The role of central monoamines in the genetically determined influences on voluntary ethanol consumption were examined by studying the extracellular levels of monoamines in the nucleus accumbens of the alcohol-preferring AA (Alko Alcohol) and alcohol-avoiding ANA (Alko Nonalcohol) rats with in vivo microdialysis. Dialysate samples for the assay of monoamines with small bore HPLC were collected from freely moving animals at 15 min intervals after administration of ethanol (0.5, 1, or 2 g/kg, i.p.). Ethanol significantly increased the extracellular levels of dopamine, DOPAC, and HVA, suggesting stimulation of dopamine release by ethanol, while the effect on 5-HIAA did not reach significance. No difference in the extent or time course of stimulation of dopamine release between the AA and ANA rats was found. The results could so far give no indication that the differential ethanol consumption by AA and ANA rats could be explained in terms of differences in ethanol-induced stimulation of dopamine release in the nucleus accumbens.