The limited studies on chondrichthyean islet function are discussed and evaluated. The only certain effect is that of insulin-induced hypoglycemia in all species studied. Bovine and chondrichthyean insulin preparations both have pronounced effects. The evidence also indicates that glucagon is hyperglycemic in some species, but the source of the mobilized glucose is unknown. Blood glucose levels in the Chondrichthyes show wide variations, even within a species, and are apparently not closely regulated. To the present time the effects of pancreatic hormones on carbohydrate metabolism have been investigated, but other possible effects of these hormones on intermediary metabolism (e.g., protein and lipid) have not been studied. The sparse information on the immunology of chondrichthyean insulins is also discussed.