The effects of glutamine on cell growth kinetics, monoclonal antibody productivity, and cell metabolism of hybridoma cells were investigated. The mouse-mouse hybridoma cell line VIII H-8, which produces mouse immunoglobulin (IgG(2a)) was used as a model system. Glutamine showed a Monod-type effect on specific cell growth rate with a very small Monod constant of 0.089 (mM). A reciprocal relationship between initial glutamine concentration and specific cell death rate was observed. Monoclonal antibody (MAb) production was a strong function of glutamine concentration. Glutamine enhanced MAb production not only by stimulation of cell growth, brit also by increasing the specific MAb productivity. Increasing glutamine concentration stimulated specific glutamine consumption rate and specific ammonium ion production rate. The specific glucose consumption rate decreased with increasing glutamine concentration up from 0 to 0.1 mM, and then increased. The specific lactate production rate decreased as glutamine concentration decreased.