Material and degree of reductance balance equations are used to estimate the rates of oxygen uptake and carbon dioxide evolution of animal cell cultures. Lumped compositions, molecular weight and reductance degree of cellular protein, monoclonal antibody, biomass and amino acid consumption (excluding glutamine and alanine) are found to be relatively constant for different hybridoma cell lines and may be used as regularities. The calculated rates of oxygen uptake and carbon dioxide evolution agree well with experimental values of several different cultures reported in the literature. This simple method gives the same results as calculated on the basis of a detailed metabolic reaction network.