A stress-free, biotelemetric monitoring technique was used to investigate the effects of ambient temperature (Ta) on the hyperthermic and hyperkinetic effects of 3,4-methylenedioxymethamphetamine. In the first experiment a single injection of 5.0 or 7.5 mg/kg MDMA produced hyperthermia in rats maintained at a Ta of 24 degrees C but hypothermia in rats maintained at a Ta of 11 degrees C for 24 h prior to the injection. In contrast, hyperkinesis was induced at both Tas. In the second experiment, the effects of acute MDMA administration was compared in rats maintained at a standard Ta of 24 degrees C and in rats which were placed in a cool (11 degrees C) room for a brief (90-min) period commencing 30 min after the injection. The brief exposure to the cool environment produced significant attenuation of MDMA-induced hyperthermia but did not affect the magnitude of hyperkinesis. The implications of the results for the understanding of the thermotoxic effects of MDMA in human drug users are discussed.