Microalbuminuria in diabetic patients is associated with an increased cardiovascular risk which is not completely explained by an excess of conventional cardiovascular risk factors. A depression of physiologic inhibitors of blood coagulation could contribute to a thrombophilic state and to cardiovascular complications: data on protein C in diabetic patients are controversial, and no information exists about protein C activity in non-insulin-dependent diabetic patients or its relation to the microalbuminuric state. The aim of this study was to assess protein C activity in non-insulin-dependent diabetic patients with and without microalbuminuria. Protein C activity was determined (Protein C Reagent, Boehringer Mannheim, Germany) in 29 non-insulin-dependent diabetic patients with microalbuminuria (group A, > 20 micrograms/min), 33 non-insulin-dependent diabetic patients with normoalbuminuria (group B), and in 36 non-diabetic healthy blood donors as a control group (group C). The groups were matched for sex, and no difference in age, body mass index, blood pressure, glycated haemoglobin or known duration of diabetes was observed between groups A and B. Protein C activity was similar in the three groups (mean +/- SD): group A, 106.9% +/- 25.2%; group B, 109.3% +/- 27.6%; group C, 103.1% +/- 18.9%; F value 0.58, NS. Protein C activity did not correlate significantly with body mass index, glycated haemoglobin, known duration of diabetes, age or albumin excretion rate in any of the groups or in the diabetic patients as a whole. No significant difference in protein C activity was observed in patients taking other therapy (diet, oral agents, insulin).(ABSTRACT TRUNCATED AT 250 WORDS)