A sequence of research on "Cara inchada", a periodontal disease of young cattle (CI), involving heavy losses in Brazil, is described and results of laboratory investigations and field experiments are reported. A suspicion of being a primary nutritional disease of the skeleton could not be confirmed. In the other hand, bacteria, especially of the genus Bacteroides, were isolated from the periodontal CI-lesions. These bacteria possess enough pathogenic potential, through the production of enzymes and endotoxins, to cause primary destruction of the periodontal tissues. The lesions of the upper jaw, and also of the mandibula, of the diseased animals were diagnosed as a purulent periodontitis and a secondary ossifying alveolar periostitis. As CI occurs enzootically on new, cultivated pastures in cleared forest and savanna areas, and as the incidence of the disease declines with the years of pasture use, in order to disappear again, it can be postulated that a determining factor exists in the soil and consequently in the pasture, the disturbance of the equilibrium of the microflora in the formerly virgin soil possibly causes a modification of the flora of the rumen and the oral cavity, so that bacteria, as Bacteroides spp., present in the subgingival space, could dominate and become pathogenic. The frequent diarrhoea observed in calves affected by CI could be a consequence of the modification of the microflora in the digestive tract. Accordingly, CI could be considered as an infectious periodontitis of calves due to altered ecological soil conditions.