37 type 2 diabetic patients with no clinical evidence of retinopathy or vascular disease were studied at diagnosis and following control of hyperglycaemia for evidence of abnormalities of coagulation, fibrinolysis and platelet behaviour. 38% showed hyperactive platelets, demonstrating either in vitro hyperaggregability, circulating platelet aggregates, or raised plasma beta-thromboglobulin levels. 36% showed abnormally raised factor VIII coagulant activity (FVIIIc) levels, though this was mainly in female patients. The mean level of FVIIIc decreased with treatment. Anti-thrombin III (AT-III) levels were decreased, and 33% of the patients had levels < 80%. In this group AT-III increased following treatment. No abnormalities of fibrinolysis were demonstrated. These findings support the concept that diabetes can be associated with a hypercoagulable state, which is not necessarily dependent on the presence of overt vascular disease, or correlated with the degree of chronic hyperglycaemia (HbA_1c levels).