The lifetime research of the oxidized and methilated guanine's contents in urine of intact and radiated mice was carried out. For statistical processing of results we used the method of the trial periods. This method has been created by A.A. Konradov, but has not been published during a life of the author. It has allowed finding out oscillatory part of age-related dependences. For intact animals the most probable (p = 0.001) is the period of 7 months. The infringement of a seasonal rhythm of fluctuations of oxidized and methilated guanine's concentration in urine is marked for the radiated mice. It is specific feature of the radiation-accelerated ageing.