Studies were performed on strain L cells grown in glass Petri dishes containing Eagle's MEM with Earle's BSS. The Petri dish cultures were held in a non-continuous flow gas chamber that was intermittently gassed with 95 per cent air (or O2)-5 per cent CO2. Using this system it was found that: A 95 per cent air-5 per cent CO2 atmosphere supported the growth of the cells in a typical logarithmic manner, with a generation time of about 24 h. The pH of the growth medium was maintained between 7.2-7.4. A significant growth inhibitory effect on cells exposed to high levels of oxygen (95 per cent O2-5 per cent CO2). The main advantage of the technique is that it requires only a small amount of gas and is, therefore, inexpensive to operate. © 1968.