The effect of glyburide (glibenclamide) treatment on the muscle superoxide dismutase (SOD) activity of diabetic rats has been studied. 2. Four weeks of treatment with glyburide (5 mg/kg, orally) increased muscle SOD activity and decreased blood glucose levels. 3. The results of this study demonstrate that the sulfonylurea, glyburide, is capable of exerting direct insulin-like effects on muscle SOD activity in vivo.