Catalase and superoxide dismutase activities have been explored in the yeast Saccharomyces cerevisiae during batchwise growth experiment. During the diauxic growth in YPD medium high Ys values were obtained (0.415 - 0.423) and correlation between the total activities of both enzymes has been found. A mitochondrial fraction from three type strains of Saccharomyces cerevisiae has been isolated. The purity of this fraction was proved through different enzyme assays: hexokinase, glucose-6-phosphate dehydrogenase, D-amino acid oxidase, isocitric lyase, succinate dehydrogenase. Then the catalase, peroxidase, Mn and Cu/Zn superoxide dismutase activities were evaluated in the mitochondrial fraction. Polyacrylamide gel electrophoresis separations allowed to identify a mitochondrial catalase as a band of 0.239 Rm value. It differed from the two catalase specific bands with Rm values 0.218 and 0.257 obtained from the crude extract. It was proved that the three catalase proteins are charge isomers. A positive correlation between the activity of mitochondrial catalase and Mn superoxide dismutase also takes place. Molecular weight of mitochonrial catalase protein has been determined as 240 kD.