The induction of experimental nephrosis in diabetic rats resulted in a fall in hyperglycemia and glycosuria despite unchanged food intake. Nephrotic animals with or without diabetes showed a significant increase in the half disappearance time in serum of intravenously injected insulin I131. The extent of insulin sequestration in liver, kidney and muscle did not change uniformly with changes in insulin half disappearance time in serum. It is suggested, therefore, that the prolonged persistence of insulin in the serum of nephrotic and nephrectomized rats is due to diminished or absent degradation of the hormone by kidney tissue per se. These observations are consistent with, but do not necessarily explain, the low insulin re-quirement of some patients with the Kimmelstiel-Wilson syndrome.