Pituitary trophic hormone function was evaluated in two groups of acromegalic patients. The first consisted of 12 patients who were studied before undergoing conventional x-ray therapy. Of these 12, five were found to have trophic hormone deficiencies. After therapy two regained gonadotrophic function while three developed new deficits. In the second group of 16 patients, who were studied only after radiation treatment, seven had loss of one or more trophic hormones. As a combined group, 15 of 28 acromegalics studied (54%) had deficits. Hypogonadotrophism was most frequent, followed next by loss of thyrotrophin and then corticotrophin. In general, hypopituitarism could not be related to tumor size, duration of disease, or therapy. This relatively high incidence of pituitary insufficiency in acromegaly suggests that when evaluating and treating acromegalics careful attention should be given to this complication.