Ca++ level in the platelets of patients with different forms of CHD (angina pectoris of new onset, including the spastic form, acute myocardial infarction) and of subjects without signs of CHD or coronary atherosclerosis was measured basally and after stimulation with ADP, platelet activation factor and serotonin. Simultaneously platelet aggregation induced by the same stimuli was studied. Basal platelet Ca++ did not differ significantly between the groups. Stimulation by ADP and serotonin increased Ca++ concentration, the change being greatest in patients with spastic angina pectoris. Augmentation of free platelet Ca++ in patients with acute myocardial infarction did not differ from that in subjects without CHD and coronary atherosclerosis, and in some cases it was even less pronounced. Free Ca++ level showed good correlation with platelet aggregation. It is suggested that the differences revealed are due to changes in the sensitivity of platelet receptors to the inductors used.