The purpose of the present study was to compare the reinforcing efficacy of 3,4-methylenedioxymethamphetamine (MDMA, ‘ecstasy’) to cocaine. Rhesus monkeys (n=4) responded under a within-session, exponentially increasing, progressive-ratio (PR) schedule of cocaine reinforcement. Breaking point (BP) for the PR schedule was defined as the final response requirement completed before 2h had elapsed without an injection delivered. Saline and doses of cocaine (0.003–0.3mg/kg/injection) and MDMA (0.01–0.56mg/kg/injection) were substituted for the training dose of cocaine for at least five consecutive sessions. Both cocaine and MDMA functioned as reinforcers, but self-administration of MDMA occurred at fewer doses and a significantly lower peak BP was obtained for MDMA. These data demonstrate that MDMA functions as a reinforcer, although its reinforcing efficacy appears to be less than that of cocaine.