A correlation between increased platelet adhesiveness and aggregation and the development of angiopathy in diabetes mellitus can be made. Thromboxane produced by platelets represents a potent platelet aggregation factor. We studied the platelet TXB2 production during blood coagulation in carefully selected patients with type II diabetes mellitus in good metabolic control and the results were correlated with the presence or absence of microangiopathy, fasting blood glucose levels, type of therapy, age, duration of diabetes and the most important hematochemical parameters. No statistically significant differences were found between serum TXB2 concentrations in diabetic patients and control subjects, in diabetics with or without microangiopathy and in diabetics on insulin therapy or on oral hypoglycemic agents. We did not observe any correlation between TXB2 production and age, duration of diabetes, sex, basal blood glucose levels, total and HDL-cholesterol, triglycerides, blood creatinine and blood electrolytes. The thromboxane production may be a not important factor for determining the increased platelet aggregation which is at the origin of the angiopathy in diabetes mellitus.