Abstract Earlier reports have indicated, that the platelet sensitivity to prostacyclin (PGI 2) is decreased in patients with coronary heart disease and that the onset of a spontaneous anginal attack is associated with a further decrease in platelet sensitivity to PGI 2. We studied platelet function before and after bicycle exercise testing in 23 patients with angina pectoris and in 11 healthy males. We could not demonstrate any difference in platelet sensitivity to PGI 2 between patients eats with angina pectoris and the controls neither before nor after exercise testing. The platelet sensitivity to PGI 2 decreased significantly after exercise, both in patients and in controls, but the decrease was not related to the development of myocardial ischemia. Our results could be interpreted in terms of different pathophysiological roles of platelets in spontaneous and in exercise-induced myocardial ischemia.