Immobilization of adult male rats resulted in concomitant, significant releases of prolactin (PRL) and oxytocin (OT). Naloxone (0.2 mg/kg, i.p.) administration 30 min prior to initiation of restraint resulted in a significant diminution of the PRL response to stress. On the other hand, a significant augmentation of OT release was observed. These results demonstrate that concomitant releases of OT and PRL in response to a given physiologic stimulus (stress) can be dissociated and suggest that the hypothalamic events which are responsible for the release of these hormones during stress are different.