The articular disk has been implicated as a controlling factor of the form of the condylar head. In a study investigating the role of articular function on the condylar cartilage, 35 adult Wistar rats (mean weight 327 g) were operated on to establish the effects of loss of the dkisk and capsule on the form of the condylar head. These animals had their zygomatic arch and disk removed on one side, while a neutral procedure was performed on the opposite side to act as a control. The results showed extremely unusual shapes to the form of the condylar head and implicated the disk as the controlling factor. Studies with tritiated thymidine also showed an increase in proliferative activity.