Yeast S. cerevisiae, are sources of high and low molecular weight biologically active substances. They are widely used in the biotechnology and in food technologies. Previously it was found that under conditions of refrigeration storage content of low molecular SH- groups in baking yeast is increased, but this result requires explanation. Evaluation of the redox potential in different strains of industrial yeast is of great interest, however in literature such data are not available. The calculation of Eo′ in thioldisulfid system of different industrial yeast strains has been made. No indicator variations in the strains has been shown to exist. By comparing redox potential of laboratory cultures to the one of compressed baker's yeast a higher values of Eo have been found ′ in the cells of the former. The theoretical and practical significance of the results obtained is discussed.