Batch cultures of a mouse/mouse hybridoma cell line secreting a dimeric IgA were performed in combination with a membrane process for the continuous removal of ammonia from the culture medium. The latter involves hydrophobic porous membranes with an associated pH gradient. The process was shown to be efficient reducing the ammonia concentration by approximately 50% by comparison to control experiments. Two series of experiments were performed with an initial glutamine concentration of 4 mM and 10 mM, respectively. The growth characteristics, antibody productivity, and quality of antibody assayed by Western blotting were not changed by ammonia removal; however, the cellular energy metabolism was affected by reduction of ammonia levels. Ar the lower initial glutamine concentration, ammonia removal caused an increased glutamine consumption and reduced lactate production. No effect upon glucose uptake was observed, thus resulting in a considerably reduced yield of lactate from glucose. At the high initial glutamine concentration, the reduced ammonia concentration led to a decrease in glucose and glutamine consumption as well as lactate production. This resulted in only a slight increase in the yield of lactate from glucose. Despite the abundance of literature concerning ammonia inhibition of mammalian cell cultures, little has been reported concerning the effect of continuous ammonia removal from such cultures.