Ecstasy [(±) -3-4-methylenedioxymethamphetamine, MDMA] is a widely abused drug which in overdose can lead to serotonin syndrome. The patient presents with agitation, tremors, and muscle spasms, followed by hyperthermia whichcan lead to fatal organ failure. Recently ecstasy tablets have been found to contain piperazines, particularly 1-benzylpiperazine (BZP). The purpose of cutting ecstasy with BZP is to enhance the psychostimulant effects of MDMA. BZP is also marketed as a "legal high" in some countries; therefore some ecstasy tablets contain solely BZP. BZP is the active metabolite of an antidepressant drug, trelibet, which failed in clinical trials. There has been little study on the pharmacological effects of combining BZP with MDMA so we have investigated the bioavailability, neurochemistry and behavioral profile of these drugs administered alone or in combination in rats. We have used the technique of brain microdialysis in rat frontal cortex, to monitor extracellular levels of noradrenaline, dopamine and serotonin in response to peripheral administration of BZP and MDMA. We were also able to monitor the animals for evidence of rodent serotonin syndrome. BZP (10mg/kg, i.p.) was able to elevate extracellular levels of dopamine, noradrenaline and to a lesser extent, extracellular serotonin in rat frontal cortex. MDMA (3mg/kg, i.p.) potently elevated extracellular serotonin and noradrenaline and to a lesser extent extracellular dopamine in frontal cortex. These neurochemical effects lasted for at least 2 to 3 hours relative to salinetreated control animals. Combined BZP and MDMA administration led to markedly elevated extracellular levels of all three monoamines indicating the effects of the drugs were additive. BZP (10mg/kg, i.p.) caused marked behavioral activation, for example, increased locomotor activity and rearing behavior, whereas MDMA (3mg/kg, i.p.) resulted in flat body posture and less rearing. Similar to MDMA (3mg/kg, i.p.), BZP increased grooming, forepaw treading, sniffing and head weaving relative to saline injected animals. We also investigated a 5-HT2A receptor antagonist, ketanserin (3mg/kg i.p.), to see if it could attenuate BZP-induced behaviors. Ketanserin alone had little effect on rat behavior but when co-administered with BZP, was able to decrease locomotion and rearing behavior. Interestingly, ketanserin had little effect on the increased sniffing and head weaving induced by BZP. At the doses of drugs used in this study hyperthermia was not apparent in any of the animals but we were able to measure blood and brain levels of BZP and MDMA hence we know bioavailability was not a problem. Overall, these results suggest that BZP and MDMA share certain psychopharmacological and neurochemical properties in the rat. Furthermore, combined administration of BZP with MDMA leads to a marked elevation of extracellularlevels of all three monoamines in the frontal cortex rather than just serotonin which, if translated into the clinical setting, may explain the agitation and sympathomimetic toxic syndrome reported in some patients. All animal studies were conducted in accordance with the Canadian Council on Animal Care Guidelines and Policies with approval from the Animal Care and Use Committee in Health Sciences for the University of Alberta. This work issupported with a grant from Canadian Institute of Health Sciences.