Responses of squirrel monkeys adjusted the intensity of a continuous electric shock under 2 different schedules. In 1 schedule, responses decreased a shock intensity which otherwise was increased at a fixed rate (escape). In the other schedule, responses produced food pellets but also increased a shock intensity which otherwise decreased at a fixed rate (punishment). When animals were 1st studied under the escape schedule, d-amphetamine, a CNS stimulants, increased responding. When animals had an intervening experience under the punishment schedule with no drugs administered, or when the drug was given but shock increments were temporarily eliminated during those drug sessions, d-amphetamine still increased subsequent escape responding. When animals under the punishment schedule were given d-amphetamine and shock increments occurred as usual during the drug session, the drug no longer increased either punished or subsequent escape responding. The effects of d-amphetamine on escape responding were completely different depending on the individual''s prior drug experience.