trial  requirements and the regulatory  approval process take years
and require the  expenditure of  substantial  resources.  Additional  government
regulation may be established that could prevent or delay regulatory approval of
the Company's products.  Delays or rejections in obtaining  regulatory approvals
would adversely affect the Company's  ability to  commercialize  any product the
Company  develops  and the  Company's  ability to receive  product  revenues  or
royalties.  If  regulatory  approval of a product is granted,  the  approval may
include significant  limitations on the indicated uses for which the product may
be marketed.

         The FDA and other  regulatory  authorities  require that the safety and
efficacy  of the  Company's  therapeutic  products  must  be  supported  through
adequate and well-controlled  Phase III clinical trials. If the results of Phase
III clinical  trials do not  establish  the safety and efficacy of the Company's
products to the satisfaction of the FDA and other


                                       -6-

<PAGE>



regulatory authorities,  the Company will not receive the approvals necessary to
market its products, which would have a material adverse effect on the Company.

         The standard process required by the FDA before a pharmaceutical  agent
may be marketed in the United  States  includes:  (i)  preclinical  tests;  (ii)
submission  to the  FDA of an IND  which  must  become  effective  before  human
clinical trials may commence;  (iii) adequate and well-controlled human clinical
trials  to  establish  the  safety  and  efficacy  of the  drug in its  intended
application;  (iv)  submission of an NDA to the FDA; and (v) FDA approval of the
NDA prior to any  commercial  sale or  shipment  of the  drug.  In  addition  to
obtaining FDA approval for each product,  each drug manufacturing  establishment
must be inspected and approved by the FDA. All manufacturing  establishments are
subject to inspections by the FDA and by other federal, state and local agencies
and must comply with current GMP requirements.

         Preclinical tests include  laboratory  evaluation of product chemistry,
formulation  and  stability,  as well as animal  studies to assess the potential
safety and efficacy of each product.  Preclinical safety tests must be conducted
by  laboratories  that comply with FDA  regulations  regarding  Good  Laboratory
Practices. The results of the preclinical tests are submitted to the FDA as part
of an IND and are reviewed by the FDA before the  commencement of human clinical
trials.  Unless the FDA objects to an IND, the IND will become effective 30 days
following its receipt by the FDA. There can be no assurance  that  submission of
an IND will result in the FDA  authorization to commence clinical trials or that
the lack of an objection means that the FDA will ultimately approve an NDA.

         Clinical trials involve the administration of the  investigational  new
drug to humans  under the  supervision  of a qualified  principal  investigator.
Clinical  trials must be conducted in accordance  with Good  Clinical  Practices
under  protocols that detail the  objectives of the study,  the parameters to be
used to monitor  safety,  and efficacy  criteria to be evaluated.  Each protocol
must be submitted to the FDA as part of the IND. Also,  each clinical trial must
be approved and conducted  under the auspices of an  Institutional  Review Board
("IRB"). The IRB will consider,  among other things, ethical factors, the safety
of human subjects,  and the possible liability of the institution conducting the
clinical trials.

         Clinical  trials are  typically  conducted in three  sequential  phases
which may overlap.  In Phase I, the initial  introduction of the drug to humans,
the drug is tested for safety (adverse effects),  dosage tolerance,  metabolism,
distribution,  excretion and pharmacodynamics (clinical pharmacology).  Phase II
involves  studies of a limited  patient  population to gather evidence about the
efficacy of the drug for specific  targeted  indications,  dosage  tolerance and
optimal dosage,  and to identify possible adverse effects and safety risks. When
a product has shown evidence of efficacy and has an acceptable safety profile in
a Phase II  evaluation,  Phase III clinical  trials are  undertaken  to evaluate
clinical  efficacy and to test for safety in an expanded  patient  population at
geographically  dispersed  clinical trial sites.  There can be no assurance that
any of the Company's  clinical  trials will be completed  successfully or within
any specified time period. The Company or the FDA may suspend clinical trials at
any time.

         The Company has designed the protocols for its pivotal  clinical trials
based on its analysis of its  research,  including  various parts of its Phase I
and Phase II clinical  trials.  Although  copies of its pivotal  clinical  trial
protocols  have been  submitted to the FDA,  there can be no assurance  that the
FDA, after the results of the pivotal clinical trials have been announced,  will
not  disagree  with the  design of the  pivotal  clinical  trial  protocols.  In
addition,  the FDA inspects and reviews  clinical trial sites,  informed consent
forms,  data from the  clinical  trial  sites,  including  case report forms and
record  keeping  procedures,  and the  performance  of the protocols by clinical
trial personnel to determine  compliance with Good Clinical  Practices.  The FDA
also  looks to  determine  that  there was no bias in the  conduct  of  clinical
trials.  The conduct of clinical  trials in general and the  performance  of the
pivotal  clinical  trial  protocols  is complex and  difficult.  There can be no
assurance  that the design or the  performance  of the  pivotal  clinical  trial
protocols will be successful.

         The results of preclinical  studies and clinical trials, if successful,
are  submitted  in an NDA to seek FDA approval to market and  commercialize  the
drug product for a specified use. The testing and approval  process will require
substantial  time and effort,  and there can be no  assurance  that any approval
will be granted for any product or that  approval  will be granted  according to
any schedule.  The FDA may deny an NDA if it believes that applicable regulatory
criteria  are not  satisfied.  The FDA may also require  additional  testing for
safety and efficacy of the drug.


                                       -7-

<PAGE>



Moreover, if regulatory approval of a drug product is granted, the approval will
be limited to specific  indications.  There can be no assurance  that any of the
Company's   product   candidates   will   receive   regulatory   approvals   for
commercialization.

         Even if regulatory  approvals for the Company's  products are obtained,
the Company,  its  products,  and the  facilities  manufacturing  the  Company's
products are subject to continual review and periodic  inspection.  The FDA will
require  post-marketing  reporting  to  monitor  the  safety  of  the  Company's
products.  Each drug manufacturing  establishment must be inspected and approved
by the FDA. All manufacturing establishments are subject to biennial inspections
by the FDA and must comply with the FDA's Good  Manufacturing  Practices ("GMP")
requirements.  To supply drug  products  for use in the United  States,  foreign
manufacturing establishments must comply with the FDA's GMP requirements and are
subject to periodic inspection by the FDA or by regulatory  authorities in those
countries  under  reciprocal  agreements  with the FDA.  In  complying  with GMP
requirements,  manufacturers  must expend funds,  time and effort in the area of
production and quality control to ensure full technical compliance.  The Company
does not have any drug  manufacturing  capability and must rely on outside firms
for this  capability.  The FDA  stringently  applies  regulatory  standards  for
manufacturing.  Identification of previously  unknown problems with respect to a
product,  manufacturer  or facility may result in  restrictions  on the product,
manufacturer or facility,  including warning letters,  suspensions of regulatory
approvals,  operating  restrictions,  delays in obtaining new product approvals,
withdrawal of the product from the market, product recalls,  fines,  injunctions
and criminal prosecution.

         Before the  Company's  products  can be marketed  outside of the United
States,  they are subject to regulatory  approval similar to FDA requirements in
the United States,  although the requirements  governing the conduct of clinical
trials,  product licensing,  pricing, and reimbursement vary widely from country
to country. No action can be taken to market any drug product in a country until
an appropriate  application  has been approved by the regulatory  authorities in
that  country.  FDA  approval  does not  assure  approval  by  other  regulatory
authorities.  The current approval  process varies from country to country,  and
the time spent in gaining  approval  varies from that required for FDA approval.
In some countries,  the sale price of a drug product must also be approved.  The
pricing review period often begins after market  approval is granted.  Even if a
foreign  regulatory  authority  approves  any  of  the  Company's  products,  no
assurance  can be  given  that  it  will  approve  satisfactory  prices  for the
products.

         The Company's  research and development  involves the controlled use of
hazardous  materials,  chemicals,  viruses,  and various radioactive  compounds.
Although the Company  believes that its procedures for handling and disposing of
those  materials  comply  with  state  and  federal  regulations,  the  risk  of
accidental contamination or injury from these materials cannot be eliminated. If
such an accident occurs, the Company could be held liable for resulting damages,
which could be material to the Company's financial  condition and business.  The
Company is also subject to numerous  environmental,  health and workplace safety
laws and regulations,  including those governing laboratory procedures, exposure
to blood-borne pathogens, and the handling of biohazardous materials. Additional
federal,  state and local laws and  regulations  affecting  the  Company  may be
adopted in the future.  Any violation of, and the cost of compliance with, these
laws and regulations could materially and adversely affect the Company.

         Uncertainty of Protection for Patents and Proprietary  Technology.  The
Company's  ability to commercialize  any products will depend, in part, upon its
or its licensors'  ability to obtain  patents,  enforce those patents,  preserve
trade secrets,  and operate without  infringing  upon the proprietary  rights of
third  parties.   The  patent  positions  of  biotechnology  and  pharmaceutical
companies are highly uncertain and involve complex legal and factual  questions.
Some of the United States patents and patent  applications  owned by or licensed
to the Company are method-of-use patents that cover the use of certain compounds
to  treat  specified  conditions,  and  composition-of-matter  patents  are  not
available for some of the  Company's  product  candidates.  The Company does not
have any patents or patent  applications for one of its products,  AR102.  There
can be no  assurance  that the patent  applications  licensed to or owned by the
Company will result in issued  patents,  that patent  protection will be secured
for any particular technology,  that any patents that have been or may be issued
to the Company or its licensors will be valid or  enforceable,  that any patents
will provide meaningful  protection to the Company, that others will not be able
to design  around the  patents,  or that the  Company's  patents  will provide a
competitive advantage or have commercial application.



                                       -8-

<PAGE>



         There can be no  assurance  that  patents  owned by or  licensed to the
Company will not be  challenged by others.  The Company could incur  substantial
costs in  proceedings  before the United States Patent and Trademark  Office and
other  regulatory  authorities,   including  interference   proceedings.   These
proceedings  could result in adverse  decisions about the  patentability  of the
Company's inventions and products as well as about the enforceability,  validity
or scope of  protection  afforded  by the  patents.  The  Company  is  currently
involved  in an  interference  proceeding  before the United  States  Patent and
Trademark Office regarding AR726.

         There  can be no  assurance  that the  manufacture,  use or sale of the
Company's  product  candidates  will not infringe  patent rights of others.  The
Company may be unable to avoid infringement of those patents and may be required
to seek a license,  defend an infringement  action, or challenge the validity of
the patents in court. There can be no assurance that a license will be available
to the Company,  if at all, upon terms and conditions  acceptable to the Company
or that the Company will prevail in any patent litigation.  Patent litigation is
costly and time  consuming,  and there can be no assurance that the Company will
have sufficient  resources to bring such litigation to a successful  conclusion.
If the Company does not obtain a license under such patents, is found liable for
infringement,  or is not able to have such patents declared invalid, the Company
may be liable for significant money damages, may encounter significant delays in
bringing  products to market,  or may be  precluded  from  participating  in the
manufacture,  use or sale of products  or methods of  treatment  requiring  such
licenses.  The  Company  does  not  believe  that the  commercialization  of its
products will infringe upon the patent rights of others.  However,  there can be
no assurance that the Company has identified  United States and foreign  patents
that pose a risk of infringement.

         The  Company  also  relies  upon  trade  secrets  and other  unpatented
proprietary information in its product development activities. To the extent the
Company  relies  on trade  secrets  and  unpatented  know-how  to  maintain  its
competitive  technological  position,  there can be no assurance that others may
not independently develop the same or similar technologies. The Company seeks to
protect trade secrets and proprietary knowledge, in part through confidentiality
agreements  with  its  employees,   consultants,   advisors  and  collaborators.
Nevertheless,  these  agreements may not effectively  prevent  disclosure of the
Company's  confidential  information  and may not provide  the  Company  with an
adequate remedy in the event of unauthorized disclosure of such information.  If
the  Company's  employees,   scientific  consultants  or  collaborators  develop
inventions  or processes  independently  that may be applicable to the Company's
products,  disputes  may arise about  ownership of  proprietary  rights to those
inventions and  processes.  Such  inventions and processes will not  necessarily
become the Company's  property,  but may remain the property of those persons or
their employers.  Protracted and costly litigation could be necessary to enforce
and determine the scope of the Company's  proprietary rights.  Failure to obtain
or maintain  patent and trade secret  protection,  for any reason,  would have a
material adverse effect on the Company.

         The Company engages in collaborations,  sponsored research  agreements,
licensing and other arrangements with academic researchers and institutions that
have received and may receive funding from United States government agencies. As
a result of these  arrangements,  the United States  government or certain third
parties  have rights in certain  inventions  developed  during the course of the
performance  of such  collaborations  and  agreements as required by law or such
agreements.

         Several  bills  affecting  patent  rights have been  introduced  in the
United  States  Congress.  These bills  address  various  aspects of patent law,
including  publication,   patent  term,   re-examination,   subject  matter  and
enforceability.  It is not  certain  whether  any of these bills will be enacted
into law or what form new laws may take. Accordingly,  the effect of legislative
change on the Company's intellectual property estate is uncertain.

         Manufacturing  Uncertainties;  Reliance on Third-Party  Suppliers.  The
Company  does not have the staff or  facilities  necessary  to  manufacture  its
products,  but it does have the capability to develop  formulations,  analytical
methods,  process controls and  manufacturing  technology for its products.  The
Company uses contract manufacturers to produce larger quantities of its products
for clinical testing.  Production is done on a per-purchase-order basis, and the
Company  and its  contract  manufacturers  have not  entered  into  any  written
agreements.   The  Company  does  not  expect  to  establish   any   significant
manufacturing capacity in the near future. The Company does not operate and does
not currently plan to operate manufacturing facilities for the production of its
products in commercial quantities, and it intends to contract with third parties
for the manufacture and supply of its products. There can be no assurance that


                                       -9-

<PAGE>



the Company  will be able to obtain  supplies of its products  from  third-party
suppliers  on  terms or in  quantities  acceptable  to the  Company.  Also,  the
Company's  dependence on third parties for the  manufacture  of its products may
adversely  affect the Company's  product  margins and its ability to develop and
deliver  products  on a timely  basis.  Any such  third-party  suppliers  or any
manufacturing  facility the Company establishes will be required to meet FDA GMP
requirements. FDA inspection and approval of manufacturing facilities for a drug
are a  prerequisite  to  approval  of an NDA for  that  drug.  The  Company  may
encounter   significant   delays  in   obtaining   supplies   from   third-party
manufacturers  or experience  interruptions  in its supplies.  If the Company is
unable to obtain adequate supplies,  its business would be materially  adversely
affected.

         The raw materials  required for the majority of the Company's  products
are  currently  available  in  quantities  sufficient  to conduct the  Company's
research,  development,  preclinical safety and clinical development activities.
Certain of the Company's  products,  such as Annamycin,  are new syntheses  and,
therefore,  are not yet available in commercial quantities.  No assurance can be
given that the raw  materials  necessary  for the  manufacture  of the Company's
products  will be available in sufficient  quantities  or at a reasonable  cost.
Complications  or delays in obtaining raw materials or in product  manufacturing
could  delay  the  submission  of  products  for  regulatory  approval  and  the
initiation  of new  development  programs,  which  could  materially  impair the
Company's competitive position and potential profitability.

         Lack of Sales and Marketing  Experience.  The Company does not have any
experience in sales,  marketing or distribution.  To market any of its products,
the  Company  must  develop  a  sales  and  marketing   force  with   supporting
distribution  capability or enter into marketing and  distribution  arrangements
with a  company  that  has an  established  capability.  Significant  additional
expenditures will be required for the Company to develop such capabilities.  The
Company has entered into an agreement with Genzyme with respect to marketing and
selling  ATRAGEN,  and it plans to enter into marketing  agreements  with one or
more  other  pharmaceutical  companies  to  market  other  products  that it may
develop.  To  the  extent  the  Company  relies  upon  licensing,  marketing  or
distribution  arrangements  with others,  any revenues the Company receives will
depend upon the efforts of third  parties.  There can be no  assurance  that any
third  party  will  market  the  Company's  products  successfully  or that  any
third-party  collaboration  will be on terms  favorable to the  Company.  If any
marketing partner does not market a product successfully, the Company's business
would be  materially  adversely  affected.  There can be no  assurance  that the
Company will be able to establish sales, marketing and distribution capabilities
or that it or its collaborators  will be successful in gaining market acceptance
for any  products  that the  Company  may  develop.  The  Company's  failure  to
establish  marketing  capabilities or to enter into marketing  arrangements with
third parties would have a material adverse effect on the Company.

         Risks Associated with Collaborative Arrangements. The Company's product
development and  commercialization  strategy  involves the Company entering into
various  arrangements  with  corporate,  government and academic  collaborators,
licensors,  licensees and others.  As a consequence,  the Company's  success may
depend  on  the   success   of  these   other   parties  in   performing   their
responsibilities.  There can be no  assurance  that the Company  will be able to
establish additional  collaborative  arrangements or license agreements that are
necessary or desirable for the Company to develop and commercialize its products
or  that  any  such  collaborative   agreement  or  license  agreement  will  be
successful.   Some  of  the  Company's  collaborative   agreements  and  license
agreements provide for milestone payments to the Company, and others require the
Company to pay milestone  payments to others. No assurance can be given that the
Company will achieve the milestones  that trigger  payments to the Company,  nor
can  assurance  be  given  that  payments  by the  Company  will  result  in the
development of marketable  products.  No assurance can be given that any current
or future  collaborative  arrangement  will be renewed at the end of its term or
will be renewed on terms as favorable to the Company as its original terms.



                                      -10-

<PAGE>



         Competition and  Technological  Change.  The Company  believes that its
products, because of their unique pharmacologic profiles and novel mechanisms of
action,  will become  useful new  treatments  for  cancers and  life-threatening
infectious  diseases,  either as  alternatives  to or in combination  with other
pharmaceuticals.  The Company is engaged in pharmaceutical  product  development
characterized by rapid technological  progress.  Many established  biotechnology
and pharmaceutical companies,  universities and other research institutions with
resources  significantly  greater than those of the Company may develop products
that directly compete with the Company's products. Those entities may succeed in
developing products, including liposomes and liposomal products, that are safer,
more effective or less costly than the Company's products. Even if the Company's
products  should  prove  to be more  effective  than  those  developed  by other
companies,  other  companies may be more  successful than the Company because of
greater financial  resources,  greater experience in conducting  preclinical and
clinical trials and obtaining regulatory approval,  stronger sales and marketing
efforts,  earlier receipt of approval for competing  products and other factors.
If the Company commences significant commercial sales of its products, it or its
collaborators  will  compete  in areas in which  the  Company  has  little or no
experience such as manufacturing  and marketing.  There can be no assurance that
the Company's  products,  if commercialized,  will be accepted and prescribed by
healthcare professionals.

         Some of the  Company's  competitors  are active in the  development  of
liposome  and  liposomal  research and product  development  to treat cancer and
certain fungal  infections.  Those competitors  include SEQUUS  Pharmaceuticals,
Inc.,  NeXstar  Pharmaceuticals,  Inc., and The Liposome  Company,  Inc. Some of
those  companies'  products  have  regulatory  approval in the United States and
other  countries.  Any marketing of these and other  products that treat disease
indications targeted by the Company could adversely affect the market acceptance
of the Company's  products as a result of the established market recognition and
physician  familiarity  with the  competing  product.  The  presence of directly
competitive  products could also result in more intense price  competition  than
might  otherwise  exist,  which  could  have a  material  adverse  effect on the
Company's  financial  condition and results of operations.  The Company believes
that competition will be intense for all of its product candidates.

         No  Assurance  of Adequate  Third-Party  Reimbursement.  The  Company's
ability to commercialize  its products  successfully  will depend in part on the
extent to which  appropriate  reimbursement  levels for the cost of the products
and related treatment are obtained from government  authorities,  private health
insurers  and  other  organizations,  such as health  maintenance  organizations
("HMOs"). Third-party payors are increasingly challenging the prices charged for
medical products and services.  Accordingly, if less costly drugs are available,
third-party  payors may not authorize  reimbursement for the Company's  products
even if they offer  advantages  in safety or  efficacy.  Also,  the trend toward
managed  healthcare  and  government   insurance  programs  could  significantly
influence the purchase of healthcare  services and products,  resulting in lower
prices and reducing  demand for the  Company's  products.  The cost  containment
measures that healthcare  providers are  instituting  and any healthcare  reform
could affect the Company's  ability to sell its products and may have a material
adverse effect on the Company.

         There can be no assurance  that  reimbursement  in the United States or
foreign countries will be available for any of the Company's products,  that any
reimbursement  granted  will be  maintained,  or that  limits  on  reimbursement
available from third-party  payors will not reduce the demand for, or negatively
affect the price of, the Company's products. The unavailability or inadequacy of
third-party  reimbursement  for the  Company's  products  would  have a material
adverse effect on the Company. The Company is unable to forecast what additional
legislation  or regulation  relating to the  healthcare  industry or third-party
coverage  and  reimbursement  may be enacted in the  future,  or what effect the
legislation or regulation would have on the Company's business.

         Potential  Product  Liability;  Availability of Insurance.  The Company
risks exposure to product liability claims if the use of its products is alleged
to have an adverse effect on subjects or patients. This risk exists for products
tested in human clinical trials as well as products that are sold  commercially.
There can be no assurance  that product  liability  claims,  if made,  would not
result in a recall of the Company's  products or a change in the indications for
which  they may be used.  The  Company  maintains  product  liability  insurance
coverage for claims  arising  from the use of its  products in clinical  trials.
There can be no assurance  that this  coverage will be adequate to cover claims.
Product liability insurance is becoming increasingly expensive, and no assurance
can be given that the Company will be able to maintain  such  insurance,  obtain
additional insurance,  or obtain insurance at a reasonable cost or in sufficient
amounts to protect the Company against losses that could have a material adverse
effect on the Company.


                                      -11-

<PAGE>



         Control by Existing  Stockholders.  As of April 30, 1998, the Company's
directors and executive  officers and their respective  affiliates  beneficially
owned   approximately   14.2%  of  the  Company's   outstanding   Common  Stock.
Accordingly,  such persons may be able to determine the composition of the board
of  directors  and may be able to  influence  the  outcome of other  stockholder
votes, including votes concerning the adoption or amendment of provisions in the
Company's Amended and Restated Certificate of Incorporation (the "Certificate of
Incorporation")  and the  approval  of mergers and other  significant  corporate
transactions.  The existence of these levels of ownership  concentrated in a few
persons  makes it unlikely that any other holder of Common Stock will be able to
affect the management or direction of the Company. These factors, along with the
factors described in "-- Anti-Takeover  Provisions," may also have the effect of
delaying  or  preventing  a change in the  management  or voting  control of the
Company.

         Dependence  on Key  Personnel.  The success of the  Company  depends in
large  part on the  Company's  ability to attract  and retain  highly  qualified
scientific  and management  personnel.  The Company faces  competition  for such
personnel from other companies,  research and academic institutions,  government
entities and other  organizations.  There can be no  assurance  that the Company
will be successful in hiring or retaining key personnel.

         Shares  Eligible  for  Future  Sale;  Registration  Rights.  Sales of a
substantial number of shares of Common Stock in the public market following this
offering could  adversely  affect the market price for the Common Stock.  Of the
15,467,281 shares of Common Stock  outstanding as of April 30, 1998,  14,041,150
shares are eligible for sale without  restriction  under the  Securities  Act of
1933, as amended (the "Securities Act") (except for shares held by affiliates of
the  Company  whose  shares may be sold  subject to the volume  limitations  and
certain other  requirements of Rule 144 under the Securities Act), and 1,426,131
shares are  restricted  securities  that may not be resold unless such resale is
registered  under the  Securities  Act or it is made  under  Rule 144 or another
exemption from registration under the Securities Act. Any such sales may have an
adverse  effect on the price of the Company's  Common Stock and could impair the
Company's ability to raise capital through offerings of equity  securities.  See
"Description of the Company's Securities -- Registration Rights."

         Immediate and Substantial Dilution; Contingent Stock Rights; Absence of
Dividends.  Purchasers  of the Common Stock in the offering  will  experience an
immediate and substantial  dilution in net tangible book value per share.  These
investors  will  also  experience  additional  dilution  upon  the  exercise  of
outstanding  options and  warrants.  In  addition,  pursuant to the terms of the
mergers in which the Company acquired Triplex, the Company is obligated to issue
shares of Common Stock to certain former  securityholders  of Triplex contingent
upon the occurrence of certain  events.  These rights may result in the issuance
of up to an aggregate of $5.0 million of Common  Stock,  valued for such purpose
at the current market value of the Common Stock at the time the event  requiring
issuance of such shares occurs. See "Dilution" and "Description of the Company's
Securities -- Contingent  Stock Rights." The Company does not anticipate  paying
cash dividends in the foreseeable future.

         Limited  Trading  Volumes;   Possible  Stock  Price   Volatility.   The
historical trading volume of the Company's Common Stock has been limited.  There
can be no  assurance  that an active  public  market for the  Common  Stock will
develop or be sustained.  The trading price of the Common Stock and the price at
which the Company may sell  securities  in the future  could be subject to large
fluctuations in response to announcements of research activities,  technological
innovations  or new  products  by the  Company  or its  competitors,  changes in
government regulations,  developments  concerning proprietary rights,  quarterly
variations  in  operating  results,  litigation,  clinical  trials of  products,
approval or denial of NDAs,  general  market  conditions,  the  liquidity of the
Company and its ability to raise additional  funds and other events.  The market
price of the Common  Stock,  and the market  prices for  securities  of emerging
biotechnology  companies  generally,  have experienced  extreme  fluctuations in
recent years.  These fluctuations have sometimes been unrelated to the operating
performance  of the affected  companies.  These market  fluctuations  as well as
general  fluctuations  in the stock  markets  may also  affect  the price of the
Common Stock.

         Anti-Takeover  Provisions.  The Company's  Certificate of Incorporation
(i) provides for staggered terms of office for directors;  (ii) requires certain
procedures  to be followed  and time  periods to be met for any  stockholder  to
propose matters to be considered at annual meetings of  stockholders,  including
nominating   directors  for  election  at  those   meetings;   (iii)   prohibits
stockholders from calling special meetings of stockholders;  and (iv) authorizes
the Board of


                                      -12-

<PAGE>



Directors  of the Company to issue up to  5,000,000  shares of  preferred  stock
without  stockholder  approval  and to set the  rights,  preferences  and  other
designations, including voting rights, of those shares as the Board of Directors
may determine.  These  provisions,  alone or in combination  with each other and
with the  matters  described  in "--  Control  by  Existing  Stockholders,"  may
discourage  transactions involving actual or potential changes of control of the
Company,  including  transactions  that  otherwise  could  involve  payment of a
premium over  prevailing  market prices to holders of Common Stock.  The Company
also is subject to provisions of the Delaware  General  Corporation Law that may
make  some  business  combinations  more  difficult.  See  "Description  of  the
Company's  Securities -- Certain  Provisions of the Company's Charter and Bylaws
and Delaware Law."

         Forward-Looking   Statements  and  Associated  Risks.  This  Prospectus
contains   forward-looking   statements.   The  words  "anticipate,"  "believe,"
"expect," "estimate," "project" and similar expressions are intended to identify
forward-looking  statements. Such statements reflect the Company's current views
with  respect to future  events and  financial  performance  and are  subject to
certain risks,  uncertainties  and  assumptions,  including the risk factors set
forth above. Should one or more of these risks or uncertainties materialize,  or
should  underlying   assumptions  prove  incorrect,   actual  results  may  vary
materially from those anticipated, believed, expected, estimated or projected.



                                      -13-

<PAGE>



                     DESCRIPTION OF THE COMPANY'S SECURITIES

GENERAL

         The Company's  Certificate  of  Incorporation  provides for  authorized
capital stock of 35,000,000  shares,  consisting of 30,000,000  shares of common
stock,  par value $0.001 per share, and 5,000,000 shares of preferred stock, par
value $0.001 per share. The following  summary  description of the capital stock
of the Company is qualified in its entirety by reference to the  Certificate  of
Incorporation,  a copy of  which  is filed  as an  exhibit  to the  Registration
Statement of which this Prospectus is a part.

COMMON STOCK

         Holders  of  Common  Stock  are  entitled  to one vote per share in the
election  of  directors  and on all  other  matters  on which  stockholders  are
entitled  or  permitted  to vote.  Holders of Common  Stock are not  entitled to
cumulative voting rights. Therefore,  holders of a majority of the shares voting
for the election of directors can elect all the directors.  Subject to the terms
of any outstanding  series of Preferred  Stock,  the holders of Common Stock are
entitled to  dividends  in such  amounts and at such times as may be declared by
the Company's Board of Directors out of funds legally  available  therefor.  See
"Dividend Policy." Upon liquidation or dissolution,  holders of Common Stock are
entitled  to share  ratably  in all net assets  available  for  distribution  to
stockholders  after  payment  of  any  liquidation  preferences  to  holders  of
Preferred  Stock.  Holders of Common  Stock have no  redemption,  conversion  or
preemptive rights.

PREFERRED STOCK

         The Board of Directors  has the authority to cause the Company to issue
up to the authorized  number of shares of Preferred Stock in one or more series,
to  designate  the  number of shares  constituting  any  series,  and to fix the
rights,  preferences,  privileges and restrictions  thereof,  including dividend
rights,  voting  rights,   redemption  and  conversion  rights  and  liquidation
preferences  of such series,  without  further action by the  stockholders.  The
issuance of  Preferred  Stock with voting and  conversion  rights may  adversely
affect the voting power of the holders of the Common Stock.
The Company has no present plan to issue any shares of Preferred Stock.

WARRANTS

         As of May 15,  1998,  the Company had  outstanding  warrants  issued in
connection with financing transactions to purchase an aggregate of 60,623 shares
of Common Stock.  In addition,  as of May 15, 1998, the Company had  outstanding
Warrants  issued in connection  with the September 1995 merger with Oncologix to
purchase an aggregate of  approximately  3,193,000  shares of Common Stock.  The
Warrants are not transferable except under certain limited  circumstances.  Each
Warrant  entitles the holder thereof to purchase a specified number of shares of
Common Stock (as adjusted to give effect to a  one-for-two  reverse split of the
Common  Stock  that was  effected  on July 1, 1996) and is subject to a Series A
Exercise,  Series B  Exercise  and a  Series  C  Exercise.  Subject  to  certain
exceptions, holders of Warrants were required to complete the Series A Exercise,
in whole but not in part,  prior to  December  28,  1995  (January 2, 1996 after
allowance  of a five day grace  period) to retain  any right to make  subsequent
exercises under the Warrant.

         Holders of Warrants who  completed  the Series A Exercise  prior to the
applicable  deadline  have the right to make the Series B  Exercise  at any time
prior to June 11, 1998, in whole but not in part, at an effective exercise price
of $8.00 per share. Holders of Warrants who complete the Series B Exercise prior
to June 11,  1998  retain the right to make the  Series C  Exercise  at any time
prior to December 11, 1999, in whole but not in part,  at an effective  exercise
price of $12.00  per share of  Common  Stock.  Holders  of  Warrants  who do not
complete the Series B Exercise  prior to June 11, 1998 forfeit any right to make
the Series C Exercise  under the  Warrant.  The  Company  has the right,  at its
option,  to convert a Series B or Series C Exercise  into a "cashless"  exercise
based on the value of a Series B or Series C Exercise  (equal to the fair market
value per share of the Common Stock less the exercise  price per share)  divided
by the market price of the Common  Stock at the time of  exercise.  Prior to the
purchase of Common Stock upon the exercise of a Warrant, the holder of a Warrant
will have none of the rights or privileges of a stockholder of the Company.  The
holders of Warrants outstanding as of May 15, 1998 have the right to purchase an
aggregate of


                                      -14-

<PAGE>



1,349,000 shares of Common Stock upon the Series B Exercise, and an aggregate of
1,844,000  shares of Common Stock upon the Series C Exercise  (assuming the full
exercise of the Series B Exercise by the holders of outstanding Warrants).

CONTINGENT STOCK RIGHTS

         In connection  with the Triplex merger,  the Company issued  contingent
rights (the "Triplex  Contingent Stock Rights") to the former holders of Triplex
stock and options  entitling them to receive  additional  shares of Common Stock
upon the occurrence of certain  events.  The remaining  rights under the Triplex
Contingent  Stock Rights  entitle the former Triplex stock and option holders to
receive  shares of Common Stock with an aggregate  fair market value at the time
of issuance of $5.0  million  (subject  to certain  adjustments)  if the Company
obtains data from clinical trials of ZintevirTM on or before  September 11, 2000
that the  Company's  Board of Directors  determines  to be sufficient to file an
NDA. In no event,  however,  shall more than  2,189,506  shares of Common  Stock
(subject  to  adjustments  in the  event of stock  splits,  stock  dividends  or
reclassification of the Common Stock) be issued pursuant to the remaining rights
under the Triplex Contingent Stock Rights.

CERTAIN PROVISIONS OF THE COMPANY'S CHARTER AND BYLAWS AND DELAWARE LAW

         Certain  provisions of the Certificate of Incorporation  and Bylaws are
intended to enhance the  likelihood of continuity  and stability in the Board of
Directors  of the  Company  and in its  policies,  but might  have the effect of
delaying  or  preventing  a change in control of the  Company  and may make more
difficult the removal of incumbent management even if such transactions could be
beneficial  to the  interests  of  stockholders.  Set  forth  below is a summary
description of such provisions:

         Authority  to Issue  Preferred  Stock.  The  Company's  Certificate  of
Incorporation  authorizes the Board of Directors,  without stockholder approval,
to establish and to issue shares of one or more series of preferred stock,  each
such series having such voting rights, dividend rates, liquidation,  redemption,
conversion and other rights as may be fixed by the Board.

         Stockholder  Actions and  Meetings.  The  Company's  Bylaws direct that
special  meetings  of the  stockholders  may only be called by a majority of the
members of the Board of Directors,  the Chairman of the Board of Directors,  the
President of the Company or the holders of not less than 30 percent of the total
voting power of all shares of the Company's  capital  stock  entitled to vote in
the  election  of  directors.  The Bylaws  further  provide  that  stockholders'
nominations to the Board of Directors and other stockholder business proposed to
be transacted at stockholder  meetings must be timely received by the Company in
a proper  written  form which meets the  prescribed  content  requirements.  The
Certificate of  Incorporation  and Bylaws of the Company  prohibit  stockholders
from taking any action by written consent.

         Classification of Directors. The Company's Certificate of Incorporation
and Bylaws provide that the directors of the Company shall be divided into three
classes as equal in number as possible serving three-year terms.

         Limitation  of Director  Liability.  Section  102(b)(7) of the Delaware
General Corporation Law ("Section 102(b)")  authorizes  corporations to limit or
eliminate  the  personal  liability  of  directors  to  corporations  and  their
stockholders  for monetary  damages for breach of directors'  fiduciary  duty of
care.  Although  Section  102(b)  does not change  directors'  duty of care,  it
enables  corporations  to limit available  relief to equitable  remedies such as
injunction or rescission.  The Company's Certificate of Incorporation limits the
liability of directors to the Company or its  stockholders (in their capacity as
directors but not in their capacity as officers) to the fullest extent permitted
by Section 102(b). Specifically, directors of the Company will not be personally
liable for  monetary  damages  for breach of a  director's  fiduciary  duty as a
director,  except for liability:  (i) for any breach of the  director's  duty of
loyalty to the Company or its  stockholders,  (ii) for acts or omissions  not in
good faith or which involve  intentional  misconduct  or a knowing  violation of
law, (iii) for unlawful  payments of dividends or unlawful stock  repurchases or
redemptions as provided in Section 174 of the Delaware  General  Corporation Law
or (iv) for any transaction from which the director derived an improper personal
benefit.



                                      -15-

<PAGE>



         Indemnification.  To the maximum extent permitted by law, the Company's
Certificate of Incorporation and Bylaws provide for mandatory indemnification of
directors,  and permit indemnification of officers,  employees and agents of the
Company against all expense, liability and loss to which they may become subject
or which they may incur as a result of being or having been a director, officer,
employee or agent of the  Company.  In  addition,  the Company  must  advance or
reimburse directors, and may advance or reimburse officers, employees and agents
for expenses incurred by them in connection with indemnifiable claims.

         Section 203 of the Delaware  General  Corporation  Law ("Section  203")
generally  provides  that a  stockholder  acquiring  more than 15 percent of the
outstanding voting stock of a corporation subject to the statute (an "Interested
Stockholder")  but less than 85  percent of such stock may not engage in certain
"Business  Combinations"  with the corporation for a period of three years after
the date on which the stockholder  became an Interested  Stockholder  unless (i)
prior to such date, the  corporation's  board of directors  approved  either the
Business  Combination  or the  transaction  in which the  stockholder  became an
Interested  Stockholder,  or (ii) the  Business  Combination  is approved by the
corporation's board of directors and authorized at a stockholders'  meeting by a
vote of at least two-thirds of the  corporation's  outstanding  voting stock not
owned by the Interested Stockholder.  Under Section 203, these restrictions will
not apply to certain Business Combinations proposed by an Interested Stockholder
following  the earlier of the  announcement  or  notification  of one of certain
extraordinary transactions involving the corporation and a person who was not an
Interested  Stockholder  during  the  previous  three  years  or who  became  an
Interested   Stockholder  with  the  approval  of  the  corporation's  board  of
directors,  if such  extraordinary  transaction  is approved or not opposed by a
majority of the directors  who were  directors  prior to any person  becoming an
Interested  Stockholder  during the previous three years or were recommended for
election or elected to succeed such directors by a majority of such directors.

         Section 203 defines the term "Business Combination" to encompass a wide
variety of transactions with or caused by an Interested  Stockholder,  including
transactions  in which the  Interested  Stockholder  receives or could receive a
benefit on other than a pro rata basis with other stockholders, such as mergers,
certain asset sales,  certain  issuances of additional  shares to the Interested
Stockholder,  transactions with the corporation which increase the proportionate
interest in the  corporation  directly  or  indirectly  owned by the  Interested
Stockholder,  or  transactions  in which  the  Interested  Stockholder  receives
certain other benefits.

         The  provisions  of  Section  203,  together  with the  ability  of the
Company's   Board  of  Directors  to  issue   Preferred  Stock  without  further
stockholder action,  could delay or frustrate the removal of incumbent directors
or a change in control of the Company.  The  provisions  also could  discourage,
impede or prevent a merger,  tender offer or proxy  contest,  even if such event
would be favorable to the interests of stockholders. The Company's stockholders,
by adopting an  amendment  to the  Company's  Certificate  of  Incorporation  or
Bylaws,  may elect not to be governed by Section 203  effective  12 months after
such adoption.  Neither the Company's  Certificate of  Incorporation  nor Bylaws
currently exclude the Company from the restrictions imposed by Section 203.

TRANSFER AGENT

         The transfer  agent and  registrar for the Common Stock and Warrants is
American Stock Transfer & Trust Company.

REGISTRATION RIGHTS

         The Company entered into registration rights agreements dated September
1, 1986 with Dr. Jim Klostergaard and Dr. Gabriel  Lopez-Berestein.  Pursuant to
such  Agreements,   Drs.   Klostergaard  and   Lopez-Berestein   have  unlimited
"piggyback" registration rights with respect to the shares of Common Stock owned
by them.  These  registration  rights  are  subject to  certain  conditions  and
limitations,  including the right of the  underwriters to restrict the number of
shares offered in a registration.

         Pursuant  to a  registration  rights  agreement  dated  August 2, 1989,
holders of  approximately  1,823,783  shares of Common  Stock and of warrants to
purchase  60,623  shares  of Common  Stock  have the right to demand up to three
registrations  of the  Registrable  Securities (as defined) under the Securities
Act and unlimited piggyback registration


                                      -16-

<PAGE>



rights.  These demand  registration rights are subject to certain conditions and
limitations,  including  the right of the  underwriters  to limit the  number of
shares  offered  in such  registration  and to  require a lock-up  of shares not
included  in  such  registration  and the  right  of the  Company  to  refuse  a
registration under certain conditions,  such as the six-month period immediately
following  effectiveness of a registration  statement and the ninety-day  period
preceding  an  expected  filing  of a  registration  statement.  If the  Company
proposes an offering of  Registrable  Securities,  either for its own account or
for other stockholders exercising such registration rights, the other holders of
these  rights are  entitled to notice of the  contemplated  registration  and an
opportunity to include their securities in such  registration.  The Company must
use its best  efforts to effect such  registration,  with  certain  limitations.
Furthermore,  the  Company  is  required  to  pay  the  associated  registration
expenses,  excluding the underwriting  discounts and sales commissions,  for the
holders exercising such registration rights.

         In   addition,   Genzyme   Corporation   ("Genzyme")   has  one  demand
registration  right, which requires the Company to register all shares of Common
Stock Genzyme currently holds or may acquire in the future.

         In connection with the Triplex  merger,  the Company granted the former
stockholders of Triplex unlimited  piggyback  registration  rights which provide
that, if the Company  proposes an offering of Common  Stock,  either for its own
account or for other stockholders exercising registration rights, the holders of
the  rights  are  entitled  to notice of the  contemplated  registration  and an
opportunity  to include  their  Common  Stock in such  registration,  subject to
certain limitations.

                              PLAN OF DISTRIBUTION

         The  Shares  offered  hereby  are  issuable  upon the  exercise  of the
Warrants and the payment of the exercise price for the Series B Exercise and the
Series C Exercise, respectively. The exercise price of the Series B Exercise and
the Series C Exercise  and the number of Shares  issuable  upon the  exercise of
each  Warrant are subject to  adjustment,  as  provided  in the  Warrants,  upon
certain events.

         In accordance with the provisions of the Warrants, upon the delivery of
a  written  notice  in the  form of the  subscription  notice  set  forth in the
Warrants  (and,  upon  exercise of the Series C Exercise,  the  surrender of the
Warrant),  duly  executed,  along with payment in full of the exercise price for
the Series B Exercise or Series C  Exercise,  as the case may be, to the warrant
agent  or its  successor  at its  principal  office  in New  York  City,  Aronex
Pharmaceuticals  will  issue the  applicable  number of shares of Common  Stock,
registered  in such name or names as may be directed  by him, to the  registered
holder of such Warrant or Warrants.

                                 USE OF PROCEEDS

         The  Company  intends to use the  proceeds  from the sale of the shares
upon  exercise of the Warrants to fund its research and  development  activities
and  for  general  corporate  purposes,  depending  on the  Company's  needs  as
determined from time to time by the Company's Board of Directors.

                                    DILUTION

         The net  tangible  book value of the Common  Stock of the Company as of
March 31, 1998 was  approximately  $22.6  million,  or  approximately  $1.46 per
share.  Net tangible book value per share of Common Stock  represents  the total
tangible assets of the Company  reduced by its total  liabilities and divided by
the number of shares of Common Stock outstanding. If the holders of all Warrants
outstanding  as of March 31, 1998 had exercised the Series B Exercise and Series
C Exercise as of such date at the Series B Exercise price of $8.00 per share and
the Series C Exercise  price of $12.00 per  share,  the  adjusted  pro forma net
tangible  book value of the  Common  Stock of the  Company as of March 31,  1998
would have been  approximately  $55.5 million or approximately  $2.97 per share.
The increase in net  tangible  book value of $1.51 per share would be due solely
to the  purchase  of the  Shares.  Holders of  Warrants  would have  immediately
incurred a dilution of $5.03 per share and $9.03 per share upon the  exercise of
the Series B Exercise  and the Series C Exercise,  respectively.  "Dilution"  is
determined by subtracting pro forma net tangible book value per share


                                      -17-

<PAGE>



after the  exercise  of the Series B Exercise  and the Series C Exercise  of all
Warrants from the exercise price of the Series B Exercise and Series C Exercise,
respectively.

                                  LEGAL MATTERS

         Andrews & Kurth L.L.P.  has passed upon certain  matters as counsel for
the Company.

                                     EXPERTS

         The financial  statements  included in the  Company's  Annual Report on
Form 10-K for the year ended December 31, 1997 and  incorporated by reference in
this  Prospectus have been audited by Arthur  Andersen LLP,  independent  public
accountants,  as  indicated  in  their  report  with  respect  thereto,  and are
incorporated by reference  herein in reliance upon the authority of said firm as
experts in giving said report.



                                      -18-

<PAGE>



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


No  dealer,  salesperson  or  other  person  has  been  authorized  to give  any
information  or to make any  representations  other than those  contained  in or
incorporated  by reference in this  Prospectus in connection with the offer made
by this Prospectus and, if given or made,  such  information or  representations
must not be relied upon as having been authorized.  Neither the delivery of this
Prospectus nor any sale made hereunder shall,  under any  circumstances,  create
any  implication  that there has been no change in the  affairs  of the  Company
since  the  date  hereof.  This  Prospectus  does  not  constitute  an  offer or
solicitation  by anyone in any  jurisdiction in which such offer or solicitation
is not  authorized  or in which the person making such offer is not qualified to
do so or to any person to whom it is unlawful to make such solicitation.




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




                  TABLE OF CONTENTS

                                                Page
                                                ----

Available Information........................     2
Documents Incorporated by Reference..........     2
The Company..................................     4
Risk Factors.................................     5
Description of the Company's Securities......    14
Plan of Distribution.........................    17
Use of Proceeds..............................    17
Dilution.....................................    17
Legal Matters................................    18
Experts......................................    18




[ARONEX PHARMACEUTICALS, INC.]


     3,193,000 Shares of
        Common Stock
Issuable Upon Exercise of Warrants



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

          PROSPECTUS

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





    Dated May 20, 1998



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


<PAGE>                                                  


                                     PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14.   Other Expenses of Issuance and Distribution

         Set forth below are the expenses  expected to be incurred in connection
with the issuance and distribution of the securities registered hereby. With the
exception  of the  Securities  and  Exchange  Commission  registration  fee, the
amounts  set forth  below are  estimates  and  consist  exclusively  of expenses
incurred in connection with this amendment on Form S-3:


Securities and Exchange Commission 
 registration fee.................................................. $   --   (1)
Printing and engraving expenses....................................     4,000
Legal fees and expenses............................................     5,000
Accounting fees and expenses.......................................     5,000
Blue Sky fees and expenses.........................................       --
Miscellaneous expenses.............................................     1,000
                                                                    ---------
         Total..................................................... $  15,000
                                                                    =========
                                                  

- ---------------------------
(1)      Previously  paid  in  connection  with  the  filing  of  the  Company's
         Registration  Statement  on  Form  S-4  to  which  this  post-effective
         amendment relates.

ITEM 15.   INDEMNIFICATION OF DIRECTORS AND OFFICERS

         Section 145 of the Delaware  General  Corporation  Law ("DGCL"),  inter
alia,  empowers a Delaware  corporation  to indemnify any person who was or is a
party  or is  threatened  to be  made a  party  to any  threatened,  pending  or
completed action, suit or proceeding (other than an action by or in the right of
the  corporation)  by reason of the fact that such  person is or was a director,
officer,  employee  or agent of the  corporation,  or is or was  serving  at the
request of the corporation as a director,  officer, employee or agent of another
corporation or other enterprise,  against expenses (including  attorneys' fees),
judgments, fines and amounts paid in settlement actually and reasonably incurred
by him in  connection  with such action,  suit or proceeding if he acted in good
faith and in a manner he reasonably believed to be in or not opposed to the best
interests  of the  corporation,  and,  with  respect to any  criminal  action or
proceeding, had no reasonable cause to believe his conduct was unlawful. Similar
indemnity is authorized for such persons against expenses (including  attorneys'
fees)  actually  and  reasonably  incurred  in  connection  with the  defense or
settlement of any such  threatened,  pending or completed action or suit if such
person  acted in good faith and in a manner he  reasonably  believed to be in or
not opposed to the best interests of the corporation,  and provided further that
(unless a court of competent  jurisdiction otherwise provides) such person shall
not have been adjudged liable to the corporation.  Any such  indemnification may
be made only as authorized in each  specific  case upon a  determination  by the
stockholders  or  disinterested  directors or by independent  legal counsel in a
written  opinion that  indemnification  is proper because the indemnitee has met
the applicable standard of conduct.

         Section 145 further  authorizes a corporation  to purchase and maintain
insurance on behalf of any person who is or was a director, officer, employee or
agent of the corporation, or is or was serving at the request of the corporation
as a director,  officer, employee or agent of another corporation or enterprise,
against  any  liability  asserted  against  him and  incurred by him in any such
capacity,  or arising out of his status as such,  whether or not the corporation
would  otherwise  have the power to indemnify him under Section 145. The Company
maintains  policies  insuring its and its  subsidiaries'  officers and directors
against  certain  liabilities  for actions taken in such  capacities,  including
liabilities under the Securities Act of 1933, as amended (the "Securities Act").



                                      II-1

<PAGE>



         Article VIII of the Amended and Restated  Certificate of  Incorporation
of the  Company  and  Article  VII of the  Bylaws  of the  Company  provide  for
indemnification  of the directors of the Company to the full extent permitted by
law, as now in effect or later  amended.  Article VII of the Bylaws also permits
the  indemnification to the same extent of officers,  employees or agents of the
Company  if,  and to the  extent,  authorized  by the  Board  of  Directors.  In
addition, the Bylaws provide for indemnification  against expenses incurred by a
director to be paid by the  Company at  reasonable  intervals  in advance of the
final  disposition  of  such  action,  suit or  proceeding  upon  receipt  of an
undertaking  by or on behalf of the  director or officer to repay such amount if
it shall be ultimately  determined  that he is not entitled to be indemnified by
the Company. The Bylaws further provide for a contractual cause of action on the
part of directors of the Company for  indemnification  claims that have not been
paid by the Company.

         The Company also has provided liability insurance for each director and
officer for certain  losses  arising  from claims or charges  made  against them
while acting in their capacities as directors or officers of the Company.

         Article  VII of the  Company's  Amended  and  Restated  Certificate  of
Incorporation,  as amended,  limits under certain circumstances the liability of
the Company's directors for a breach of their fiduciary duty as directors. These
provisions  do not eliminate the liability of a director (i) for a breach of the
director's duty of loyalty to the Company or its stockholders,  (ii) for acts or
omissions not in good faith or that involve intentional  misconduct or a knowing
violation  of  law,  (iii)  under  Section  174 of  the  DGCL  (relating  to the
declaration  of dividends  and purchase or  redemption of shares in violation of
the  DGCL) or (iv) for any  transaction  from  which  the  director  derived  an
improper personal benefit.

ITEM 16.   EXHIBITS


          4.1     Form of Common Stock Certificate (incorporated by reference to
                  Exhibit 4.1 to the Company's Quarterly Report on Form 10-Q for
                  the quarterly period ended June 30, 1996).
         *4.2     Form of Warrant Certificate
         *5.1     Opinion of Porter & Hedges
         *8.1     Opinion of Porter & Hedges
         23.1     Consent of Arthur Andersen LLP
        *23.2     Consent of Porter & Hedges
         25.1     Powers of Attorney, included in Part II of this Post-Effective
                  Amendment No. 2 to the Registration Statement

- ---------------------------
* Previously filed


                                      II-2

<PAGE>



ITEM 17.   UNDERTAKINGS

                  (1)      The undersigned registrant hereby undertakes:

                  (a) To file,  during any  period in which  offers or sales are
         being made, a post-effective amendment to this registration statement:

                           (i) To include  any  prospectus  required  by Section
                  10(a)(3)  of the  Securities  Act of  1933,  as  amended  (the
                  "Securities Act");

                           (ii) To reflect in the prospectus any facts or events
                  arising after the effective date of the Registration Statement
                  (or the most recent  post-effective  amendment thereof) which,
                  individually  or in the  aggregate,  represent  a  fundamental
                  change  in the  information  set  forth  in  the  Registration
                  Statement.  Notwithstanding  the  foregoing,  any  increase or
                  decrease in volume of securities  offered (if the total dollar
                  value of  securities  offered  would not exceed that which was
                  registered)  and any deviation from the low or high end of the
                  estimated  maximum offering range may be reflected in the form
                  of  prospectus  filed  with the  Commission  pursuant  to Rule
                  424(b) (ss.  230.424(b) of this chapter) if, in the aggregate,
                  the changes in volume and price  represent  no more than a 20%
                  change in the maximum  aggregate  offering  price set forth in
                  the  "Calculation of Registration  Fee" table in the effective
                  registration statement;

                           (iii)  To  include  any  material   information  with
                  respect to the plan of distribution  not previously  disclosed
                  in this Registration  Statement or any material change to such
                  information in the Registration Statement.

                  (b) That, for the purpose of determining  any liability  under
         the Securities Act of 1933, each such post-effective amendment shall be
         deemed to be a new  registration  statement  relating to the securities
         offered therein, and the offering of such securities at that time shall
         be deemed to be the initial bona fide offering thereof.

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

                  (2) The undersigned  registrant  hereby  undertakes  that, for
purposes of determining  any liability  under the  Securities Act of 1933,  each
filing of the  registrant's  annual report  pursuant to section 13(a) or section
15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing
of an employee  benefit  plan's annual  report  pursuant to section 15(d) of the
Securities  Exchange  Act of 1934)  that is  incorporated  by  reference  in the
registration  statement  shall  be  deemed  to be a new  registration  statement
relating to the securities offered therein,  and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

                  (3) Insofar as indemnification  for liabilities  arising under
the  Securities  Act of  1933  may  be  permitted  to  directors,  officers  and
controlling persons of the registrant pursuant to the foregoing  provisions,  or
otherwise, the registrant has been advised that in the opinion of the Securities
and  Exchange  Commission  such  indemnification  is  against  public  policy as
expressed in the Act and is, therefore, unenforceable. In the event that a claim
for  indemnification  against  such  liabilities  (other than the payment by the
registrant  of expenses  incurred by paid by a director  officer or  controlling
person in the successful defense of any action,  suit or proceeding) is asserted
by  such  director,  officer  or  controlling  person  in  connection  with  the
securities being  registered,  the registrant will, unless in the opinion of its
counsel the matter has been settled by controlling precedent,  submit to a court
of appropriate  jurisdiction  the question whether such  indemnification  by its
against  public policy as expressed in the Act and will be governed by the final
adjudication of such issue.



                                      II-3

<PAGE>



                                   SIGNATURES

         Pursuant to the  requirements  of the Securities  Exchange Act of 1933,
the Registrant certifies that is has reasonable grounds to believe that it meets
all of the  requirements  for  filing  on  Form  S-3 and has  duly  caused  this
Registration Statement to be signed on its behalf by the undersigned,  thereunto
duly authorized, in the City of The Woodlands, State of Texas on the 18th day of
May, 1998.

                                         ARONEX PHARMACEUTICALS, INC.


                                         By: /s/  Geoffrey F. Cox
                                            ------------------------------------
                                               Geoffrey F. Cox
                                               Chairman of the Board and 
                                                 Chief Executive Officer

         KNOW ALL MEN BY THESE PRESENTS,  that each of the undersigned  officers
and directors of Aronex Pharmaceuticals, Inc. (the "Company") hereby constitutes
and  appoints  Geoffrey F. Cox and Terance A.  Murnane,  or either of them (with
full power to each of them to act alone),  his true and lawful  attorney-in-fact
and agent,  with full power of substitution and  resubstitution,  for him and on
his behalf and in his name, place and stead, in any and all capacities, to sign,
execute and file this  Registration  Statement under the Securities Act of 1933,
as  amended,  and  any  or  all  amendments   (including,   without  limitation,
post-effective amendments), with all exhibits and any and all documents required
to be filed with respect thereto, with the Securities and Exchange Commission or
any regulatory authority,  granting unto such  attorneys-in-fact and agents, and
each of them acting  alone,  full power and authority to do and perform each and
every act and thing requisite and necessary to be done in and about the premises
in order to  effectuate  the same,  as fully to all intents  and  purposes as he
himself might or could do if personally present, hereby ratifying and confirming
all that such  attorneys-in-fact and agents, or any of them, or their substitute
or substitutes, may lawfully do or cause to be done.

         PURSUANT  TO THE  REQUIREMENTS  OF THE  SECURITIES  ACT OF  1933,  THIS
REGISTRATION  STATEMENT  HAS  BEEN  SIGNED  BY  THE  FOLLOWING  PERSONS  IN  THE
CAPACITIES AND ON THE DATES INDICATED.

<TABLE>
<CAPTION>

                 Signature                                       Title                                Date
                 ---------                                       -----                                ----

<S>                                                  <C>                                         <C>    
/s/ Geoffrey F. Cox
- ------------------------------------                   Chairman of the Board and                  May 18, 1998
Geoffrey F. Cox                                         Chief Executive Officer
                                                      (Principal Executive Officer)
/s/ Terance A. Murnane  
- ------------------------------------                           Controller                         May 18, 1998
Terance A. Murnane                            (Principal Financial and Accounting Officer)
                                                                Director                          May 18, 1998
                                                                
 /s/ Gabriel Lopez-Berestein                                    Director                          May 18, 1998
- ------------------------------------
Gabriel Lopez-Berestein
                                                                                         
/s/ Ronald J. Brenner, Ph.D.                                    Director                          May 18, 1998
- ------------------------------------ 
Ronald J. Brenner, Ph.D.
                                                                                                                             
/s/ James R. Butler                                             Director                          May 18, 1998 
- ------------------------------------
James R. Butler

/s/ Martin P. Sutter                                            Director                          May 18, 1998
- ------------------------------------ 
Martin P. Sutter
                                                                  
/s/ Gregory F. Zaic                                             Director                          May 18, 1998
- ------------------------------------ 
Gregory F. Zaic

</TABLE>


                                      II-4

<PAGE>



                                INDEX TO EXHIBITS



                                                                         
Number                               Description          
- ------                               -----------          
                                                            

  4.1     Form of Common Stock Certificate (incorporated by reference to Exhibit
          4.1 to the  Company's  Quarterly Report on Form 10-Q for the quarterly
          period ended June 30, 1996)
 *4.2     Form of Warrant Certificate
 *5.1     Opinion of Porter & Hedges
 *8.1     Opinion of Porter & Hedges
 23.1     Consent of Arthur Andersen LLP
*23.2     Consent of Porter & Hedges
 25.1     Powers of Attorney, included in Part II of this Post-Effective 
          Amendment No. 1 to the Registration Statement

- ---------------------------
*Previously filed.





                                                               EXHIBIT 23.1


                    CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS


As independent  public  accountants,  we hereby consent to the  incorporation by
reference in this Post-Effective  Amendment No. 2 to the Registration  Statement
on Form S-3 of our report dated  February 17, 1998 included in the Annual Report
Form 10-K for the year ended December 31, 1997 of Aronex  Pharmaceuticals,  Inc.
and to all references to our Firm included in this Registration Statement.




ARTHUR ANDERSEN LLP



The Woodlands, Texas
May 19, 1998



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