The principal product of arachidonic acid in the platelet is thromboxane A2 This compound is the most potent endogenous platelet agonist and vasoconstrictor known in man. Thromboxane A has been implicated in diverse human diseases in which platelet activation and vasospasm are known to occur. There has therefore been considerable interest in the development of therapeutic regimens designed to inhibit thromboxane biosynthesis. The studies described in this thesis investigated endogenous formation of thromboxane in human syndromes of platelet activation and examined the biochemical and functional effects of different approaches to inhibition of thromboxane production in health and disease.