(+/-)3,4-methylenedioxymethamphetamine (MDMA; "Ecstasy"), an increasingly popular recreational drug, is known to damage brain serotonin (5-hydroxytryptamine [5-HT]) neurons, whilst also having a less pronounced effect on the dopaminergic system. Treatment with MDMA results in an increased locomotor activity, elevated basal serum corticosterone concentrations, decreased exploratory activity, and changes in body temperature. The aim of this study was to examine the dose related effects of subacute administration of MDMA (5, 10, and 20 mg/kg IP twice daily for 4 days) on home cage locomotor activity, "open field" and "step-down passive avoidance" behaviours, changes due to an 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) challenge, and on plasma corticosterone and brain neurotransmitter concentrations. Total locomotor activity counts were significantly increased by both 10 and 20 mg/kg MDMA for the 4 days of drug administration. There were no significant differences seen in the "open field" or "step down passive avoidance" behaviour, in the 8-OH-DPAT induced hypothermia, or in basal serum corticosterone concentrations. MDMA caused a significant depletion of both 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the frontal cortex and amygdala and a significant elevation of dopamine and noradrenaline in the hippocampus. Apart from the increase in locomotor activity following subacute administration, the observed behaviour of the MDMA treated rats would not appear to reflect the substantial changes in brain biogenic amine neurotransmitters.