A problem in the mass production of recombinant proteins and biopesticides using insect cell culture is CO2 accumulation. This research investigated the effect of elevated CO2 concentration on insect cell growth and metabolism. Spodoptera frugiperda Sf-9 insect cells were grown at 20% air saturation, 27(degrees)C, and a pH of 6.2. The cells were exposed to a constant CO2 concentration by purging the medium with CO2 and the headspace with air. The population doubling time (PDT) of Sf-9 cells increased with increasing CO2 concentration. Specifically, the PDT for 0-37, 73, 147, 183, and 220 mm Hg CO2 concentrations were 23.2 +/- 6.7, 32.4 +/- 7.2, 38.1 +/- 13.3, 42.9 +/- 5.4, and 69.3 +/- 35.9 h (n=3 or 4, 95% confidence level), respectively. The viability of cells in all experiments was above 90%, i.e., while increased CO2 concentrations inhibited cell growth, it did not affect cell viability. The osmolality for all bioreactor experiments was observed to be 300-360 mOsm/kg, a range that is known to have a negligible effect on insect cell culture. Elevated CO2 concentration did not significantly alter the cell specific glucose consumption rate (2.5-3.2 x 10(-17) mol/cells), but slightly increased the specific lactate production rate from -3.0 x 10(-19) to 10.2 x 10(-19) mol/cells. Oxidative stress did not contribute to CO2 inhibition in uninfected Sf-9 cells as no significant increase in the levels of lipid hydroperoxide and protein carbonyl concentrations was discovered at elevated CO2 concentration. (c) 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:465-469, 2016