Most of the radiobiological protectants reported in the past are effective when they are given during or just before irradiation, or when given in seriously toxic doses. Therefore, they will be of little value for practical use. On the view point of homeopathy, some positive results were reported in this field. But it should be avoided to use radiation as a pretreating agent because of its deleterious cumulative genetic effect. Stokinger et al. had discovered a phenomenon of “cross-tolerance” among ozone, nitrogen dioxide, etc. Ozone is known to be radiomimetic. So, we attempted to use ozone as a prechallenge treating agent.
A tolerance to x-radiation was rapidly developed (within 24 hours) by subjecting mice previously exposed to 1ppm of ozone for only one hour. Dose reduction factor at LD₅₀ was about 1.3. This tolerance lasted for at least 10 days and disappeared at about 50th day after exposure to ozone. These pretreated animals had no significant changes in body weight and blood picture, and they could swim for a long time equally as controls. This radiotolerance has such advantages as rapid development, long duration and good preservation of physical strength. This experiment may promise a future progress in the field of radiobiological protection.