Platelet functions were investigated in sixteen old (78-94 years) and eight young (25-35 years) subjects. Whole blood platelet aggregation induced by collagen was higher in the elderly. Similarly, aggregation of platelet rich plasma and plasma-free platelets induced by various agents was increased but the collagen-induced release of ATP was reduced. In agreement with the enhanced platelet aggregability, the increase of thromboxane formation (under thrombin stimulation) was also noted in platelets from elderly people. To further assess platelet and vascular function in vivo, we measured the excretion of urinary TXB2, 2,3-dinor TXB2, 6-keto-PGF1 alpha and 2,3-dinor-6-keto-PGF1 alpha. The four metabolites were all increased in the elder population. In addition, a significant reduction of platelet vitamin E was observed in the elderly people, although the plasma content was normal. These results indicate numerous modifications of platelet behaviour with aging. They include the increased platelet susceptibility to aggregation, and the depletion of ATP granule content, which could reflect an activation in vivo in agreement with the enhanced urinary excretion of thromboxane and prostacyclin metabolites. We hypothesize that platelet hyperactivity associated with the enhanced oxygenated metabolism of arachidonic acid could be linked to vitamin E depletion. These changes may reveal a prethrombotic state in the elderly population.