The functional activity of platelets was examined in patients with coronary heart disease and healthy individuals during cold test (CT). Patients prone to vasospastic responses to CT exhibited platelet activation along with beta-thromboglobulin release and formation of spontaneous platelet aggregates. Comparison of functional changes in platelet functional activity which occurred during cold test and intravenous ergometrine test suggest that the response to CT may be substantially higher if platelet aggregability is concurrently determined. The unidirectional changes in platelet aggregability during cold and ergometrine tests in patients with signs of dynamic coronary occlusion may indicate a relation of platelets with coronary vasoconstriction.