Abstract An experimental model for the study of platelet-vessel wall interactions has been developed, based on perfusion of rat platelet-rich plasma (PRP) through isolated rat aortas. In the perfused PRP, platelet aggregation was inhibited and levels of 6 Keto PGF 1α and cAMP were elevated over the values found in non perfused PRP. When PPP or buffer were perfused through the isolated artery, elevations of 6 Keto PGF 1α levels in the perfusate were smaller (in perfused PPP) or of shorter duration (in both perfused PPP and buffer). The presence of platelets in the perfusion fluids thus enhanced the formation of Prostacyclin by the arterial wall. Levels of 6 Keto PGF 1α in PRP obtained from aspirin-treated animals and in PRP from normal animals, both perfused through normal aortas, were the same, and also levels of the above metabolite in normal PRP perfused through aortas of aspirin-treated animals did not differ from those found in non perfused PRP. It is concluded, from these data, that PRP does not stimulate PGI 2 formation in perfused aortas by providing cyclic endoperoxides. The experimental model developed allows the study of interactions between normal platelets and aortas from experimentally treated animals or viceversa.