A number of factors have been shown to affect the metabolism of glucose and glutamine in mammalian cells and their mechanisms have been partially elucidated. Despite these efforts, a quantitative knowledge of the significance of these factors, the regulation of glucose and glutamine utilization, and particularly the interactions of these two nutrients is still lacking. Controversies exist in the literature. To clarify some of these controversies, mathematical models are proposed in this work which enable to separate and identify the effects of individual factors. Experimental data from five cell lines obtained in batch, fed-batch, and continuous cultures, both under steady-state and transient conditions, were used to verify the model formulations. The resulting kinetic models successfully describe all these cultures. According to the models, the specific consumption rate of glucose (q(Glc)) of continuous animal cells under normal culture conditions can be expressed as a sum of three parts : a part owing to cell growth; a part owing to glucose excess; and a part owing to glutamine regulation. The specific consumption rate of glutamine (q(Gln)) can be expressed as a sum of only two parts : a part owing to cell growth; and a part : owing to glutamine excess. Using the kinetic models the interaction and regulation of glucose and glutamine utilizations are quantitatively analyzed. The results indicate that, whereas q(Glc) is affected by glutamine, q(Gln) appears to be not or less significantly affected by glucose. It is also shown that the relative utilizations of glucose and glutamine by anabolism and catabolism are mainly affected by the residual concentrations of the respective compounds and are less sensitive to growth rate and the nature of growth limitation.