Livers of rabbits contain three classes of alcohol dehydrogenase (ADH) isozymes which are highly analogous to the human classes. Class I ADHs migrate toward cathode on starch gel and are very sensitive to 4-methylpyrazole (4-MePz) inhibition. Class II ADH migrates slowly toward anode and is less sensitive to 4-MePz. Class III ADH migrates rapidly toward anode and is insensitive to 4-MePz. There are one class II, one class III and at least three class I ADH isozymes present in the rabbit liver. The three class I isozymes purified to homogeneity are all dimers with subunit molecular weight of 41700. Two are heterodimers composed of A-, C-chains and B-, C-chains, respectively. The third one is a homodimer, contains only the C-chain. These results indicate that among all the mammals examined, rabbit ADH bears the greatest resemblance to the human enzyme.