Platelet volume, aggregation, and adenosine triphosphate release in cerebral thrombosis. We compared whole blood platelet aggregation, adenosine triphosphate release, platelet count, platelet crit (percentage volume of platelets), and mean platelet volume during the acute, subacute, and chronic periods of cerebral thrombosis in 22 patients with value in 29 controls. During the acute and subacute periods, platelet aggregation, platelet count, platelet crit, and mean platelet volume were significantly less in the patients than in the controls (p less than 0.05-0.01) while the adenosine triphosphate release rate per volume of platelets was significantly greater (p less than 0.05). During the acute period, infarct size showed a significant positive correlation with platelet aggregation (r = 0.59, p less than 0.01) and adenosine triphosphate release rate (r = 0.70, p less than 0.001) but a negative correlation with platelet count (r = -0.44, p less than 0.05). Our results suggest that platelet aggregation is reduced during the acute period due to the consumption of platelets during thrombogenesis but that the remaining individual platelets are hyperactive. Platelet consumption during the acute period increases with infarct size. During the chronic period, platelet crit and mean platelet volume were significantly less in the patients than in the controls (p less than 0.01) while the adenosine triphosphate release rate was significantly greater (p less than 0.01), suggesting sustained platelet consumption and chronically enhanced secretion of individual platelets. 