The effect of arginine infusion on blood sugar and plasma levels of growth hormone and glucagon has been studied in children with clinical diabetes mellitus and in obese children with normal carbohydrate tolerance. Basal levels of plasma GH are significantly lower in obese children than in diabetics and controls; in obese subjects the increment of GH is significantly lower than in diabetics and controls. Basal plasma glucagon levels are comparable in all three groups despite the high sugar levels in diabetic patients. After arginine infusion there is a significant rise in glucagon levels without significant differences between the three groups.