The function of platelets and erythrocytes and content of Willebrand's factor in the plasma from 45 patients with exercise-induced or spontaneous angina pectoris were examined before and after ergometrine, 0.1 mg. The patients with a negative ergometrine response showed a lower platelet sensitivity to all the aggregation inductors used in vitro, spontaneous platelet aggregation being absent. The function of erythrocytes and plasma levels of Willebrand's factor remained unchanged. The patients with a significant ischemic response to ergometrine exhibited platelet activation attended by the release of granule contents and formation of blood circulating platelet microaggregates. Concurrently, there was a decrease in erythrocyte deformability, as well as spontaneous blood red cell aggregation, the plasma levels of Willebrand's factor were increased 1.5-2-fold.