The fibrinolytic system was investigated in 115 patients with maturity-onset diabetes mellitus in good metabolic control and without thromboembolic manifestations. The patients were divided into 7 groups according to the hypoglycemic therapy: diet alone, tolbutamide, glibenclamide, phenformin, combination of the last two drugs, insulin, combination of insulin and phenformin. Our results indicate that in maturity-onset diabetes both fibrinolytic activity and inhibitors of fibrinolysis are increased. The enhanced fibrinolytic activity was not affected by different hypoglycemic drugs, whereas the main antiplasmins showed wide variations in the different treatment groups. In particular, a significant reduction of alpha 2M was observed in patients on glibenclamide therapy. In conclusion, our study showed that the high fibrinolytic state seems to be a constant element in diabetes, and that the different behaviors of the fibrinolytic system, reported by various authors in patients taking different hypoglycemic drugs, could be explained by the wide range of plasmin inhibitor levels observed in these conditions.