Actinomycotic lesions in tissues from a consecutive series of forty-four oxen slaughtered in this country have been examined and compared with fifty specimens imported chiefly from Argentina.The British cases can be divided into two groups, according as the specific granules do not or do contain Gram-staining organisms.The first group, characterised by the presence of granules consisting of clubs without Gram-staining organisms, contains 40 cases. In these the lesions were situated in the cheek, palate, tongue, or lymphatic glands in relation to the mouth and pharynx. From twenty-three of the forty cases, cultures of a non-Gram-staining organism were obtained, which were identical in their characters on nutrient agar plates and in shake glucose agar tubes; and five of the strains were found identical when tested on a large series of differential media. One of the cultures was inoculated into a calf, and produced a local lesion with the characters of a natural lesion.This first group shows complete identity in the histological features and in the anatomical distribution of the disease with Actinobacillosis described by Lignières and Spitz in Argentina. The bacillus obtained has the characters of the Actinobacillus, except that the production of typical granules in the peritoneal cavity of guinea-pigs, described by Lignières and Spitz, has not been demonstrated.All the imported specimens which were examined microscopically exhibited the characters of the lesions of this first group, but the causal organism was not obtained in pure culture.The second group contains the remaining four British cases. The specific granules were composed of clubs and Gram-staining organisms, including branching filaments. The lesions were situated in each case in the inferior maxilla. The investigation of the biological characters of the organisms concerned is still in progress.These results show that Actinobacillosis is widespread in the world, and forms a considerable proportion of the cases of disease in oxen known under the name of Actinomycosis.