EXHIBIT 99.1


              LA JOLLA PHARMACEUTICAL DATA ON RIQUENT(R)PRESENTED
                           AT LUPUS MEDICAL CONFERENCE

      7TH INTERNATIONAL CONGRESS ON SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) AND
                       RELATED CONDITIONS IN NEW YORK CITY

NEW YORK, MAY 10, 2004 - La Jolla Pharmaceutical Company (Nasdaq: LJPC) today
announced that Company scientists will be giving four presentations on
previously released data on Riquent(R) (abetimus sodium), its drug candidate for
the treatment of lupus renal disease at the 7th International Congress on
Systemic Lupus Erythematosus (SLE) and Related Conditions which is being held on
May 10-13, 2004 in New York City.

More than 1,000 clinicians and scientists from around the world are expected to
attend the International Congress on SLE to discuss the latest research and
review the development of new treatments for 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, yet no new lupus drugs have
been approved in the United States in approximately 30 years. For additional
information on the 7th International Congress on Systemic Lupus Erythematosus
(SLE) and Related Conditions, please visit the website at http://lupus2004.org.

In conjunction with the International Congress, more than 100 lupus patient
advocacy organizations will host a press conference at noon today to observe
World Lupus Day. The press conference will feature presentations by individuals
with lupus, caregivers, clinicians, researchers, and lupus advocates who will
discuss the physical, economic and emotional impact of the disease on
individuals, families and society.

"There is a significant unmet medical need worldwide for improved therapies for
lupus patients," said Dr. Robert Lahita, M.D. Ph.D., Chairman, Department of
Medicine, Jersey City Medical Center and SLE Congress Chairman. "One of the
lupus community's key goals is the development of new and potentially safer
treatment alternatives. The International Congress on SLE is an opportunity to
bring physicians, scientists, patients, lupus advocacy organizations and
biotechnology companies together in support of this goal." Matthew Linnik,
Ph.D., Chief Scientific Officer and Executive Vice President of Research for La
Jolla Pharmaceutical Company, 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"

Lupus physicians who were clinical investigators in studies of patients treated
with Riquent will present three posters summarizing additional Riquent data:

      -     "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"

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. Latinos, African
Americans and Asians face an increased risk of serious renal disease associated
with lupus. Approximately 50% of lupus patients have renal disease, which can
lead to irreversible kidney damage, kidney failure and the need for dialysis.

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,
miscarriage 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.

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