Tricalcium phosphate (TCP) is a porous ceramic which has biological properties of being non-reactive and resorbable, and acts as a scaffolding for bone ingrowth, undergoing progressive degradation and replacement by bone. Tricalcium phosphate has been shown to be comparable to autogenous bone graft in small periodontal defects. However, orthopedic defects are much larger. This prompted us to review the bone ingrowth potential in large cancellous bone defects (up to 12 cm3) in adult pigs. To quantitate bone ingrowth potential, three skeletally mature pigs had metaphyseal defects created in the tibia and femur of each hind limb, for 12 total sites. Twelve-cc defects in the distal femur and eight cc defects in the proximal tibia were made. Bone curetted was saved to be used as autogenous graft in the control, while the other ipsilateral defect was packed with tricalcium phosphate. Four months following the initial defect, the opposite hind extremity was similarly operated. All animals were sacrificed at nine months. Specimens were imbedded in methyl-methacrylate, cut at 120 microns, and stained. The quantity of regenerated bone was measured by histomorphometric techniques. Qualitative assessment at four months revealed absence of inflammation and TCP surrounded by trabecular bone, which was uniformly viable. There was very little TCP left by nine months. Quantitative analysis revealed the tibias to have a higher percent net bone replacement with TCP as compared to the control (32 percent versus 13 percent). The femoral TCP-filled defects were comparable to autogenous bone (both measured 29 percent).(ABSTRACT TRUNCATED AT 250 WORDS)