The trends and main factors influencing the fluctuations of the levels of tularemia and pseudotuberculosis morbidity in the Iaroslavl region were revealed by the methods of mathematical statistics (regress analysis, time-series analysis, etc.). Tularemia morbidity was 0.467 +/- 0.216 cases (1950-1997) and pseudotuberculosis morbidity was 0.979 +/- 0.297 cases (1979-1997) per 100,000 of the population. The multiple regression equations permitting the prognostication of tularemia and pseudotuberculosis morbidity in the Iaroslvl region were derived.