Platelet function and prostaglandin activity were evaluated in nine patients with coronary artery disease undergoing percutaneous left anterior descending coronary artery angioplasty (PTCA) and compared to nine normal controls. Transcoronary measurements (arterial-coronary sinus) of platelet counts, mean platelet volume, platelet factor 4 (PF4), beta thromboglobulin, thromboxane (B2), and 6-keto-PGF 1 alpha were made. When compared to normal controls, the patients with coronary artery disease had higher circulating baseline levels of PF4 in the coronary sinus. There was no transcardiac production of any factor at baseline or immediately after infusion of nitroglycerin or performance of PTCA. These results suggest that PTCA does not grossly alter arachidonic acid metabolism or platelet activity.