Basic information about medium-chain alcohol dehydrogenases of chordate animals and humans is presented. The publication consists of 6 chapters , Information about the structure , regulation and function of the enzyme , the structural and functional classification of human medium-chain alcohol dehydrogenase , The main parameters of evolutionary changes in alcohol dehydrogenase , encoding their mRNAs and corresponding genes. Particular attention is paid to the study of the nature of amino acid substitutions , Identification and analysis of hypervariable regions , Evaluation of the effect of mutational pressure on protein coding strategy and amino acid composition , as well as the quantitative relationship of the rates of evolutionary changes of mRNA with the neutrality of nucleotide substitutions in them. It is intended for biochemists, doctors and biologists interested in alcohol dehydrogenases and the problems of evolutionary changes of genetic macromolecules.