Because we found previously that fructose feeding could alter lipolytic responses to isoproterenol and insulin in normal rats, we studied the effects of the same diet in neonatal, streptozotocin-diabetic rats. Twenty-seven 5-wk-old diabetic Sprague-Dawley rats were fed a diet containing 57% carbohydrate as either fructose, dextrose or starch for 6 wk. At the end of the nutritional period, plasma glucose and insulin concentrations in fed rats were similar in the three diabetic groups. Plasma triacylglycerol concentrations were higher in the fructose-fed group than in the other two groups (P < 0.05). Neither the maximal adipocyte lipolytic response (fructose = 1147 +/- 165%, starch = 1823 +/- 329% and dextrose = 1287 +/- 239% of basal values) nor the sensitivity to isoproterenol (ED50) was changed by the dietary carbohydrate exchange. The maximal antilipolytic action of insulin (starch = 68 +/- 10%, dextrose = 41 +/- 13%, fructose = 95 +/- 29% of stimulated lipolysis values) was comparable in the three diet groups. Thus, 6 wk of fructose feeding in diabetic rats increased plasma triacylglycerol concentrations, but had no detectable effect on plasma glucose or insulin concentrations, isoproterenol-induced lipolysis or the antilipolytic action of insulin.