Twenty Sprague‐Dawley rats were utilized to study the effects of a distal occlusion on the mandibular joint. The experimental period varied from one to four weeks. Cellular behavior and synthesis of new bone was revealed radioautographically after the injection of tritiated thymidine and tritiated proline respectively. The following structures within the joint were studied: (1) the fibrous layer of the articular fossa, (2) the fibrous and (3) the embryonic zone of the condyle. The number of labeled cells decreased in all areas analyzed after the first week of experiment but by two weeks had increased above the control. At four weeks, while still higher than the control, the radioactive index was decreasing. Of the structures studied, the embryonic layer showed the greatest response in number of cells undergoing DNA synthesis due to: (1) growth, (2) age, and (3) distal displacement of the mandible. Within the fibrous layer of the condyle and articular fossa, however, except for the central portion of the latter, the difference in radioactive index between control and experimental groups was negligible. Concomitant with the downward and forward growth of the mandible the number of cells undergoing DNA synthesis was highest in the posterior portion of the condyle. Initially, resorption was observed in the area of the external pterygoid attachment of the condyle followed by new bone formation as evidenced by tritiated proline. From this investigation the following conclusions were drawn: (1) The cells within the embryonic zone of the condylar cartilage can be stimulated, even in the adult, to increase their rate of cellular division to adapt to changes in mandibular position. (2) The articular fossa and disc remain unaltered following distal mandibular displacement. (3) Tension within the external pterygoid muscle will result in gross morphologic alterations on the anterior border of the condyl