[Letterhead of Triangle Pharmaceuticals, Inc.]

                                               February 16, 1999

To Our Stockholders:

          On January 29, 1999, your Board of Directors declared a dividend 
distribution of Preferred Stock Purchase Rights (the "Rights").  The Rights 
were issued on February 16, 1999 to stockholders of record on that date and 
will expire in ten years.  This letter and its attachment summarize certain 
key features of the Stockholder Rights Plan and the Board of Directors' 
reasons for adopting it.  These documents should be kept with your 
Certificates.

          The Rights contain provisions that should, along with certain 
charter and by-law provisions and certain provisions of the Delaware General 
Corporation Law, help protect the stockholders of Triangle Pharmaceuticals, 
Inc. (the "Company") in the event of an unsolicited attempt to acquire the 
Company, including a gradual accumulation of shares in the open market, a 
partial or two-tier tender offer that does not treat all stockholders 
equally, a squeeze-out merger and other coercive or unfair takeover tactics.  
These tactics can unfairly pressure stockholders, squeeze them out of their 
investment without giving them any real choice and deprive them of the full 
value of their shares, and the Board of Directors does not believe they are 
in the best interests of the Company's stockholders.

          Over 1,700 companies, including approximately half the Fortune 500
companies and two-thirds of the Fortune 200 companies, have issued similar
rights to protect their stockholders against these tactics.  We consider the
Rights to be very valuable in protecting both your right to retain your equity
investment in the Company and the full value of that investment, while not
foreclosing a fair acquisition bid for the Company.

          Your Board of Directors was aware when it acted that some people have
advanced arguments that securities of the sort we are issuing deter legitimate
acquisition proposals.  We carefully considered these views and concluded that
the arguments are speculative and do not justify leaving stockholders without
any protection during the next year.  Your Board of Directors believes that
these Rights represent a sound and reasonable means of addressing the complex
issues of corporate policy.




To Our Stockholders                                                     Page 2
February 16, 1999

          The Rights are not intended to prevent an acquisition of the Company
and will not do so.  However, they should deter any attempt to acquire the
Company in a manner or on terms not approved by the Board of Directors.  The
Rights may be redeemed by the Board of Directors at a price of $.001 per Right
prior to the first public announcement of the accumulation, through open-market
purchases, a tender offer or otherwise, of 15% or more of the combined number of
the Company's shares of Common Stock by a single acquiror or group, and
thereafter in certain circumstances.  Thus, the Rights should not interfere with
any merger or business combination approved by the Board of Directors prior to
that time.

          Issuance of the Rights does not in any way weaken the financial
strength of the Company or interfere with its business plans.  The issuance of
the Rights has no dilutive effect, will not affect reported earnings per share
and will not change the way in which you can presently trade the Company's
shares.

          The Rights will expire February 16, 2009, which should give the
Company adequate time to determine whether any further protection is required.

          The Board of Directors has been advised by legal counsel for the
Company that the distribution of the Rights will not be taxable to you or to the
Company.  However, stockholders may recognize taxable income upon the occurrence
of certain subsequent taxable events.

          In declaring the Rights dividend, we have expressed our confidence in
the future of the Company and our determination that you, our stockholders, be
given every opportunity to participate in that future.

                                        On behalf of the Board of Directors

                                        -------------------------------------
                                        David W. Barry
                                        Chairman and Chief Executive Officer