There are several situations in which medical therapy of hyperinsulinism induced by islet cell tumors or hyperplasia is necessary and at present we have at our disposal several drugs which are capable of reducing endogenous hyperinsulinism. They are: -Streptozotocin, which represents today the most useful therapeutic agent for beta cell carcinoma therapy; -Diazoxide, which represents the drug of first choice for the treatment of most hypoglycemic syndromes caused by islet cell adenoma or hyperplasia; -Propranolol, Chlorpromazine, Diphenylhydantoin, which may be regarded as a useful alternative to diazoxide, although they are capable of giving rather inconstant results. These drugs may today effectively substitute for corticosteroids and glucagon in the medical treatment of almost every chronic hyperinsulinemic hypoglycemic syndrome, including malignant beta cell carcinoma.