A 6-year-old male mongrel dog with a 7-month history of ulnar-radial nonunion fracture was treated with implantation of recombinant human bone morphogenetic protein-2 (rhBMP-2). The dog had received surgical correction three times prior to the admission but radiography of the affected limb revealed a typical figure of nonunion fracture. Glossly, the fractured ends were sclerotic and the area between the ends was filled with fibrous tissue. After debridement the shaft was fixed by an 10-hole plate. rhBMP-2 at a total dose of 256 micrograms was implanted with a synthetic carrier into the 10-mm defect formed by the debridement. Callus formation responding to rhBMP-2 was radiographically observed at 4 weeks after implantation and the defect bridged both fracture ends by 8 weeks after implantation. The plate was removed at 12 months after implantation. Any complications were not observed for 5 months after removal of the plate.