Administration of estradiol-17β for 7 days to the adult male rat results in adrenal hyperplasia, decreased serum corticosterone along with elevation in serum ACTH and inhibition of adrenal 5-ene-3β-hydroxysteroid dehydrogenase activity (5-ene-3β-HSD). Treatment with α2u-globulin for following 14 days of estrogen-treated rats reversed the effects of estrogen while in normal rats α2u-globulin treatment increased adrenal 5-ene-3β-HSD activity and serum corticosterone level while causing a fall in serum ACTH. It is concluded that α2u-globulin may play a role in ACTH secretion by inducing corticosterone synthesis. © 1988.