Two groups of eight rats were trained to obtain food pellets in an 8-arm radial maze. Stable performance was assumed to be present when a criterion of 89% efficiency, i.e., all arms entered within 9 arm entries, was reached in 5 consecutive sessions. The effects of phencyclidine (PCP) and N-allyl-N-normetazocine (SKF-10,047) were then evaluated in Group 1. The interaction between verapamil and PCP was examined in Group II. Both PCP (6 mg/kg, IP, 15 min before testing) and SKF-10,047 (30 mg/kg, IP, 30 min) decreased efficiency but only PCP caused a concurrent increase in rate of arm entry. Significant effects of PCP on rate and efficiency lasted for greater than 6 hours and less than 40 minutes, respectively. Verapamil (20 mg/kg, IP, 30 minutes) was found to selectively potentiate the effect of PCP on efficiency. This finding does not support the suggestion that verapamil may be useful in the treatment of PCP intoxication. It is concluded that the radial maze may provide an interesting method for the study of PCP and other psychoactive drugs.