[en] Adults of Tribolium confusum duv., were subjected to several concentrations of CO₂ in air and then exposed to gamma irradiation one day and 7 days later. The beetles became more radiosensitive when exposed to CO₂ followed by irradiation within 24 hour. This effect started to appear 7 days after irradiation in the treatments of the highest CO₂ concentration (46%) and 10 or more krad., increased after 14 days and reached to almost complete mortality after 21 days. On the other hand, exposure of the insects to CO₂ and then to irradiation after 7 days did not show any effect. Slight effect began to appear after 14 days and did not reach complete mortality after 21 days, except at the highest concentration of CO₂ followed by treatment with 20 krad or more. Thus, irradiation of the beetles within 24 hr. after exposure to CO was more effective than within 7 days. Generally, the treatments of CO₂ followed by gamma irradiation induced higher percent mortality than either treatment applied alone.3 tab