Lever-pressing by squirrel monkeys was maintained under a continuous avoidance schedule in which each response postponed for 30 s the delivery of an electric shock to the tail. Dose-response curves were determined for chlorpromazine (0.03--0.3 mg/kg) and d-amphetamine (0.03--1.0 mg/kg) administered alone and administered concomitantly with 1.0 or 10 mg/kg of naloxone. The dose-response curves for chlorpromazine and d-amphetamine were similar to those previously reported for monkeys under other schedules of shock-maintained behavior: Chlorpromazine decreased responding in a dose-related manner while d-amphetamine increased responding at low doses and disrupted behavior at the highest dose. Naloxone did not modify the effects of chlorpromazine and d-amphetamine. These results suggest that interactions observed previously between naloxone and nonopiate drugs on behavior in pigeons and rodents are not general phenomena in all animal species.