New molecular forms of human liver alcohol dehydrogenase (ADH), collectively designed ADH Indianapolis (ADHInd), were recently discovered in 29% of liver specimens from Black Americans [Bosron, W. F., Li, T.-K., and Vallee, B. L. (1981). Proc. Natl. Acad.Sci. USA 77:5784]. Three different ADHInd phenotypes have now been identified by starch gel electrophoresis, and four ADHInd enzyme forms isolated by affinity and ion-exchange chromatography. The most cathodic ADHInd form has a single pH optimum at 7.0 for ethanol oxidation and is a homodimer of a newly discovered subunit, as evidenced by dissociation--recombination studies. The remaining three purified ADHInd forms have dual pH optima for ethanol oxidation at 7.0 and 10.0 and generate two new bands on starch gel electrophoresis after dissociation-recombination. They appear to be heterodimers of this new subunit with the known subunits, alpha, beta 1, and gamma 1. Based on the occurrence of these four ADHInd isozymes and isozymes containing beta 1 subunits in the homogenate supernatants of 135 livers, we conclude that ADHInd results from polymorphism at the ADH2 locus, with the variant ADH2Ind allele coding for the beta Ind subunit. The frequency of ADH2Ind was 0.16 in Black Americans. The frequency of the ADH31 and ADH32 alleles also differed in these two populations.