In the present research the role of gender in MDMA-induced hyperthermia and serotonin depletion is studied by injecting male and female male rats with MDMA or saline 3 times (i.p.) with 3h interval at dosages of 0.3, 1, 3 or 9 mg/kg at an ambient temperature of 25°C. The acute hyperthermia following the higher dosages was much stronger in males than in females. After the highest dose, body temperature was even raised for several days. This effect was particularly present in males where nocturnal hyperthermia persisted the whole 4-week period of sampling. Despite the differences in the acute hyperthermic response, no significant gender differences were found in 5-HT depletion 4 weeks after MDMA (9 mg/kg) administration. A striking difference was present, however, in the concentration of the 5-HT metabolite 5-HIAA after MDMA administration. In males 5-HIAA levels decreased, whereas in females this metabolite was hardly affected, suggesting a lasting increase in 5-HT turnover in females following drug administration. When genders were matched for their acute physiological hyperthermic response by repeated injection of 9 mg/kg in female rats and 6 mg/kg in male rats, 5-HT depletion was only present in females. In this experiment with matched acute physiological responses 5-HIAA levels also decreased much stronger in males, suggesting an increased 5-HT turnover in females 4 weeks after MDMA administration. In conclusion, although male rats are clearly more susceptible for the acute as well as the lasting hyperthermic effects of MDMA than females, this is not reflected in levels of 5-HT depletion following administration of similar dosages of the drug. This may indicate that, in case of a similar thermogenic response, females have a higher 5-HT neurotoxicity following MDMA than males.