The magnitude, direction, and time course of the effects of acute administration of ethanol (0.1 or 1.0 g/kg) on the extracellular levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and GABA within the nucleus accumbens of the rat were analysed using microdialysis in conjunction with high-pressure liquid chromatography and electrochemical detection. IP injection of 0.1 g/kg ethanol failed to modify the extracellular concentration of DA, DOPAC, HVA, 5-HT, 5-HIAA, and GABA in the nucleus accumbens during the 120-min collection period. On the contrary, 1.0 g/kg IP ethanol significantly increased extracellular levels of DA, DOPAC, and 5-HIAA in microdialysates from the nucleus accumbens. The maximal increase in DA (314.87 +/- 6%), DOPAC (210.58 +/- 3%), and 5-HIAA (250.88 +/- 8%) was observed 40 min after administration of ethanol. Extracellular HVA was also enhanced (220.89 +/- 2%) at time point 100 min following injection of the same dose of ethanol. Finally, extracellular levels of 5-HT and GABA remained unchanged following 1.0 g/kg ethanol.