The purpose of this study was to investigate the effectiveness of a synthetic nonporous hydroxyapatite graft material (OrthoMatrix HA-500), a porous replamineform hydroxyapatite graft material (Interpore 200), and a debrided control with respect to defect fill. Twelve adult patients having periodontitis and three similar angular osseous defects as verified by radiographic analysis and clinical probe depths greater than or equal to 5 mm were selected. Clinical parameters gathered prior to surgical intervention and at identified postoperative visits included plaque index, probing depth, and standardized radiographic examination. Customized acrylic stents were used as fixed reference guides for the insertion of endodontic silver points to the base of each defect during both initial and 6-month reentry surgeries. A total of 36 defects were randomly assigned to one of three treatment modalities such that 12 defects received OrthoMatrix HA-500, 12 received Interpore 200, and 12 served as debrided controls. Comparison of nonporous hydroxyapatite, porous replamineform hydroxyapatite, and debrided control treatment modalities revealed a statistically significant improvement (P less than 0.05) in the mean per cent of defect resolved in only those sites treated with nonporous hydroxyapatite. Similar positive trends were seen in the sites treated with nonporous hydroxyapatite for mean reentry defect depth and mean defect fill although these were not statistically significant (P greater than 0.05). No other significant differences were noted.