In vivo study of blood coagulation and fibrinolysis activities in non insulin dependent diabetes mellitus. The aim of the study was to investigate in vivo blood coagulation and fibrinolysis activities in a group of diabetic patients NIDDM with and without vascular complications. For this purpose we determined two sensitive indicators in vivo of blood coagulation and fibrinolytic activities such as fibrinopeptide A and B beta 15-42 respectively. Moreover, we computed the ratio between B beta 15-42 and fibrinopeptide A in order to investigate a possible imbalance in vivo between blood coagulation and fibrinolysis. Control groups were 15 healthy subjects and 28 non diabetic patients affected by atherosclerotic disease. Fibrinopeptide A and B beta values were significantly higher in the diabetic patients than controls but there was no difference between the former group and the atherosclerotic patients. Also, no correlation was found for FPA, B beta, B beta/FPAr and HbAlc, fructosamine and blood glucose levels. There was no difference in B beta, FPA and B beta/FPAr values for patients treated with insulin and for those treated with either hypoglycemic agents or diet. Our data indicate that in diabetic patients fibrinolysis activity is increased, but it cannot counterbalance thrombin activity which appears much more enhanced. Finally, the lack of correlation for FPA, B beta, B beta/FPAr and HbAlc, fructosamine and blood glucose suggests that blood coagulation and fibronolysis abnormalities are not related to the degree of blood glucose control.