Cocaine and cocaethylene (a psychoactive metabolite of concurrent cocaine and ethanol consumption) were studied in the anesthetized vervet monkey. The ability of each to elevate extracellular DA in the caudate nucleus was assessed using microdialysis probes acutely lowered through chronic guide cannulae. Blood samples were also collected to determine plasma levels of the two drugs. Doses of 1.5 mumol/kg cocaine (equivalent to 0.5 mg/kg cocaine-HCl) and cocaethylene were administered intravenously. Microdialysis and blood samples were collected at 5-min intervals immediately following drug administration. Both drugs caused a maximal four-fold increase in extracellular DA during the 5- to 10-min period following drug administration. This is the first report of cocaine (and cocaethylene) induced alterations in extracellular DA in primates. The abilities of cocaine and cocaethylene to produce euphoria are being compared in ongoing clinical research studies. The potential use of these results for interpreting the neurochemical basis of any differences in those studies is discussed.