To investigate the effects of 1α-OH-D₃ (ALFAROL) on the condylar cartilage of mouse mandibles, 3-day-old mice (ddY) were used in this experiment. 1α-OH-D₃ increased serum Ca level and decreased condylar cartilage. With administration of 1α-OH-D₃ it was difficult to distinguish the proliferating zone from mature cell zone in condylar cartilage by morphology.

Furthermore, the cells in proliferating and maturecell zones were electron microscopically exposed to morphological changes compared with the control. The labeling indexes of ³H-thymidine on the cells in proliferating and mature cell zones were reduced by one-third of control level. Moreover, the positive reaction was stained with alcian blue and PAS reduced with the administration of 1α-OH-D_3. From the above results, it is suggested that 1α-OH-D₃ inhibited the proliferation and glycosaminoglycan synthesis of condylar chondrocytes.