Adipocytes from 26-week-old Zucker rats (greater than 600 g) and controls of the same strain and age (greater than 400 g) served as models of insulin resistance and obesity. Adipocytes from fatty rats demonstrated insulin resistance of glucose metabolism and resistance to the antilipolytic effect of insulin which was not improved by fasting. Adipocytes from fatty rats were also resistant to the lipolytic action of norepinephrine. Control rats displayed insulin resistance of glucose metabolism and resistance to the antilipolytic effect of insulin. However, fasting for 6.5 days restored the antilipolytic action of insulin without affecting the insulin sensitivity of glucose metabolism. This dissociation of the responsiveness of insulin actions by fasting indicates that there may be at least two mechanisms of insulin resistance in the same cell.