A recombinant CHO cell line, CHO2DS, was immobilized on porous microcarrier Cytopore 1 and cultivated in 1 l modified Super-spinner and 2 l stirred tank bioreactor with the perfusion of a low-cost chemically defined protein-free medium DF6S. CHO2DS cells could enter into the inner space and grew both in the inner space and on the surface of Cytopore 1 in DF6S and produced prothrombin at 22 mg l(-1) after 10 days. From a seeding density of 5.7 x 10(5) cells ml(-)1, the highest viable cell density of CHO2DS was 1.12 x 10(7) cells ml(-1).