Effects of dissolved oxygen concentration (DO) on anchorage-dependent cell growth, cell metabolism, and erythropoietin (EPO) production were investigated in both serum free and serum containing media. Specific EPO production rate increased significantly with the increase in DO from low to high levels with both media. Culture with serum free medium was found to be more dependent on DO than that with serum containing medium. The specific rates of cell growth and EPO production with controlling DO at 5.0 mg/l were 3.5- and 2.5- folds higher, respectively, than those with controlling DO at 0.5 mg/l. However, in serum containing medium, the specific growth rate was hardly influenced by DO levels, whereas the specific EPO production rate was 1.4-fold repressed under low DO levels. Influences of accumulated lactate and ammonium ion were negligible in the DO-controlled cultivation.