Rats were trained to obtain food pellets in an 8-arm radial maze until a criterion of 89% efficiency, i.e., all arms entered within 9 arm entries, was reached in 5 consecutive sessions. Decreases in efficiency caused by phencyclidine (PCP; 4 to 9 mg/kg, IP, 15 min before testing) or ketamine (25 mg/kg, IP, 5 min) were attenuated when subjects were pretreated with clonidine (0.05 mg/kg, IP, 30 min). However, significant improvements in performance in the maze were not observed when clonidine (0.05 to 0.4 mg/kg, IP) was administered 15 min after PCP (9 mg/kg, IP, 45 min). Subsequent studies of righting reflex demonstrated an increased frequency and duration of anesthesia when clonidine (0.05 mg/kg, IP) was administered 15 minutes before PCP (12.5 to 50 mg/, IP) or ketamine (50 to 100 mg/kg, IP). When clonidine (0.05 mg/kg, IP) was administered 15 minutes before [3H]PCP (40 μCi/kg, IP), brain levels of tritium were reduced by 42 to 55%. The present findings do not support the suggestion that clonidine may be useful in the treatment of PCP intoxication. The data do indicate that pretreatment of surgical patients with clonidine may reduce the dose of ketamine required for anesthesia.