Seventy cases of morphologically developed cases or brucellosis in hares are described. Twenty-five of the cases were tested by the cultivation methods and the causative agent was identified as Brucella suis. In females the authors found 57 cases, in males 13 cases. Brucellosis of hares was characterized by a chronical course, by a conspicuous local progression, and by a predominance of pathological changes in the reproductive organs of both sexes. Males showed changes mainly on testes. Nodal, solitary as well as multiple lesions in the parametrium near the uterine wall were particularly typical of females. The hematogenous propagation of brucellosis affected mostly liver and spleen, frequently showing conspicuously large nodes with irregular sides resulting from the growh of the deposits through apposition. The microscopic basis of the changes due to brucellosis was represented by granulomas of histiocytic character with a conspicuously small pyogenic component penetrated by necrosis of a caseous character, rich in lipoids. In comparison with tuberculosis, the brucellosis inflammation in hares shows a conspicuous cellular and nuclear variability in the histiocytic layer of granulomas, prevalent caryloytic disintegration of cellular elements, frequent finding of eosinophiles, and non-constant occurrence of giant multinuclear elements of Langhans cell type.