Using a Saccharomyces cerevisiae ADH1 probe, a gene coding for a cytoplasmic alcohol dehydrogenase from Kluyveromyces marxianus ATCC 12424 (formerly K. fragilis) has been cloned. This gene is able to restore alcoholic fermentation in an ADH-null strain of S. cerevisiae and its encoded protein shows strong similarity with other yeast alcohol dehydrogenases (from S. cerevisiae, Schizosaccharomyces pombe and its close relative K. lactis). The product of the gene expressed in S. cerevisiae co-migrates on native gel with a K. marxianus ADH isozyme which is more active in cells growing on non-fermentable carbon sources than on glucose. This behaviour is in contrast with that of the two cytoplasmic ADH isozymes of K. lactis which are both more active in glucose-growing than in ethanol-growing cells.