A five-year ecological study of the largest tularemia natural focus in Croatia (Yugoslavia) has revealed that the focus is of a meadow-field type and that the common vole is the crucial member of the local tularemia pathobiocenosis. The occurrence of epizootics and of concomitant epidemics is associated with the bionomy of the latter which, in its turn, is strongly influenced by environmental factors. It was possible therefore to link tularemia outbreaks with special meteorological and hydrological conditions, i.e. with warm and dry spring-summer seasons and the Sava river floods. The proper understanding of the underlying ecological laws furnishes a sound basis for the forecasts of future epidemiological events.