Two-month hyperphagia after injury inflicted to the ventromedial hypothalamus in rats led to the development of marked obesity in an essential increase of the content of immunoreactive insulin, glucagon, and C-peptide in the blood. Increase of excessive body weight was attended by gradual diminution of the organisms sensitivity to exogenous insulin given in a dose of 0.03 U/100 g and maintenance of normal sensitivity to 0.1 U/100 g of exogenous insulin. It is most likely, therefore, that despite the increased function of the pancreatic islets and hyperinsulinemia, glucose tolerance decreased significantly due to diminished sensitivity of the peripheral tissues to insulin.