This study examined some acute pharmacological and toxicological effects of 3,4 methylenedioxymethamphetamine (MDMA, ''Ecstasy'') over a range of doses (20, 40, 80, 160 and 320 mg/kg orally) in adult female rats. Deaths were observed from the 40 mg/kg MDMA group onwards. Reductions in body weight change, food and water intake were found in the 80 mg/kg group, whilst food intake alone was reduced in the 20 and 40 mg/kg groups. Significant hyperthermic responses were found over the first 8 hr following MDMA administration which were dose-related. A significant hyperactivity of approximately 9 hr duration was observed in the 20 mg/kg and 40 mg/kg groups, whereas there was evidence of a serotonin syndrome in the higher dosage groups. Thus, acute oral administration of MDMA results in a variety of measurable responses. The cause of death in this study is probably a combination of serotonin syndrome and hyperthermia.