In order to establish a cell line suitable for a hybrid artificial liver support system, an ammonia metabolizing activity is given to a Chinese Hamster Ovary (CHO) cell line using genetic engineering techniques. CHO-K1 cells were transformed with pSV 2-GS vector which contain glutamine synthetase gene connected with SV 40 promoter. The recombinant cell line was selected under various concentrations of glutamine synthetase inhibitor, methionine sulfoximine (MSX). The 800 mu M MSX tolerable cell line has high glutamine synthetase activity and can remove ammonium from the medium. The kinetic parameters of this cell line were investigated under 0, 1, or 2 mM ammonia concentration. Ammonia consumption occurred during the middle phase of cultivation (growth phase). The specific ammonium consumption rate of the established cell line during growth phase is about one fifth of that of primary hepatocyte.