A 3-liter culture vessel has been developed for the growth of animal cells in suspension at controlled pH and dissolved oxygen partial pressure (pO2). The culture technique allows metabolically produced CO2 to be measured; provision can be made to control the dissolved CO2 partial pressure. In cultures containing a low serum concentration, gas sparging to control pO2 was found to cause cell damage. This could be prevented by increasing the serum concentration to 10%, or by adding 0.02% of the surface-active polymer Pluronic F68. The growth of mouse LS cells in batch culture without pO2 control was found to be limited by the availability of oxygen. Maximum viable cell populations were obtained when dissolved pO2 was controlled at values within the range 40–100 mm Hg.