Prostacyclin is a potent but unstable vasodilator, and inhibitor of platelet aggregation, which is produced by blood vessel walls. Platelet aggregability may be constantly conditioned in vivo by local or circulating prostacyclin. Prostacyclin is important in the maintenance of vascular homeostasis and may be implicated in certain disease states. The use of prostacyclin in antithrombotic therapy appears logical, considering its action in increasing platelet cyclic AMP and reducing aggregation; its potential in antithrombotic therapy is presently being explored.