Squirrel monkeys self-administered cocaine by pressing a lever while under a variable-interval schedule of reinforcement. At the same time, they terminated the availability of self-administered cocaine by pressing a second lever while under a fixed-interval schedule of reinforcement. The maintenance of behavior by schedule drug injections and by termination of scheduled drug injections, usually considered to be processes associated with different classes of drugs, can occur simultaneously when behavior is controlled by different contingencies associated with a single drug.