This study was carried out to determine whether concentrations of the brain monoamines noradrenaline (NA), dopamine (DA), and 5-hydroxytryptamine or serotonin (5-HT) are different in three inbred strains of mice (C57BL/6J, C3H/He and DBA/2Cr) known to differ in their preference to alcohol, when they were given a free choice of 10% (v/v) ethanol and tap water to drink for 4 weeks. Mice of these three strains showed mean ethanol intakes of 4.41, 1.76 and 0.77 g/kg/day respectively. Levels of the above brain monoamines did not change in the alcohol-preferring C57BL/6J mice, but in those with less preference for alcohol, C3H/He and DBA/2Cr, there were significant increases in DA and 5-HT levels respectively during the 4-week experiment. These findings suggest that inbred strains of mice show genetic differences of susceptibility to ethanol and that the strains with a low preference for alcohol undergo neurochemical changes after exposure to 10% ethanol and water even by free choice.