Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) exhibit genetic polymorphism and tissue specificity. ADH and ALDH isozyme phenotypes from 39 surgical Chinese lung specimens were identified by agarose isoelectric focusing. The identity of the lung beta-ADHs was further demonstrated by their characteristic pH-activity profiles for ethanol oxidation, Km values for NAD and ethanol, and inhibition by 4-methylpyrazole or 1,10-phenanthroline. The beta 2 allele, coding for beta 2 polypeptide, was found to be predominant in the lung specimens studied. The ADH activities in the lungs with the homozygous phenotype ADH2 2-2 (exhibiting beta 2 beta 2) and ADH2 1-1 (exhibiting beta 1 beta 1) and the heterozygous phenotype ADH2 2-1 (exhibiting beta 2 beta 2, beta 2 beta 1, and beta 1 beta 1) were determined to be 999 +/- 77, 48 +/- 17, and 494 +/- 61 nmol/min/g tissue, respectively. Fifty-one percent of the specimens studied lacked the ALDH2 activity band on the isoelectric focusing gels. The activities in the lung tissues with the ALDH2-active phenotype and the inactive phenotype were determined to be 30 +/- 3 and 17 +/- 1 nmol/min/g tissue, respectively. These findings indicate that human pulmonary ethanol-metabolizing activities differ significantly with respect to genetic polymorphism at both the ADH2 and the ALDH2 loci. The results suggest that individuals with high Vmax beta 2-ADH and deficient in low-Km mitochondrial ALDH2, accounting for approximately 45% of the Chinese population, may end up with acetaldehyde accumulation during alcohol consumption, rendering them vulnerable to tissue injury caused by this highly reactive and toxic metabolite.