Young male Lister Hooded rats given MDMA starting on post-natal day 39 (7.5 mg/kg twice daily in 3 consecutive days) initiated fewer social interactions with another rat, and exhibited an enhanced preference for a place associated with cocaine injection when compared with saline-treated rats. Despite these long-term behavioral changes, there were no indications of decreased 5HT or 3H-paroxetine binding in frontal, hippocampal and brain stem extracts taken from rats sacrificed 24 d post-drug. (These animals did not undergo the conditioned place preference procedure and did not receive cocaine). Conditioned place preference was not produced in saline-treated rats. These findings suggest that demonstrably non-neurotoxic doses of MDMA may induce long-term behavioral changes in rats, and perhaps in humans as well, but conversely, that this long-term behavioral change cannot serve as an indicator of serotonergic neurotoxicity.