Therapeutic efficacy was studied in nine acromegalic patients. Eight were initially treated with supervoltage radiation therapy. Of these, four subsequently underwent surgery. Indices of "activity" correlated poorly with levels of somatotropin (STH). The other four had a satisfactory result manifested by a reduction in basal somatotropin level to normal, retention of anterior pituitary function, and absence of extrasellar extension. It is suggested that these patients have a small, or slow-growing adenoma, characterized by lower somatotropin levels and no extrasellar extension of hypopituitarism. Supervoltage radiation appeared to be best for this group. Reduction in somatotropin levels increased with time after radiation. Patients who would have been better managed with surgery had a large, or rapidly growing tumor and had clinical characteristics of hypopituitarism, hypothalamic extension, and visual field encroachment.