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Statistical materials of recording the number of patients and of the typhoid-paratyphoid infections morbidity level in Russia and the USSR from 1891 to 1976 was studied. A stable tendency to reduction of this morbidity was noted. In analysing the empirical and flattened--by 3 and 5 points--curves of the number of patients and the morbidity level a regularity of declining morbidity rises was revealed. Elevation periodicity persisted, despite the reduction of morbidity level. The mean duration of the whole cycle constituted 12 years. The period of increasing morbidity from minimal to maximal in each cycle constituted 4 years, and of the declination period--8 years. Formalized empirical series of the number of patients and of the morbidity level deviated from 1908 to 1956 not more than by 1 year from the formalized basic curve. Cyclic changes of typhoid-paratyphoid infections morbidity should be taken into consideration in determining the efficacy of prophylatic measures, particularly of mass vaccination.