Pentobarbital in a dose of 3.5 mg/100 g b.w. did not suppress the high basal a.m. levels of plasma ACTH in adrenalectomized male rats. In both intact and adrenalectomized rats prior administration of the drug slightly depressed the rise in plasma ACTH induced by 2.5 min of ether inhalation, but this depression is of questionable statistical significance.