Food-maintained responding by four squirrel monkeys (Saimiri sciureus) was suppressed by the presentation of electric shock (punishment). Two of these monkeys were experimentally naive and two had a history of responding maintained by both shock-postponement and shock-presentation schedules. In accord with earlier studies, d-amphetamine did not increase punished responding by naive monkeys. However, it did increase punished responding in the others. Subsequently, d-amphetamine also increased punished responding by the initially naive monkeys after they were trained under a shock-postponement schedule. Even though not evident in current behavior, an organism's prior experience can influence the behavioral effects of drugs.