Liver cytosolic aldehyde dehydrogenases (AHD-2) have been isolated in a highly purified state from "alcohol-drinking" (C57BL/6J) and "alcohol-avoiding" (DBA/2J) strains of mice. The purified enzymes were resolved into three major and one minor form of activity by isoelectric focusing (IEF) techniques and showed similar zymogram patterns. The enzymes had identical subunit sizes on SDS-polyacrylamide gels: 53,000. Gel exclusion chromatography, using Ultrogel AcA34, indicated that the enzymes were dimers. The enzymes exhibited biphasic kinetic characteristics and were readily distinguished from each other. The purified forms of AHD-2 from C57BL/6J and DBA/2J mice exhibited two apparent Km values in each case: 10 microM/100 microM and 30 microM/330 microM respectively. AHD-2 exhibited a broad pH optimum in the range 7.0-9.0 and was very sensitive towards disulphuram inhibition, with 50% inhibition occurring at 0.17 microM. The kinetic results support proposals that AHD-2 may be the primary enzyme for oxidizing acetaldehyde during ethanol oxidation in vivo.