BACKGROUND: Insulin resistance in visceral obesity constitutes a risk factor for the development of atherosclerosis. The insulin resistance in obese type 2 diabetic patients can be improved by a decrease in the visceral fat and an increase in the skeletal muscle, which may influence the insulin sensitivity. Growth hormone (GH) accelerates lipolysis and promotes protein conservation. The effects of GH therapy, with diet restriction, on lipolysis and protein anabolism, were evaluated, which may change body composition, insulin resistance and atherosclerotic risk factors in obese type 2 diabetes mellitus. METHODS: Sixteen obese type 2 diabetic patients (31~56yrs), who had high glucose levels (glucose 12.8+/-1.7 mmol/L, HbA1c 10.2+/-2.1%), were treated with recombinant human GH (GH; 1 unit/d, 5 times/week), diet restriction (25 kcal/kg ideal body weight/day) and exercise (250 kcal/day) for 12 weeks. They underwent anthropometric measurement, bioelectrical impedance for total body fat and lean body mass, as well as computed tomography, for visceral and subcutaneous fat, at the umbilicus and muscle area at the mid-thigh levels. All subjects underwent the test for GH response to hypoglycemia. The insulin sensitivity index (ISI) was measured using insulin tolerance tests (ITT). RESULTS: 1. The visceral fat area (VFA)/thigh muscle area (TMA) ratio was more decreased in the GH-treated group than in the control group, but there was no change of body weight. 2. The ISI was significantly increased in only the GH-treated group, which was negatively correlated with the VFA/TMA ratio. The serum free fatty acid, fibrinogen and plasminogen activator inhibitor-1 were significantly decreased after the GH treatment. The serum glucose level and HbA1c remained unchanged during the GH therapy, but were significantly decreased after 3 months. 3. The total cholesterol and triglyceride levels were decreased in the GH treated group. 4. The insulin-like growth factor-I, fasting c-peptide and insulin level were all significantly increased after the GH treatment. CONCLUSION: This study suggested that in type 2 diabetic patients, with insulin resistance and uncontrolled blood sugar, GH treatment caused a decrease in the visceral fat and an increase in the muscle mass, which could result in the improvement of the ISI, atherosclerotic risk factors and dyslipidemia.