LA JOLLA PHARMACEUTICAL COMPANY TO PRESENT AT
PACIFIC GROWTH AND NEEDHAM & COMPANY
INVESTOR CONFERENCES

SAN DIEGO, June 7, 2006 — La Jolla Pharmaceutical Company (Nasdaq: LJPC) today announced that Deirdre Y. Gillespie, M.D., President and Chief Executive Officer of La Jolla Pharmaceutical Company, will present at the Pacific Growth Equities Life Sciences Growth Conference on Monday, June 12, 2006 at 10:30 a.m. Pacific Time / 1:30 p.m. Eastern Time. The conference will be held at The InterContinental Mark Hopkins Hotel in San Francisco.

Dr. Gillespie will also be presenting at Needham & Company’s 5^th Annual Biotechnology and Medical Technology Conference on Thursday, June 15, 2006 at 8:00 a.m. Pacific Time / 11:00 a.m. Eastern Time. The conference will be held at The New York Palace Hotel in New York City. A live audio webcast of this presentation will be available and archived through the Company’s Web site: http://www.ljpc.com.

La Jolla Pharmaceutical Company is a biotechnology company developing therapeutics for antibody-mediated autoimmune diseases and inflammation afflicting several million people around the world. The Company is developing Riquent® for the treatment of lupus kidney disease, a leading cause of sickness and death in patients with lupus. The Company is also 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 and during the presentations involve and will 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. The results from our clinical trials of Riquent, our drug candidate for the treatment of systemic lupus erythematosus (lupus), and any other drug candidate that we may develop, 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 obtain marketing approval. There can be no assurance, however, that we will have the necessary resources to complete any current or future trials or that any such trials will be sufficient to obtain marketing approval. 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 with respect to its secondary endpoint, time to treatment with high-dose corticosteroids or cyclophosphamide. 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 SSAO inhibitor program is at a very early stage of development and involves comparable risks. We depend on patents and other proprietary rights, and our ability to develop and sell our products in the future may be adversely affected by the intellectual property rights of third parties. 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 additional risks described in our Annual Report on Form 10-K for the year ended December 31, 2005, and in other reports and registration statements that we file with the Securities and Exchange Commission from time to time.

###