Alcoholism has been shown to predispose to cerebrovascular thrombosis in normotensive males under the age of 50. To elucidate this phenomenon platelet aggregation and fibrinolytic activity were studied in 29 alcoholic males under 50 years of age who showed no evidence of acute cerebrovascular disease. Age matched healthy nonalcoholic volunteers made up the control population. Platelet aggregation did not differ significantly (P greater than 0.05) in the two groups. Fibrinolytic activity was significantly reduced in the alcoholics as compared to the controls (P = 0.005). The data suggest that the alcoholics have an increased thrombotic tendency. This may cause alcoholics to be at a greater risk of suffering stroke at an early age.