The effect of non-contingent priming injections of heroin on drug-reinforced behavior following long-term extinction was examined. Male rats were trained to lever press for 100µg/kg/infusion of intravenous heroin during four 6h sessions per day. The drug-reinforced behavior was extinguished by daily reductions in dose followed by at least 12 sessions of saline self-administration. A single non-contingent priming injection of heroin (100µg/kg, i.v.) resulted in the reinstatement of the drug-reinforced behavior, even though extinction conditions remained. The results indicate that the drug-induced reinstatement of previously extinguished drug-reinforced behavior is possible even after long periods of extinction. The implications of the present findings for the treatment of relapse to drug abuse in humans are discussed.