THE SYNDROME of inappropriate secretion of the antidiuretic hormone (ADH) was originally described by Schwartz and his co-workers1in two patients with bronchiogenic carcinoma. The most outstanding clinical findings were the signs and symptoms of water intoxication, and the outstanding laboratory finding was hyponatremia. Fuisz,2in an extensive review of hyponatremia, has outlined the following criteria for diagnosis of inappropriate ADH secretion: (1) hyponatremia, (2) renal sodium loss and hypertonic urine, (3) symptoms of water intoxication, (4) resistance to correction by hypertonic saline infusions, and (5) reversibility following water restriction. The syndrome has been described in a variety of disease states, many of them involving the central and peripheral nervous system. It has been seen with cerebral injury,3encephalitis,4poliomyelitis,4meningitis,5polyneuritis,6diffuse cerebral damage in infancy,7supratentorial8and infratentorial9brain tumors, following irradiation of an intrasellar tumor,10