Six and nine months after the experimental occlusal traumatism, the following histopathological changes of periodontal tissues were observed: --Disorganisation and necrosis of the collagen fibers, abundant cellular infiltration and dilatation of the blood vasels of the periodontium; --The periodontal space was enlarged. Directions of principal collagen fibers was changed. This was especially visible in the region of transeptal fibers; --The observed periodontal changes were correlated with the duration of inflammation and occlusal trauma. The longer these factors persisted the more extensive these periodontal changes occurred.