To study the biologic response, three commercial calcium phosphate implant materials (Calcitite, Periograf, Synthograft) were implanted in cuspid root "windows" in four beagle dogs. No implant material was placed in the fourth cuspid window which served as a control. Following mucoperiosteal flap elevation, windows were chiseled in bone to the root surface which allowed implant particles to contact bone, fibrous connective tissue, cementum and dentin without exposure to the oral environment. Animals were sacrificed after 1, 3, 5 and 6 months. Histologically, all implant materials were well tolerated. At 1 month, implant particles were surrounded by fibrous tissue. Fibrous tissues filled the control defect. At 3 months, implant sites exhibited partial bony repair with connective tissue surrounding implant particles. A ring of osteoid surrounded Synthograft particles. Control defect repair was complete. At 5 and 6 months, implant sites exhibited advanced, though incomplete, bony repair. New bone encompassed the Synthograft particles. It was concluded: Control sites healed most rapidly. Calcitite and Periograft were well tolerated space occupiers. Synthograft was a nidus for bone deposition.