The effects of intraperitoneal administration of ethanol, 0.5, 1.0, and 2.0 g/kg body weight, on the extracellular concentrations of dopamine (DA), serotonin (5‐HT), and their major metabolites were studied in the nucleus accumbens (ACC) of alcohol‐naive, selectively bred high‐alcohol‐drinking (HAD) and low‐alcohol‐drinking (LAD) lines of rats using the technique of microdialysis. In both lines, the extracellular levels of DA were increased following the injection of 1.0 and 2.0 g of ethanol/kg body weight while only the 2.0‐g/kg dose elevated the concentration of 5‐HT. None of the ethanol doses altered the extracellular levels of the major metabolites of DA and 5‐HT. Dose‐response curves for DA and 5‐HT release indicated no marked difference in the sensitivity to ethanol between the lines. Local perfusion with 60 mM K⁺ through the microdialysis probe markedly enhanced the release of DA and 5‐HT in the ACC of both lines; there was a small difference between the lines in the amounts of DA, but not 5‐HT, released by K⁺‐stimulation. Overall, the results indicate that (1) the ACC DA system is more sensitive than the ACC 5‐HT system to intraperitoneal ethanol administration in both lines and (2) there is no evidence for a relationship between alcohol preference and sensitivity of the ACC DA and 5‐HT systems to acute intraperitoneal ethanol administration.