D10 values obtained for radiation alone in Bacillus subtilis and Clostridium perfrigenes were 0.35-0.48 kGy in vegetative cells, and 2~2.08 kGy in spores, respectively. Irradiation dose of 24 kGy completely inhibited spores. In the case of heat treatment, D50, 60 values ranged from 10 to 14 minutes in vegetative cells, and D70, 80, 90 values ranged from 10 to 140 minutes in spores. In the case of combined treatment with heat and radiation, D10 values ranged form 1 to 1.25 kGy in vegetative cells, and from 3.42 to 3.61 kGy in spores. Thus, resistance of cells to gamma radiation did not seem to be influences by pre-heating.