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                              [NEXSTAR LETTERHEAD]

FOR IMMEDIATE RELEASE
Contacts at NeXstar Pharmaceuticals:           Glaxo Wellcome:
Anna Sussman                                   Nancy Pekarek
Manager, Investor Relations                    Group Public Affairs
303-546-7875                                   011-44-171-493-4060

                     GLAXO WELLCOME, NEXSTAR PHARMACEUTICALS
           SIGN THREE-PART COLLABORATION FEATURING THE SELEX PROCESS;
                 NEXSTAR LICENSES A GLAXO WELLCOME ONCOLOGY DRUG

     BOULDER, COLO., May 27, 1998--NeXstar Pharmaceuticals, Inc. (NASDAQ: NXTR)
and Glaxo Wellcome (LSE: GLXO) announced today a three-part collaboration,
including a license by Glaxo Wellcome for the use of NeXstar Pharmaceuticals'
proprietary SELEX drug discovery process as a research tool for target
validation in Glaxo Wellcome's functional genomics programs.

The three primary components of the collaboration are:

o    Glaxo Wellcome receives a non-exclusive right to practice NeXstar
     Pharmaceuticals' proprietary SELEX process for target validation;

o    NeXstar Pharmaceuticals receives the exclusive rights to develop and
     commercialize a liposomal formulation of Glaxo Wellcome's proprietary
     topoisomerase I inhibitor (lurtotecan), a compound that has completed Phase
     II clinical trials for the treatment of various cancers in its
     non-liposomal form; and

o    a $10 million equity investment by Glaxo Wellcome in NeXstar
     Pharmaceuticals.

Detailed financial terms of the collaboration were not disclosed.

"This is clearly a very important relationship for us, and we are pleased with
the scale and scope of our interactions with Glaxo Wellcome," said Patrick J.
Mahaffy, president and CEO of NeXstar Pharmaceuticals. "The desire of Glaxo
Wellcome to utilize the SELEX technology for target validation in their global
research labs highlights the potential for aptamers to significantly speed up
and improve drug discovery and development programs. We are also very
enthusiastic about the opportunity to develop liposomal lurtotecan and the role
that this product may play in our growing oncology portfolio. As represented by
this license and their equity investment, the confidence expressed by Glaxo
Wellcome in both our formulation and development skills is a further example of
our growth as an organization."

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NEXSTAR, GLAXO SIGN COLLABORATION -- PAGE 2

THE SELEX PROCESS FOR TARGET VALIDATION

NeXstar Pharmaceuticals has been developing the SELEX process over the past
several years. The SELEX process is a combinatorial chemistry technology which
allows for the very rapid identification of potent and specific inhibitors of
targets involved in the development or progression of disease. The compounds
identified by the SELEX process are called aptamers. In addition to their
potential direct role as novel therapeutics, aptamers can be used in preclinical
disease models to assess the potential therapeutic benefit of altering the
activity of a specific target molecule and ultimately to confirm the role of the
target molecule prior to initiation of small molecule or other drug discovery
programs.

Under the SELEX license to Glaxo Wellcome, the SELEX technology will be used as
a research tool to enhance Glaxo Wellcome's functional genomics efforts. Glaxo
Wellcome will use aptamers to identify which genes or gene products are critical
to disease progression and which make good targets for drug discovery. Glaxo
Wellcome researchers will then have the ability to make more informed choices
for their drug discovery programs.

In addition to the research license, the SELEX license grants Glaxo Wellcome
certain rights to develop aptamers as therapeutics. In turn, Glaxo Wellcome
would make milestone and royalty payments to NeXstar Pharmaceuticals for the
development of such aptamers.

"Glaxo Wellcome is committed to developing innovative new medicines through the
application of knowledge derived from our genomics programs," said Dr. Mark
Payton, director of cellular sciences, Glaxo Wellcome Research and Development,
UK. "We are very excited about working with aptamers derived from the SELEX
process. They will become a valuable new tool helping us to prioritize new drug
targets in a number of our key disease areas."

"This is a tremendous confirmation of NeXstar Pharmaceuticals' proprietary SELEX
technology as a rapid, innovative method of target validation," said Larry M.
Gold, Ph.D., chairman and chief scientific officer of NeXstar Pharmaceuticals.
"Our technology can be a very significant complement to genomics programs and
allow for the better selection of molecular targets for drug discovery and
development that have been validated by aptamers in preclinical models."

TOPOISOMERASE I INHIBITOR (LURTOTECAN)
The second component of the collaboration grants NeXstar Pharmaceuticals the
exclusive license to develop Glaxo Wellcome's proprietary topoisomerase I
inhibitor, known as lurtotecan. Glaxo Wellcome has completed a large Phase II
program with lurtotecan showing encouraging anti-tumor activity.


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NEXSTAR, GLAXO SIGN COLLABORATION -- PAGE 3

NeXstar Pharmaceuticals has produced a liposomal formulation of lurtotecan,
called NX 211. Several preclinical studies have been conducted with NX 211 to
evaluate its efficacy, toxicity and pharmacokinetics (the way the drug behaves
in the body). NX 211 had a three-fold increase in therapeutic index as compared
to the conventional drug. These studies showed that the plasma half life (a
measure of circulation time) and the area under the curve (a measure of drug
exposure) of NX 211 are significantly increased as compared to the conventional
drug. As a result, the potential exists for NX 211 to be more effective and less
toxic than lurtotecan and other topoisomerase inhibitors. Initial plans to
develop the drug include studies to evaluate its effectiveness against ovarian
cancer and a variety of other tumor types. Phase I clinical studies for NX 211
are expected to begin within the next twelve months.

"We believe that by encapsulating lurtotecan into a liposome we have enhanced
the therapeutic potential of the product as a broad spectrum oncology product,"
said Nicole Onetto, M.D., vice president of medical affairs for NeXstar
Pharmaceuticals. "Through the development of the company's other liposomal
products, we have gained a valuable understanding of how a liposome can improve
a variety of drugs, which in their traditional form would be clinically limited
by prohibitive toxicity or inconvenient dosing regimens."

The lurtotecan license requires NeXstar Pharmaceuticals to make certain
milestone and royalty payments to Glaxo Wellcome. In addition, the license
provides Glaxo Wellcome with the opportunity to participate in the further
development of the product in exchange for a licensing fee and sharing in
additional development costs. In certain territories, if Glaxo Wellcome
exercises this option, the companies would co-promote the drug and share in the
profits. In this case, NeXstar Pharmaceuticals would pay no milestones or
royalties to Glaxo Wellcome.

EQUITY INVESTMENT

The third component of this collaboration provides for a $10 million equity
investment by Glaxo Wellcome in the common stock of NeXstar Pharmaceuticals.
Glaxo Wellcome purchased 962,117 shares of NeXstar common stock for $10.39 per
share under the terms of the agreement, which price represented the average of
the daily closing price of NeXstar Pharmaceuticals common stock over the past 30
trading days on which the stock traded.

"The equity investment into NeXstar Pharmaceuticals by Glaxo Wellcome validates
our organization and its commercial prospects," Mahaffy said. "We believe that
these agreements will be the basis of a long and profitable relationship with
Glaxo Wellcome."

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NEXSTAR, GLAXO SIGN COLLABORATION -- PAGE 4

This press release contains forward-looking statements that involve risks and
uncertainties, and actual events or results may differ materially. These
statements concern, among other things, NeXstar Pharmaceuticals' goals
concerning the future clinical prospects for NX 211 and products created using
the SELEX process. While these statements reflect NeXstar Pharmaceuticals' best
current judgment, they are subject to risks and uncertainties that could cause
actual results to vary from current projections. These risk factors are
identified in the company's reports to the Securities and Exchange Commission
filed on Forms 10-K and 10-Q, and in other SEC filings.

NeXstar Pharmaceuticals, Inc. is an integrated biopharmaceutical company engaged
in the discovery, development, manufacture and commercialization of products to
treat serious and life-threatening illnesses. The company currently markets two
drugs in the United States and around the world, AmBisome and DaunoXome. Based
in Boulder, Colo., NeXstar Pharmaceuticals maintains additional research,
development and manufacturing facilities in San Dimas, Calif., and marketing
subsidiaries worldwide.

Glaxo Wellcome is a research-based company whose people are committed to
fighting disease by bringing innovative medicines and services to patients
throughout the world and the healthcare providers who serve them.

NOTE: This press release is available at www.nexstar.com/Press_Releases/
PR98.htm.


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