The objectives of this study were to (a) determine whether the improvement in insulin action induced by short-term exercise training in patients with type 2 diabetes is due to an improvement in insulin sensitivity, in insulin responsiveness, or a combination of improved insulin sensitivity and responsiveness; and (b) determine whether short-term exercise training results in improved suppression of hepatic glucose production by insulin. Fourteen obese patients with type 2 diabetes, age 64±2 yr, underwent a two stage hyperinsulinemic euglycemic clamp procedure, first stage, 40 mU/m²/min insulin infusion, second stage 1000 mU/m²/min insulin infusion, together with a [3-³H]glucose infusion, before and after 7-days of exercise. The training consisted of 30 min of cycling and 30 min of treadmill walking at ~70% of maximal aerobic capacity daily for 7 days. The exercise program resulted in improvements in insulin action in the absence of weight loss. Glucose disposal rates during the euglycemic clamp were significantly increased at both hyperinsulinemic stages after training (40 mU: 1.84±0.32 to 2.67±0.37 mg/kg/min, P<0.0001; 1000 mU: 7.57±0.61 to 8.84±0.56 mg/kg/min, P=0.008). Hepatic glucose production, both in the basal state (3.17±0.43 vs. 2.54±0.26 mg/kg/min; P=0.05) and during the 40 mU clamp stage (1.15±0.41 vs. 0.46±0.20 mg/kg/min; P=0.03), was significantly reduced after training. One week of vigorous exercise training can induce significant improvements in insulin action in type 2 diabetes. These improvements include increased peripheral insulin sensitivity and responsiveness as well as enhanced suppression of hepatic glucose production.