In this study, the susceptibility of larvae and adults of Tribolium castaneum (Herbst) to gamma radiation was investigated in the laboratory in Turkey. Gamma radiation was applied at 6 dose levels between 20 and 200 Gy to 13-15 day-old adults and at 5 dose levels between 20 and 180 Gy to 18-20 day-old larvae of T. castaneum. All experiments were performed in growth chambers maintained at 27+/-1degreesC and 70+/-5% r.h. The larvae proved to be the more susceptible stage, survival to the adult stage being prevented by exposure of the eggs to 100 Gy; the adult stage was less susceptible. LD50 and LD99 values were determined as 19,75 and 42,97 Gy for larvae and 33,21 and 64,50 Gy for adult stage, respectively. It was concluded that 100 Gy is the effective dose for both larval and adult stages.