&NA;Studies concerning natural and synthetic graft materials that have been used in different medical procedures have focused on freezedried bone, coral, hydroxylapatite, and tricalcium phosphate. This study histologically investigates the effects of these materials on the healing of bone defects. The experiments were performed on 30 albino rabbits. Cavities were drilled in the posterior right tibias of rabbits and were filled with coral, freeze‐dried bone, hydroxylapatite, or calcium hydroxide. One cavity was left unfilled as a control. The bone in which the materials were implanted was excised at 7, 15, 30, 45, and 60 days. After the histological staining procedures, the prepared materials were observed using a light microscope. Although all materials showed good bone remodeling at the end of 60 days, coral and hydroxylapatite materials could be seen in the bone structure. The most effective materials within bone defect improvement were freeze‐dried bone and calcium hydroxide. (Implant Dent 2000;9: 226‐235)