Rats adrenalectomized 4-6 d before a 15-min swimming test showed levels of immobility indistinguishable from controls. Retested 24 h later, adrenalectomized rats showed significantly reduced (28%) immobility compared with controls (70%) or hypophysectomized rats (60%), but not hypophysectomized-adrenalectomized rats (41%). The effect of adrenalectomy was reversed by the administration (within 1 h of initial test, but not subsequently) of dexamethasone (6-20 micrograms; 65% immobility) and corticosterone (6 mg; 74%), but not by the mineralocorticoid deoxycorticosterone (6 mg; 33%). [D-Ala2,Met5]enkephalinamide (5-50 micrograms) also restored immobility (66%). We postulate that hormones from both adrenal medulla and cortex are involved in the retention of information post-stress, and that these hormones act directly on the CNS rather than via the pituitary, since the response to adrenalectomy is not dependent on the presence of the pituitary gland.