Attempts were made to evaluate indirectly the ability of the pituitary gland to produce ACTH, in relation to increasing age, using the metyrapone test. Twelve aged subjects, average age 77 years, and 11 young control subjects were investigated. The effects of intravenous infusions of 5 g of metyrapone were examined. Plasma cortisol and plasma compound S were checked over a period from 8 a. m. to 8 p. m. Statistical analysis of the results revealed no significant difference between the reactions in the aged and the young. Side effects are discussed.