The effect of different mandibular postures on the growth of the mandible was studied. A total of 60 female Wistar rats were divided into 3 groups, and all the animals were anesthetized for 6 h daily from the age of 30 days onwards. The first group served as controls. The second had the mandible maintained in a protracted position, and the third had the mandible in an open position during the anesthesia. Macroscopic measurements showed the growth of the mandibular condyle to be increased in a posteroinferior direction and also in a superior direction in the animals with the mandible in an open position. The cartilage layer containing collagen type II was significantly thinned, whereas cell proliferation had significantly increased in the posterosuperior region. In association with mandibular protrusion the thickness of the cell layer containing collagen type II had increased, and cell proliferation in the posterosuperior region had significantly decreased. Significant differences in the growth of the condylar process were observed histologically and histochemically between the experimental animals, implying that the most rewarding aspect of the regulation of condylar growth seems to be the possibility to regulate the maturation rate of the cartilage cells.