A Chinese hamster ovary (CHO) cell line producing a recombinant glycoprotein was cultured in batch mode with different initial concentrations of ammonium chloride (0-10 mM), sodium lactate (0-60 mM), or sodium chloride (0-60 mM). High ammonium concentrations did not inhibit cell growth and productivity or glucose and glutamine consumption. In contrast, specific ammonia and alanine production decreased by 55% and 40%, respectively. There were also significant increases in specific aspartate and glutamate consumption in high ammonium concentrations. These observations indicated a shift in glutamine catabolic pathways in response to the effects of ammonium. The influence of lactate on growth and metabolism were the combined effects of lactate concentration and osmolarity. After "correcting" for osmolarity effects, lactate was found to inhibit growth by 25% but to increase specific productivity slightly (10%). Lactate had profound effects not only on glycolysis but also on glutaminolysis. While specific glucose and glutamine consumptions decreased by 15-20%, the effects of lactate on their metabolic products were far more significant. Lactate production was halted, and specific ammonia and alanine productions decreased by 64% and 70% at high lactate concentration. Theories on how ammonium and lactate affected the metabolic pathways of glucose and glutamine are presented.