The relative ability of two commercial gas generating envelopes, the evacuation-replacement technique, and a candle jar, to produce a satisfactory microaerobic atmosphere for the culture of 45 Campylobacter strains on non-selective medium and five selective media (Skirrow's, modified Butzler's Blaser's, Campy-BAP and Preston medium) was investigated quantitatively. A candle jar, and modified Butzler's medium proved to be of limited use. The ability of four commercial gas generating envelopes to produce a satisfactory microaerobic atmosphere in four anaerobic jars of different volume was investigated using five reference Campylobacter strains. Not all of the combinations worked. The oxygen and carbon dioxide concentrations produced in the microaerobic systems studied were measured with gas analysers. The evacuation-replacement technique produced far less variable concentrations of oxygen and carbon dioxide than did the envelopes.