Microdialysis cannulas were surgically implanted into the striatum of thyroparathyroidectomized (TX) and sham rats in order to determine differences in dopamine release and core body temperature following MDMA administration. Rats were subsequently treated with MDMA (10 mg/kg, s.c.), and striatal DA levels were monitored at 20 min intervals, as well as core temperature every 30 min. Sham rats responded to MDMA with a characteristic hyperthermic response and significant increases in extracellular dopamine. Conversely, TX rats responded to MDMA with a hypothermic response and failed to demonstrate a similar increase from basal dopamine levels. On the basis of these data, thyroid hormones are not only important in the thermogenic effects of MDMA but also appear to have an auxiliary role in MDMA-induced striatal dopamine release.