Oxygen consumption rates were measured in a respirometer for different mammalian cell lines (BHK, murine hybridoma, and CHO), and the effects of cell density (1-20 million cells/mL) and temperature (6 to 37 degrees C) on specific oxygen consumption rate were investigated. The specific oxygen consumption was cell line dependent. For a given temperature, the murine hybridoma cells had the lowest and the CHO cells had the highest oxygen consumption rate. The specific oxygen consumption rate was not affected by the cell concentration for cell densities between 1 and 20 million cells/mL. However, artificial trends implicating the effects of cell density were obtained when traditional analysis was used and the probe response time was neglected. A detailed mathematical analysis was presented to investigate the magnitude of errors originating from neglecting the probe response time for the calculation of oxygen consumption rate. The error was significant, especially when the probe response was slow and/or the oxygen consumption was fast. Temperature influenced the specific oxygen consumption rate similarly for the cells studied, and about 10% decrease was observed in specific oxygen consumption by 1 degrees C decrease in the temperature. Between 6 and 37 degrees C, the effect of temperature on oxygen consumption rate could be described using an Arrhenius model, i.e., q(O2) = q(O2)degrees . e(-E/RT). The activation energy, E, in this equation was similar for different cells (between 80 and 90 kJ/mol), indicating the action of a similar mechanism for the effect of temperature On oxygen consumption.