The gamma-irradiation decreased the amt. of SH group of the cysteine, urease, glutamic and alcohol dehydrogenase molecule linearly with increasing doses. The presence of catalase decreased the gamma-ray inactivation of those enzymes. With use of yeast alcohol dehydrogenase the proportion of inactivation by H2O2, OH free radical and HO2 free radical were calcd. as 24.2, 46.5 and 29.3%, resp.