Introduction Sterilization is the backbone of the germ-free laboratory. Before they enter the isolators, hoods, or isocages, all materials must be completely free of bacteria, viruses, fungi, and any other microorganisms and must be kept sterile at all times. Any method of sterilization must be effective against not only viable bacteria but also bacterial and fungal spores, nonenveloped viruses, and so on. In short, sterilization must be absolute.