This review focuses upon an animal model of relapse. The basic model is to establish that a drug is functioning as a reinforcer. Drug is then replaced with vehicle, and responding is allowed to extinguish. Exteroceptive or interoceptive stimuli are then presented to determine whether behavior that was previously reinforced by drug would be reinstated. Experimental attention has been directed toward using interoceptive stimuli (e.g., priming injections of the self-administered drug, other drugs of abuse or potential treatment drugs) to reinstate extinguished behavior. Drugs that function as reinforcers reinstate responding (relapse), although there have been few reports of reinstatement with drugs that are not reinforcing. Reinstatement usually occurs in a dose-dependent manner with a priming injection of a drug from the same pharmacological class. Restricted feeding and stress enhance relapse in cocaine-trained rats. Relapse occurs over several days or weeks of abstinence. This model is useful for the study of drug abuse treatment by identifying methods of behaviorally extinguishing or pharmacologically blocking relapse.