Effects of a wide range of dissolved oxygen concentration (DO, 0.5-28 mg/l on anchorage-dependent BHK cell growth, metabolism and tPA production were examined with both serum-containing and serum-free media. In the range of DO from 0.5 to 5 mg/l, tPA production increased with an increase in DO in both media. Cell growth was higher at 5 mg/l DO than that at 0.5 or 2 mg/l DO in serum-containing medium, but it did not vary in serum-free medium in this DO range. Further investigation under hyperoxic conditions (DO >6.8 mg/l) revealed that specific rates of tPA production were enhanced by 2-fold in serum-containing and 1.7-fold in serum-free media, although cell growth depressed above 5 mg/l of DO. Slight increases in specific rates of lactate accumulation and glucose consumption were observed in both media under hyperoxic conditions. In serum-free medium, cells were found to be less tolerant to hyperoxic conditions than those in serum-containing medium. A DO shift-up with shifting time of 4 h in serum-containing medium was found to influence significantly both cell growth and tPA production.