The effect of vitamin E administration on platelet function was evaluated in a group of normal, healthy volunteers. Platelet aggregation induced by collagen, ADP and epinephrine and platelet adhesion to collagen were measured at weekly intervals in 20 men and 27 women divided into 3 experimental groups of 12 individuals each and one control group of 5 men and 6 women. One experimental group was on a 6-week regimen of vitamin E in increasing dosages (400 I. U.--1,200 I. U.), the second group received aspirin, 300 mg every other day, and the third group was on a combination of vitamin E and aspirin. In the control group, platelet function was measured at weekly intervals. In women, vitamin E by itself produced a small but significant reduction of collagen-induced platelet aggregation. A similar trend was seen in men. However, the reduction never reached statistical significance. Adhesiveness to collagen was not affected by aspirin ingestion but showed a highly significant reduction in vitamin E and vitamin E + aspirin treated individuals. These results suggest that vitamin E administration could have a beneficial effect in patients suffering from arterial thromboembolic diseases.