Tissue samples from three subjects who had periodontal defects treated with a porous hydroxylapatite implant were investigated using light microscopy and scanning electron microscopy. The 3-month specimen showed connective tissue infiltration through the pores and a narrow zone of bone formation present along the walls of the pores. At 4 months, continued evidence of bone deposition was present with osteocytes, osteoblasts and organization of collagen fibers apparent throughout the implant. The 6-month implant had further evidence of continued bone formation with lamellar bone being the major component within the pores.