Understanding the sand rat's metabolic responses is necessary in order to employ the animal gainfully in the study of diabetes. Weanlings are most susceptible to the effect of diabetogenic diets. In the present experiment, weanling sand rats were fed diets at 3 levels of energy intake. The diets were based on pellets composed of different ratios of salt bush (Atriplex halimus) and a standard laboratory animal chow pellet. The results showed a significant correlation between the level of energy intake, percent body fat and signs of Type 2 diabetes. Animals with 28-30.6% body fat had blood glucose levels of 260 +/- 66 mg% and plasma insulin concentrations of greater than 558 mu u/ml, and those with 17.9-24.0% body fat had a blood glucose level of 107 +/- 19.8 mg% and a plasma insulin level of 222 +/- 35 mu u/ml. Animals with approximately 10% body fat, had a blood glucose level of 60 +/- 1.9 mg% and a plasma insulin concentration of 35 +/- 10 mu u/ml. The fattest animals had the highest percentage of glycosylated hemoglobin. The animals with the highest quantity of fat receiving high caloric intake had a lower lean body mass than those of similar weight exposed to a lower caloric intake. This result could be accounted for by assuming that the extreme hyperinsulinemia promoted fat production at the expense of lean body mass.