Various alloplastic materials have been used on the periodontally diseased ossous defects. Hydroxyapatite, which is used the most common alloplastic material is a non-resorbable form of calcium phosphate and natural coral which is a biodegradable by carbonic anhydrase in osteoclast was introduced recently. The purpose of the present study was to evaluate the clinical effects of porous hydoxyapatite and natural coral on the human periodontal defects. Four males and three females who had adult periodontitis were selected for this study. The teeth that had similar bone loss radiographically and periodontal pocket deeper than 5mm were selected. Gingival recession, pocket depth, plaque index(Silness & Loe), sulcus bleeding index and tooth mobility (measured by Periotest$^{(r)}$) were examined before graft. Before insertion of alloplastic materials, the depth from CEJ to bone crest and from CEJ to base of the osseous defect was recorded. Porous particulate hydroxyapatite(Interpore 200$^{(r)}$, A group) was place on the defect and natural coral(Biocoral$^{(r)}$, B group) was placed on the defect of the opposing tooth. Six months post-surgically the same parameters were recorded by reentry procedures. A and B group showed 0.6mm of mean recession. Mean reduction of pocket depth were 5mm for A group and 4.9mm of B group. Reduced SBI and tooth mobility were recorded. Osseous defect fills of the original defects were 2.9mm for A and 3mm for B group. Percentage defect fills were 71% for A and 59% for B group. The difference of defect fill between pre- and post-insertion was statstically significant(p<0.05). But the difference between the two groups was not significant statistically(p<0.05). The clinical impression at 6 month re-entry and the numerical date indicate that natural coral as well as porous particulate hydoxyapatite has a definite potential as an alloplastic implant in the treatment of periodontal osseous defects.