A non-union model was established in the mid-part of the radial diaphysis in dogs. The non-union was treated with operative implantation of a carrier (guanidine-extracted, demineralized bovine bone or a polylactic acid polymer), alone or in combination with fractions that had been enriched in bone morphogenetic protein. All sites of treatment were examined radiographically and histomorphometrically at twelve weeks after implantation. Guanidine-extracted, demineralized bovine bone, alone or combined with fifteen milligrams of canine bone morphogenetic protein, failed to induce any healing of the non-union. When polylactic acid alone had been implanted, a small amount of reparative new bone was found in the defect at three months. When polylactic acid combined with fifteen milligrams of canine bone morphogenetic protein had been implanted, a significant increase in new bone formation was seen (p less than 0.03), compared with that seen in control animals. Trabecular bone bridged the gap between the proximal and distal fragments in all four specimens from the dogs that had received that treatment. In contrast, when polylactic acid combined with bovine bone morphogenetic protein had been implanted, significant reparative new bone was not found in the defect at three months.