Ankylosis is a serious condition for the affected teeth as such teeth form part of the remodelling process of the alveolar bone and are therefore progressively resorbed. There are, however, very few clinical studies on tooth ankylosis and the reason for this may be due to the difficulties that are encountered in the diagnosis of minor areas of ankylosis. In the present study, the radiographs, percussion sound and mobility of experimentally extracted and replanted monkey incisors were compared with a morphometric histological study of ankylosis. Ankylotic areas were evident radiographically when the ankylosis was located on the proximal surfaces of the root, but were not evident when the ankylosis occurred on the lingual and labial surfaces. The percussion sound was dull and the mobility normal in all non-ankylotic teeth as well as in those teeth which histologically demonstrated ankylosis on less than 10% of the root surface. When the ankylosis affected 10-20% of the root surface, 2 out of 4 teeth changed their percussion sound from dull to high and these teeth no longer possessed normal mobility. When more than 20% of the root surface was affected with ankylosis, the percussion sound was characteristically high in all teeth and no mobility was present.