Previously by selection and inbreeding of Wistar rats susceptible or resistant to the cataractogenic effect of galactose the S and R rat strains were developed as a model of oxidative stress. It was earlier found S rats have elevated level of OH-radical generation and enhanced lipid peroxidation compared with that for R rats. Our data show that superoxide dismutase and catalase activities in the blood of S rats are twice lower than corresponding values of R rats. Increased level of disulfides and protein carbonyl groups was obtained in the blood plasma of S-rats. It was found that fluidity of erythrocyte membrane measured by photobleaching method is definitely higher for S rats compared with that for S rats. Similar effect of decreased catalase activity and increased disulfide content has been observed for kyphoscoliosis patients.