Brain microdialysis was used to measure nucleus accumbens (NAC) ethanol (EtOH) over several hours after intraperitoneal (i.p.) injection of EtOH. Levels of EtOH in NAC perfusates were assayed by gas chromatography Peak EtOH levels were observed 40 min after the injection and the three doses of EtOH, 0.5, 1.0, and 2.0 g/kg, resulted in peak perfusate levels of 5 mM, 18 mM, and 38 mM, respectively. Measurement of regional brain EtOH levels may prove useful for studying the relationship between patterns of alcohol consumption and the action of EtOH in the central nervous system.