Inshell peanuts infested initially with Tribolium castaneum (Herbst) adults were exposed 3 days at 26.7± 2 C to a mixture of approximately 46per thousand carbon dioxide, 11per thousand oxygen, and 43per thousand nitrogen at relative humidities of 71, 54, 33, and 8per thousand. At 33per thousand or less relative humidity this atmosphere was highly lethal to the adults and their progeny outside the cracked pods of peanuts. However, a humidity as low as 8per thousand had to be maintained before the atmosphere produced a mortality of 74per thousand among the insects inside the cracked pods.