The objective of this study was to analyze fermentation activity and some genetic traits of mesophilic wine yeast strains representing two species: Saccharomyces cerevisiae and Saccharomyces bayanus. The yeast strains analyzed were characterized by a varying physiological activity. Statistical differences were to be attributed to the production of ethanol and glycerol, as well as to the SO₂ level and sugar consumption. Chemical properties of wine fulfilled the standard recommendations, thus, they proved the high technological usefulness of the strains examined. The yeasts were also characterized by a good ability to biodegrade L-malic acid under the anaerobic conditions, after the wine fermentation completed, and they reduced the content of this acid by 65,6 to 68,4%. The yeast strains tested showed a polymorphism of the genome’s DNA, and electrophoretic profiles of the chromosomal and mitochondrial DNA patterns differed in their number, location, and intensity of stripes. It was possible to unambiguously differentiate between individual wine yeast strains on the basis of genetic analysis applied simultaneously with two other techniques from the domains of molecular biology: karyotyping and mtDNA restriction analysis. The DNA contents in yeast cells as determined by a flow cytometry indicated that yeast strains were either diploid or aneuploid. Differences in the physiological and genetic properties of the yeast strains tested proved clear dissimilarities among them; however, those dissimilarities did not allow for the definite, taxonomical classification of the yeast strains to S. cerevisiae and S. bayanus groups; this fact may confirm the hybridization of yeast within a Saccharomyces group in a natural environment.