MDMA self-administration was examined in drug-naïve and cocaine-trained rats, with all rats receiving MDMA i.p. through a surgically implanted jugular catheter. Self-administration occurred in an operant chamber with an active (drug) and inactive (no drug) lever. Prior to MDMA-self administration, cocaine-trained rats underwent 5 to 12 2-hour long daily tests, with each drug lever press earning 0.5 mg/kg cocaine. Drug naïve rats could earn 1 mg/kg MDMA per lever press during daily acquisition trials (11 in all) that lasted for 2 or 6 hours. (Data from 2-hour and 6-hour sessions were later combined due to lack of session duration effect). The first dose was experimenter-administered. Rats in the 6-hour session condition next received 0.5 mg/kg per response MDMA for 8 days, and then saline was substituted for MDMA on the next 2 test days, with sessions lasting 2 hours. (No further information is provided on rats trained with 2-hour sessions). After saline sessions, MDMA (0.5 mg/kg per response) was reinstated in 2-h sessions. Apparently, cocaine trained rats received only 6-hour self-administration sessions with 1 mg/kg MDMA. The self-administration dose-response relationship was investigated by first providing 2 mg/kg MDMA per response during two daily 2-h sessions, and then subsequently decreasing available dose by half (2, 1, 0.5, 0.25), with each dose tested on 2 consecutive days. Response on the MDMA (active) lever was low for the first six days of acquisition (in drug-naïve rats), and a preference for the MDMA lever developed from the seventh to the 11^th daily session. Rats pressed the MDMA lever more frequently when dosage was reduced from 1 mg/kg to 0.5 mg/kg per response, and rats pressed the MDMA lever even less often when saline was substituted for MDMA. It appears that rats tried to accumulate a dose of 20 mg/kg per session, making an increased number of drug lever presses throughout sessions with lower doses. At higher doses, rats mostly pressed the drug lever at beginning of the session, with very few presses seen afterwards. MDMA lever pressing declined after saline substitution, and returned on MDMA reinstatement. Cocaine-trained rats were more likely to press the MDMA lever than were drug-naïve rats during the first 6 sessions. 2 mg/kg MDMA per press produced the lowest number of lever presses and 0.25 mg/kg MDMA the greatest number. During the 24-hour session, response on the active lever was largely seen during the first hours of the session. (One rat died at 11.5 h, for undisclosed reasons). This is the second paper reporting MDMA self-administration in rats (Ratzenboeck et al. 2001). The previous study reported lower response rates, with rats making an average of only two to four presses per session. The current report found that prior experience with cocaine increased rate of MDMA self-administration, just as prior experience with MDMA may enhance the rewarding properties of cocaine (Calloway and Geyer 1992; Fone et al. 2002, but see also Cole et al. 2003). However, it is possible that prior exposure to drug self administration procedures may have facilitated learning to self-administer another drug. Study findings reported here are among several reports suggesting that MDMA has abuse liability in mammals. It should be noted that studies in humans have already detected abuse liability (for example Jansen 1995; Lieb et al. 2002; Topp et al. 1999).