Replicatively senescent cells of Saccharomyces cerevisiae were obtained using the 'baby machine' method by immobilizing cells on CovaLink NH(2) plates and allowing them to divide while exchanging medium and removing daughter cells. Centrifugation in a Percoll density gradient was employed for further purification of replicatively old yeast cells. Comparison of senescent cells showing more than 20 bud scars with cells from early stationary culture demonstrated a significant reduction of total and reduced glutathione and decrease of superoxide dismutase activity during replicative aging of yeast cells.