It is postulated that antioxidants reduce platelet activity by the stimulation of prostacyclin synthetase by scavenging synthesis-inhibiting peroxides. The experimental and clinical evidence supporting this theory is inconclusive. Clinical trials suggest that vitamin E reduced platelet aggregability. Nonexperimentally, a strong association has been observed between low serum selenium concentration and increased platelet aggregability. These findings suggest that antioxidants have an important role in the regulation of platelet function.