Exhibit 99.1


                      LA JOLLA PHARMACEUTICAL TO PRESENT AT
                  7TH INTERNATIONAL CONGRESS ON SYSTEMIC LUPUS
                      ERYTHEMATOSUS AND RELATED CONDITIONS

SAN DIEGO, APRIL 21, 2004 - La Jolla Pharmaceutical Company (Nasdaq: LJPC) today
announced that it will present results from its clinical trials of Riquent(R)
(abetimus sodium, formerly known as LJP 394) for the treatment of lupus renal
disease during the 7th International Congress on Systemic Lupus Erythematosus
(SLE) and Related Conditions. The conference will take place May 10-13, 2004 at
the Hilton New York Hotel in New York City. For additional information on the
conference, please visit http://lupus2004.org.

The 7th International Congress on SLE and Related Conditions will be attended by
more than 3,000 clinicians and scientists from around the world who will meet to
discuss the latest research about lupus, an autoimmune disease that affects more
than one million patients in the United States and Europe. Existing treatments
for lupus can cause severe side effects, and no new drugs have been approved in
the United States to treat this disease in more than 30 years.

"We are pleased to be a part of this important event, which brings together
leading lupus clinicians, advocacy organizations, pharmaceutical companies and
patients to review the latest lupus research," said Steve Engle, Chairman and
CEO of La Jolla Pharmaceutical Company.

Matthew Linnik, Ph.D., La Jolla Pharmaceutical Company's Chief Scientific
Officer and Executive Vice President of Research, will give an oral presentation
entitled "Anti-dsDNA Antibodies and Exacerbation of Renal Disease in Patients
with Systemic Lupus Erythematosus: Results from Two Randomized Controlled Trials
with LJP 394" on Thursday, May 13, 2004 at 10:30 a.m.

In addition, three posters on Riquent will be presented on Tuesday, May 11,
2004:

      -     "Reductions in 24 Hour Urine Protein Levels Associated with
            Treatment of Lupus Patients with LJP 394 in Two Randomized, Placebo
            Controlled, Double-Blind Clinical Trials"

      -     "Improved Health-Related Quality of Life (HRQOL) Following Sustained
            Reductions in Anti-dsDNA Antibodies in Patients with Systemic Lupus
            Erythematosus After Treatment with LJP 394"

      -     "Summary of Safety Results from Studies of LJP 394 in SLE Patients"

La Jolla Pharmaceutical will also participate in two industry panel discussions
hosted by the Lupus Foundation of America during the conference. The first,
entitled "Clinical Advances For Persons With Lupus," will be held on Monday, May
10, 2004 at 9:00 a.m. and the second, entitled "New Treatments for Patients with
SLE: How Are They

Different and How Might They Work?" will be held on Tuesday, May 11, 2004 at
1:30 p.m.

ABOUT LUPUS

Lupus (systemic lupus erythematosus or SLE) is a chronic, potentially
life-threatening autoimmune disease. About 90% of lupus patients are female, and
many develop the disease during their childbearing years. Approximately 50% of
lupus patients have renal disease, which can lead to irreversible kidney damage,
kidney failure and the need for dialysis. Latinos, African Americans and Asians
face an increased risk of serious renal disease associated with lupus. The
current standard of care for lupus renal disease often involves treatment with
high doses of corticosteroids and immunosuppressive drugs that can cause severe
side effects including diabetes, hypertension and sterility, and may leave
patients vulnerable to opportunistic infections.

La Jolla Pharmaceutical Company is a biotechnology company developing
therapeutics for antibody-mediated autoimmune diseases and inflammation
afflicting several million people in the United States and Europe. The Company
is developing Riquent(R) for the treatment of lupus kidney disease, a leading
cause of sickness and death in patients with lupus. The Company is also
developing LJP 1082 for the treatment of antibody-mediated thrombosis, a
condition in which patients suffer from recurrent stroke, deep-vein thrombosis
and other thrombotic events, and is in the early stage of developing small
molecules to treat various other autoimmune and inflammatory conditions. The
Company's common stock is traded on The Nasdaq Stock Market under the symbol
LJPC. For more information about the Company, visit its Web site:
http://www.ljpc.com.

The forward-looking statements in this press release involve significant risks
and uncertainties, and a number of factors, both foreseen and unforeseen, could
cause actual results to differ materially from our current expectations.
Forward-looking statements include those that express a plan, belief,
expectation, estimation, anticipation, intent, contingency, future development
or similar expression. Although our New Drug Application ("NDA") for Riquent(R)
has been accepted by the United States Food and Drug Administration (the "FDA")
for review, there is no guarantee that the FDA will approve Riquent in a timely
manner, or at all. Our analyses of clinical results of Riquent, previously known
as LJP 394, our drug candidate for the treatment of systemic lupus erythematosus
("lupus"), and LJP 1082, our drug candidate for the treatment of
antibody-mediated thrombosis ("thrombosis"), are ongoing and could result in a
finding that these drug candidates are not effective in large patient
populations, do not provide a meaningful clinical benefit, or may reveal a
potential safety issue requiring us to develop new candidates. The analysis of
the data from our Phase 3 trial of Riquent showed that the trial did not reach
statistical significance with respect to its primary endpoint, time to renal
flare, or to the secondary endpoint, time to treatment with high-dose
corticosteroids or cyclophosphamide. Although our NDA for Riquent has been
accepted for review by the FDA, the results from our clinical trials of Riquent
may not ultimately be sufficient to obtain regulatory clearance to market
Riquent either in the United States or Europe, and we may be required to conduct
additional clinical studies

to demonstrate the safety and efficacy of Riquent in order to obtain marketing
approval. There is no guarantee, however, that we will have the necessary
resources to complete any additional trial, that we will elect to conduct an
additional trial, or that any additional trial will sufficiently demonstrate the
safety and efficacy of Riquent. Our blood test to measure the binding affinity
for Riquent is experimental, has not been validated by independent laboratories
and will likely be reviewed as part of the Riquent approval process. Our other
potential drug candidates are at earlier stages of development and involve
comparable risks. Analysis of our clinical trials could have negative or
inconclusive results. Any positive results observed to date may not be
indicative of future results. In any event, regulatory authorities may require
additional clinical trials, or may not approve our drugs. Our ability to develop
and sell our products in the future may be adversely affected by the
intellectual property rights of third parties. Additional risk factors include
the uncertainty and timing of: obtaining required regulatory approvals,
including delays associated with any approvals that we may obtain; the clear
need for additional financing; our ability to pass FDA pre-approval inspections
of our manufacturing facilities and processes; the increase in capacity of our
manufacturing capabilities for possible commercialization; successfully
marketing and selling our products; our lack of manufacturing, marketing and
sales experience; our ability to make use of the orphan drug designation for
Riquent; generating future revenue from product sales or other sources such as
collaborative relationships; future profitability; and our dependence on patents
and other proprietary rights. Readers are cautioned to not place undue reliance
upon forward-looking statements, which speak only as of the date hereof, and we
undertake no obligation to update forward-looking statements to reflect events
or circumstances occurring after the date hereof. Interested parties are urged
to review the risks described in our Annual Report on Form 10-K for the year
ended December 31, 2003, and in other reports and registration statements that
we file with the Securities and Exchange Commission from time to time.

                                       ###