The aim of the study was to evaluate plasma concentration of fibrinogen, plasma activity of antithrombin III (AT-III) and plasma activity of plasminogen activator inhibitor (PAI-I) in insulin-dependent diabetic (IDDM) patients and the assessment of correlation between them and the parameters of glyco-metabolic control comprising glycemia and concentrations of fructosamine and glycated hemoglobin HbA1c. Eighteen IDDM patients (mean age 28.3 +/- 11.3 ys, mean duration of disease 12.2 +/- 5.3 ys) without over nephropathy and without macroangiopathy were investigated. Control group consisted of 8 healthy subjects. Plasma fibrinogen concentrations were similar in IDDM patients and in controls (3.54 +/- 0.45 g/l and 3.31 +/- 0.54 g/l respectively). Plasma activity of AT-III in diabetic patients (90.6 +/- 22.4%) was similar to that in healthy subjects (94.6 +/- 25.0%). Fibrinogen concentrations and AT-III activities showed no correlation with glycemia and concentrations of fructosamine and HbA1c. Plasma activity of PAI-I was significantly lower in diabetics than in controls (respectively 1.56 +/- 0.72 U/ml and 2.75 +/- 1.25 U/ml, p < 0.005). PAI-I activity correlated negatively with fasting blood glucose (p < 0.05) but did not correlate with concentrations of fructosamine or HbA1c. The results suggest that glycemic control in diabetic patients do not influence on concentrations of fibrinogen and activity of AT-III but diminished activity of PAI-I is related to hyperglycemia.