Eighteen adult diabetic patients were treated with methandrostenolone in daily doses of 15 mg for 3 weeks. Serum triglyceride and cholesterol levels and lipoprotein lipase activity were determined before and after treatment. In patients with intense hypertriglyceridaemia, triglyceride concentration decreased and, with the exception of a single patient, lipoprotein lipase activity returned to normal. Cholesterol concentration did not change characteristically.