Twenty-five patients with advanced periodontal destruction were used in the study. Following initial therapy, two angular interproximal defects were selected in each patient. During flap surgery a porous hydroxylapatite implant shaped to fit the periodontal defect was placed in one defect, the other defect was used as nonimplanted control. The material used for implantation was a hydroxylapatite replicate of coral from the genus Porites, with a pore size of 190 to 220 micron. Clinical parameters were measured prior to flap surgery for each of the defects. An occlusal acrylic stent was used to give a stable reference point for pocket depth, attachment level and gingival margin height measurements. Also gingival fluid, gingival inflammation, plaque index and tooth mobility were recorded. Periapical radiographs using a standardized positioning device were also taken. At the time of surgery, the depth of the osseous defect and the height of the alveolar crest were recorded. After 6 months the clinical measurements were repeated and a re-entry surgery was carried out in 15 selected sites. Results showed that the porous implant produced statistically significant reduction in pocket depth, in the depth of osseous lesion, and a statistically significant gain in attachment level, as compared to control areas.