In laboratory experiments, egg, larval, pupal, and adult stages of the red flour beetle Tribolium castaneum (Herbst) were exposed to three low oxygen concentrations realistically obtainable under hermetic storage conditions, at three temperatures of 26, 30, and 35°C. The gas concentrations were: 1% O2, 85% N2, 14% CO2; 2% O2, 84.7% N2, 13.3% CO2; 3% O2, 85% N2, 12% CO2 (all at 75% relative humidity). When exposed to the 3% O2 level at 26°C, adults were most tolerant with a mortality of 70.5% when exposed for 10 d. To obtain 99% mortality at 35°C with the atmosphere containing 1% O2, a maximum of only 44 h was required for the most tolerant stage, namely the pupa. Comparison of exposure times required to produce 50% kill (LT50) showed that the effect of temperature on mortality rates was pronounced at all three levels of O2; for all the insect stages, values of LT50 at 35°C ranged between 0.16 and 0.5 times those at 26°C. The insects were also submitted to a gas mixture containing 1% O2 in 99% N2 representing a mixture obtainable by N2 flushing techniques. At the higher temperatures, differences in mortality from those obtained on exposure to 1% O2:85% N2:14% CO2 were not significant. However, at 26°C, mortality levels of insects exposed to this mixture were lower, particularly for adults and eggs.