The European brown hare (Lepus europaeus) plays an important role in the ecology of tularemia, and it may serve as a significant source of human infection. The aim of the present study was to examine the lesions induced by Francisella tularensis in 50 cases of naturally infected seropositive European brown hares. Gross pathological examination revealed scant to numerous grayish-white foci with diameters of 0.1 to 1.0 cm in single organs (24 cases) or multiple organs (20 cases) in 44 of 50 cases (88%). These lesions proved to be areas of granulomatous inflammation, frequently encompassing necrosis. F tularensis antigen was detected with immunohistochemistry in 46 of 50 cases (92%), whereas F tularensis ssp holarctica was isolated by culture and identified by polymerase chain reaction from 35 of 50 cases (70%). Infection by the respiratory route is suggested by the presence of the tissue lesions in thoracic organs of 44 of 50 cases (88%). These results emphasize the importance of the European brown hare as a reservoir of tularemia.