Abstract Although the glucose-lowering properties of metformin are well-established, its effects on glucose metabolism in skeletal muscle have not been clearly defined. We tested the effects of metformin in young adult male Sprague-Dawley rats, which have a documented reduced response to insulin in skeletal muscle. Rats were treated with metformin for 20 days (320 mg/kg/day) in the drinking water. During this period, metformin completely prevented the increase in food intake and decreased adiposity by 30%. Metformin also reduced insulin secretion by 37% following an intra-peritoneal injection of glucose. Finally, metformin enhanced transport of [ 3H]-2-deoxyglucose in isolated strips of soleus muscle. Metformin substantially increased insulin-stimulated transport, while having no effect on basal transport. In control rats, a maximal concentration of insulin stimulated transport 77% above basal. In metformin-treated rats, insulin stimulated transport 206% above basal. We conclude that in the Sprague-Dawley rat model, metformin causes a significant increase in insulin-responsiveness.