SC-58635 is a novel compound that selectively inhibits the inducible form of the enzyme cyclooxygenase (prostaglandin G/H synthase). SC-58635 is being developed by G.D. Searle & Co. as an oral antiinflammatory agent for the treatment of rheumatoid and osteoarthristis, and for the relief of pain of musculoskeletal and soft-tissue origin. The present study, partly supported by G.D.Searle & Co., is a double- blind, randomized, comparator and placebo controlled, parallel group, single dose study. A group of 35 healthy subjects who are 18-55 years of age will receive a single dose of either 100, 400 or 800 mg SC-58635, ibuprofen 800 mg or placebo. The primary objectives of this study are to: 1. determine the effect of SC-58635 on platelet aggregation to collagen, arachidonate and U46619 (Tx agonist) in healthy subjects; and 2. correlate the effects on collagen-, arachidonate and U46619-induced platelet aggregation with plasma concentrations of SC-58635.