It has been reported that delta-sleep-inducing peptide (DSIP) can affect several activities other than sleep, including reduction of stress. We studied the effects of this nonapeptide on corticotropin releasing factor (CRF)-stimulated release of corticosterone in rats treated with chlorpromazine-morphine-pentobarbital. Significant reduction of corticosterone levels were observed after intravenous injection of 5–30 µg/kg DSIP. No effect of DSIP was found on the corticosterone release elicited by injection of adrenocorticotropic hormone. The results suggest that DSIP attenuates the effects of CRF at the level of the pituitary.