Hypercoagulability may increase the risk of cardiovascular disease (CVD) in diabetic patients with albuminuria. Plasma thrombin-anti-thrombin III complex (TAT) levels, representing a functional state of clotting system, were studied in one hundred and fifteen non-insulin-dependent diabetic (NIDDM) patients. The patients were divided into three groups according to the urine albumin index (UAI: mg/g Cr): Group A; UAI < 30, Group B; 30 < UAI < 300, Group C; UAI > 300. The effect of albuminuria on plasma TAT levels was significant (p < 0.02). Ethyl icosapentatenoate (EPA: 1800 mg/day) for 4 weeks significantly (p < 0.0005) decreased plasma TAT levels. These data indicate that the degree of diabetic albuminuria is related to plasma TAT levels in NIDDM patients and that treatment with EPA may reduce TAT levels and possibly therefore the rate of development of CVD in patients with NIDDM.