Levels of lipolytic hormones (growth hormone, cortisol, and glucagon), insulin, and free fatty acids were measured in a patient with benign symmetric lipomatosis during a 5-hr glucose tolerance test, an insulin tolerance test, a 24-hr fast, and an epinephrine infusion. Although there was no abnormality in insulin dynamics or impairment in lipolytic hormone secretion, there was a failure of free fatty acid concentrations to rise to expected levels during fasting and after glucose. Insulin hypoglycemia and epinephrine infusion resulted in normal and excessive free fatty acid responses, respectively. This pattern of free fatty acid release is consistent with functional sympathetic denervation of adipose tissue. The lipomatous fat in benign symmetric lipomatosis is similar in distribution to the brown fat of human newborns and rodents that may hypertrophy after denervation. It is suggested that the lipomas in this disorder may represent such brown adipose tissue.