Tribolium castaneum (Herbst) adults and larvae and Plodia interpunctella (Huebner) larvae were exposed for 7 and 14 days to conditioned binary and ternary mixtures of nitrogen, oxygen, and carbon dioxide at 15 6, 26 7 and 37 8 degrees C. The moth larvae were more susceptible to changes in the atmospheric gas concentrations and high temperatures than the beetle adults or larvae. In general, mortalities increased by extending the exposure from 7 to 14 days, increasing the temperature from 15 6 to 37 8 degrees C, decreasing the oxygen concentration within binary or ternary mixture, or increasing the carbon dioxide concentration. Apparently, atmospheres lethal to the test insects can contain up to 15 % of oxygen if about 36% of the carbon dioxide is also present. In the absence of carbon dioxide, lethal atmospheres were obtained when the oxygen was reduced to about 1%.