It is well accepted that reduced masticatory function resulted from a soft diet with low physical consistency causes morphologic and histologic alterations in the craniofacial skeleton in growing animals. It is also assumed that these alterations are associated with reduced proliferative activity of osteoblasts on the bone surface, indicating a significant role of mechanical stimuli mediated by various local growth factors such as insulin-like growth factor-I (IGF-I) and parathyroid hormone (PTH). A previous study demonstrated that PTH accelerated the effect of IGF-I on bone formation. This study was thus conducted to examine the effect of PTH on the induction of osteoclasts and osteoblasts and the subsequent nasopremaxillary growth under different mechanical loading conditions from mastication. In animals treated with PTH, the nasal bone length increased significantly in the solid-diet group. No significant differences in these dimensions were found between the solid-diet mice injected with physiological saline and the granulated-diet group injected with PTH. It is shown that PTH induces nasal and premaxillary growth, and the effects may be exerted if mechanical loading from mastication is sufficient. It is also demonstrated that the effects of PTH are more potent in the osteogenic activity than in the osteoclastic one, in terms of more significant expression of osteoblasts than osteoclasts.