Fifty-eight acromegalic patients were included in a multicenter prospective study of increasing doses β00–1500 μg) of SMS 201–995 (octreotide, Sandostatin) administered 3 times daily, sc, during 6 months to determine its effects on signs and symptoms of GH hypersecretion. Subsequently, 34 of the patients were maintained for 12–26 months on the minimal efficacious dose, determined from the previous dose-response study. Some adverse effects were frequently encountered, mostly at the initiation of treatment, and disappeared with time. Asymptomatic gallstones occurred in 5 patients. Minimal changes in carbohydrate tolerance, consisting of a rise in blood glucose and a transient decrease in plasma insulin level after meals, were noted. GH normalized in 22% of the patients, improved in 56%, and remained unchanged in 22% regardless of the dose. The optimal daily dose was 300 μg in 50% of the patients and 1500 μg in 20%. Pituitary tumor size reduction occurred in 47% of the patients harboring large tumors or tumor remnants. No additional improvement or escape from being controlled occurred with time. These data indicate that SMS 201–995 is an effective treatment for refractory acromegaly and for some de novo patients for whom surgical therapy is not advisable. © 1990 by The Endocrine Society.