The ultimate goal of periodontal treatment has been to facilitate regeneration of diseased periodontal tissues, destroyed by inflammatory periodontal disease. Various implant materials have been used to restore the alveolar bone defects. Of the various materials, porous replamineform hydroxyapatite (PHA) has good biocompatibility when placed in a bone tissue, and maintains alveolar ridge for a long period. Decalcified freeze dried bone(DFDB) has been widely used in alveolar bone defects because of its conformity and high osteogenic potential. The purpose of this study was to evaluate the effects of PHA and DFDB on the regeneration of the alveolar bone between fresh extraction sockets and periodontally involved extraction sockets. Experimental periodontitis was induced by the ligation of orthodontic elastic threads after surgically creating periodontal defects on the premolars on the right side of 2 adult dogs for 8 weeks. Following the extraction of each tooth, PHA and DFDB were inserted in the extraction sockets. In control group 1, PHA was inserted in the fresh extraction sockets, and in control group 2, DFDB was inserted. In experimental group 1, PHA was inserted in the periodontally involved extraction sockets, and in experimental group 2, DFDB was inserted. After 20 weeks, the specimens were prepared and stained with Hematoxylin-Eosin stain for the light microscopic evaluation. The results of this study were as follows. 1. No inflammation associated with implant materials was evident in any of the groups. 2. DFDB was completely resorbed, PHA was remained in the extraction sockets in the control and experimental groups. 3. In control group 1 and experimental group 1, extraction sockets were not completely filled with new bone. However, original forms of alveolar crests were maintained in control group 2 and experimental group 2. 4. In control group 1 and exprimental group 1, PHA particles surrounded with many giant cells were well tolerated by the fibrous connective tissues in the coronal part of the socket, In the inferior part of the socket, PHA particles were incorporated into the new bone. In both control group 2 and experimental group 2, DFDB was replaced by newly remodeled bone. 5. No differences of degree of new bone formation were evident between control and experimental groups.