We studied 115 patients with uncomplicated maturity-onset diabetes mellitus, 55 males and 60 females; 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). All patients were tested for a prethrombotic state by the simultaneous determination of the following parameters: ADP-induced platelet aggregation, Factor VIII as antigen and procoagulant activity and the plasma levels of fibrinogen and antithrobin III. Our results show that these parameters were markedly altered in diabetic patients when compared to apparently normal subjects of the same age; on the contrary, differences between groups of diabetic patients were very slight and hardly ever statistically significant. These results suggest that the prethrombotic alterations of hemostatic system are very similar in all groups of diabetic patients; this is true also for patients submitted to diet alone, i.e. with slight and usually recent-onset diabetes mellitus. In conclusion, our study suggests the opportunity, at least from the theoretical point of view, of systematic antiaggregant and/or anticoagulant treatment(s) in maturity-onset diabetes mellitus, whose severe and precocious prethrombotic alterations seem to be independent of the hypoglycemic treatment applied.