We have investigated that atmospheric stability in polystyrene and glass cell culture vessels by measuring the dissolved O2 and CO2 in the media of both seeded and unseeded culture vessels incubated at 37 degrees C. There was no diffusion of either O2 or CO2 through glass vessels. At low partial pressures of oxygen (PO2), oxygen diffused into the polystyrene flasks at a rate of 1 to 2 mmHg per 24 hr, and at high PO2, oxygen diffused slowly out of polystyrene flasks. CO2 diffused out of polystyrene flasks with a half-time of 260 hr resulting in a considerable elevation in pH. In seeded polystyrene flasks with the PO2 less than or equal to room air, cellular oxygen consumption was masked by the inward diffusion of oxygen. In addition, the fall in pH due to metabolic CO2 and organic acid production during cell growth in polystyrene flasks was buffered by the diffusion of CO2 out of the vessels.