A multicompartment chamber was used to study the investigatory behavior of mice in a novel environment. Restraint stress, subcutaneous morphine (1.75 mg/kg), and ICV corticotropin-releasing factor (CRF; 75 ng) each produced a decreased mean time per contact with novel stimuli. The effect of all three treatments was antagonized by a dose of naloxone that by itself had no significant behavioral effects (0.7-0.75 mg/kg). Naloxone alone at a higher dose (1.25 mg/kg), increased the mean time per contact with the stimuli. These results confirm previous reports of the effects of opiates and stress on this behavior in rats. The similarity of the effects of CRF and stress on the behavioral response to this chamber supports the possibility that CRF may act in the central nervous system to mediate certain behavioral responses in stress.