Localization and expression of connective tissue growth factor/hypertrophic chondrocyte-specific gene product 24 (CTGF/Hcs24) during fracture healing in mouse ribs were investigated. In situ hybridization demonstrated that CTGF/Hcs24 mRNA was remarkably expressed, especially in hypertrophic chondrocytes and proliferating chondrocytes, in the regions of regenerating cartilage on days 8 and 14 after fracture. CTGF/Hcs24 mRNA was also expressed in proliferating periosteal cells in the vicinity of the fracture sites on days 2 and 8, and in cells in fibrous tissue around the callus on day 8. Northern blot analysis showed that expression of CTGF/Hcs24 mRNA was 3.9 times higher on day 2 of fracture healing than that on day 0. On day 8, it reached a peak of 8.6 times higher than that on day 0. It then declined to a lower level. Immunostaining showed that CTGF/Hcs24 was localized in hypertrophic chondrocytes and proliferating chondrocytes in the regions of regenerating cartilage, and in active osteoblasts in the regions of intramembranous ossification. Although CTGF/Hcs24 was abundant in the proliferating and differentiating cells (on days 8 and 14), immunostaining decreased as the cells differentiated to form bone (on day 20). CTGF/Hcs24 was also detected in cells in fibrous tissue, vascular endothelial cells in the callus, and periosteal cells around the fracture sites. These results suggest that CTGF/Hcs24 plays some role in fracture healing.