The regulation of callus formation during fracture repair involves the coordinate expression of growth factors and their receptors. This article describes the temporal and spatial expression of noggin gene, an antagonist to bone morphogenetic protein (BMP), during the fracture repair process. Noggin expression was examined by means of Northern blotting and in situ hybridization and compared with the expression pattern of BMP-4 in a model of fracture repair in adult mice. Expression levels of noggin messenger RNA (mRNA) were enhanced in the early phase of fracture callus formation. The localization of the noggin mRNA was similar to that of BMP-4 mRNA. Distinct noggin mRNA signals were located predominantly in cells lining the periosteum and the cortical endosteum near the fracture site at 2 days after fracture. At 5, 10, and 21 days after fracture, noggin mRNA was detected in the chondrocytes and osteoblasts in the newly formed callus. The pattern of localization was indistinguishable from that of BMP-4. These results suggest that the noggin/BMP-4 balance could be an important factor in the regulation of callus formation during fracture healing.