To develop a novel and effective method for sterilization of bacterial spores, we examined the lethal effect of high-pressure CO2 on spore cells of Bacillus megaterium at various pressures and temperatures and for various treatment times. The bactericidal effect was found to be enhanced with increasing temperature and treatment time. Interestingly, there was an optimum pressure in the subcritical region of CO2 which gave the maximum inactivation effects. Under the appropriate conditions of 58 atm, 60 degrees C and 30 h, the survival ratio of the bacterial spore could be reduced to about 10(-7).