OBJECTIVE: To measure plasma endothelin 1 (ET-1) levels in uncomplicated non-insulin-dependent diabetes mellitus (NIDDM) and investigate whether ET levels may be related to angiopathy, blood pressure, metabolic control, or duration of illness. RESEARCH DESIGN AND METHODS: Plasma levels of ET-1 were measured in 44 NIDDM patients, of whom 24 had uncomplicated diabetes, 20 had angiopathy, and 10 had hypertension. In 21 patients, the duration of illness was > 10 years, and in 23 the duration of illness was <10 years. Serum creatinine levels, microalbuminuria, and HbA1c were determined simultaneously. Thirty normotensive healthy (nondiabetic) individuals (20 men and 10 women) served as control subjects. RESULTS: No significant statistical differences in plasma ET-1 levels were found among all diabetic patients, diabetic patients with and without angiopathy, diabetic patients with different durations of diabetes, and normal subjects. No significant correlation of plasma ET-1 with blood pressure, age, serum creatinine level, duration of diabetes, HbA1c, or diabetic complications was found. CONCLUSIONS: Plasma ET-1 levels are similar in patients with NIDDM and healthy subjects and do not seem to act as a marker of diabetic complications.