Thromboxane synthase (TS) catalyzes the conversion of the prostaglandin endoperoxide into thromboxane A2 (TxA2), a potent vasoconstrictor and inducer of platelet aggregation. In concert with prostacyclin TxA2 plays a pivotal role in the maintenance of hemostasis. Deficiency of platelet TS activity has been shown to result in bleeding disorders. The potent effect of TxA2 on platelet function and vascular activity suggests a possible involvement of TS in normal and pathophysiological conditions such as cardiovascular disease. To aid in establishing the correlation of TS to disease states, we localized the human TS gene (TBXAS1) to chromosome 7q34-q35 using dual-color fluorescence in situ hybridization.