Adults of the red flour beetle, Tribolium castaneum (Herbst), and larvae of the Indian-meal moth, Plodia interpunctella (Hübner), were exposed 6 and 24 hours in towers containing peanuts being purged with CO2 or N2. Of the insects exposed for 6 hours, 2 groups had mortalities of 20 and 32per thousand, the other 46 groups less than 9per thousand. Twenty-four hours of purging with CO2 caused the greatest insect mortality. This mortality varied with age and species and was more than 90per thousand among the 9-day-old larvae.