Antiplatelet drugs as exemplified by aspirin are used frequently to prevent stroke. Aspirin inhibits the formation of both the potent platelet aggregator, thromboxane A2 and the potent anti-aggregator, prostacyclin. Another approach to the inhibition of platelet aggregation might involve selective suppression of thromboxane formation. We report our experience in swine with UK-38,485, a drug which selectively inhibits thromboxane formation. The rationale and potential uses of UK-38,485 in the in vivo prevention of platelet aggregation and for the therapy of cerebrovascular disease are discussed.