Review is presented on the role of superoxide radicals and other intermediates of single electron reduction of oxygen in aging as well as on geroprotective importance of superoxide dismutase. These factors are considered in relation with age. Significance of direct and indirect methods for estimation of total O2-radicals is analyzed. Possible role of O2-radicals and superoxide dismutase in regulation of cell division and differentiation is also discussed. Life span of cells in peripheric circulation correlates with superoxide dismutase content in these cells and their ability to generate exogenous O2-.