Exhibit 99.1

                  LA JOLLA PHARMACEUTICAL AUTOIMMUNE THROMBOSIS
            DISEASE TARGET HIGHLIGHTED IN TWO PEER-REVIEWED JOURNALS

SAN DIEGO, MAY 13, 2004 - La Jolla Pharmaceutical Company (Nasdaq: LJPC) today
announced that recent findings concerning antibody-mediated thrombosis, also
known as the Antiphospholipid Syndrome (APS), were published in the Proceedings
of the National Academy of Sciences and Clinica Chimica Acta. Antibody-mediated
thrombosis is an autoimmune disease that can cause stroke, heart attack, deep
vein thrombosis and other thrombotic events, and is the target of the Company's
early clinical drug candidate LJP 1082. LJP 1082 is the first drug candidate
specifically designed to target the underlying cause of antibody-mediated
thrombosis.

"Antibody-mediated thrombosis is an autoimmune condition first described in the
medical literature about 20 years ago, and it is believed to affect an estimated
one to two million people in the United States and Europe," said Steven Engle,
Chairman and CEO of La Jolla Pharmaceutical Company. "We are pleased to be able
to share the insights we have gained from our research with the medical
community through these widely read journals. We believe these data confirm the
importance of developing a drug candidate to target disease-causing antibodies
in antibody-mediated thrombosis."

BETA 2-GLYCOPROTEIN I, AN IMPORTANT REGULATOR OF BLOOD CLOTS

Company scientists and colleagues from St. George Hospital in Australia
published an article in the Proceedings of the National Academy of Sciences (T.
Shi, et al., 101: 3939-3944) entitled "Beta 2-Glycoprotein I Binds Factor XI and
Inhibits Its Activation by Thrombin and Factor XIIA: Loss of Inhibition by
Clipped Beta 2-Glycoprotein I." Beta 2-glycoprotein I is a blood protein
involved in coagulation and is a target of the antibodies involved in APS. The
paper identified an important role for beta 2-glycoprotein I in the regulation
of blood coagulation. The results showed that beta 2-glycoprotein I can inhibit
blood clotting by binding to coagulation Factor XI and preventing Factor XI from
being activated.

COMMONLY USED ASSAYS DETECT DOMAIN 1 OF BETA 2-GLYCOPROTEIN I

Company scientists also published an article in Clinica Chimica Acta (G. Michael
Iverson, et al., 343: 37-44) entitled "Advances in Understanding What We Measure
When Detecting Anti-Cardiolipin Autoantibodies." The authors of this paper used
commercial assays to demonstrate that the antibodies to cardiolipin and beta
2-glycoprotein I in patients with APS are highly specific for domain 1 of beta
2-glycoprotein I. In this study, 100 patient serum samples showed that antibody
reactivity in both assays was depleted by pre-incubating the sera with
recombinant domain 1 of beta 2-glycoprotein I.

ANTIBODY-MEDIATED THROMBOSIS

Antibody-mediated thrombosis is an autoimmune disease characterized by the
formation of blood clots that can lead to stroke, heart attack, deep vein
thrombosis and recurrent miscarriage. This disease, also known as
Antiphospholipid Syndrome, affects an estimated one to two million people in the
United States and Europe. Patients often experience their first thrombotic event
in their 20s or 30s, and studies indicate they have twice the probability of a
recurrence. Current treatments include anticoagulants, the long-term use of
which can lead to side effects including life-threatening bleeding events.

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, that
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

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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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