Methylenedioxymethamphetamine (MDMA) has previously been shown to produce a positive conditioned place preference (CPP) among rats. Here the effects of doses of a specific 5-HT3 antagonist, MDL72222, on MDMA's ability to produce a CPP were assessed. A dose of MDL72222 (0.03 mg/kg) blocked the establishment of a MDMA CPP. These results support the suggestions that compounds affecting the 5-HT3 r...