Signs and symptoms of Cushing's syndrome developed rapidly after total gastrectomy in a 37-yr-old man with a metastatic gastrin-secreting islet cell carcinoma. Argyrophilic tumor cells in a lymph node removed during operation immunostained for gastrin and ACTH. Treatment for more than 6 months with the somatostatin analog SMS 201-995 (300 micrograms/day) greatly reduced serum gastrin levels and normalized plasma ACTH and cortisol levels and urinary cortisol excretion, and the signs and symptoms of Cushing's syndrome disappeared. The size of the primary tumor in the head of the pancreas, which had grown rapidly before SMS 201-995 therapy, stabilized after 6 months of treatment with the analog. We conclude that SMS 201-995 can reduce ACTH as well as gastrin secretion from islet cell carcinomas as well as control tumor growth.