A proper fumigant should be selected from the viewpoint not only of effectiveness but also chemical effects on cultural properties. Stains due to liquid fumigants are avoidable by the use of an evaporator. The important point in fumigation is not the total amount of the fumigant, but to keep an effective concentration for fixed hours. By the use of biological indicators, the proper concentration of the fumigant is controlled and an effective sterilization can be achieved.