Many researches have concentrated recently on the resorbable implant materials, for the implant materials have a difficulty in the physiological and structual affinity around the surrounding tissues. The main purpose of biodegradable ceramic is to fill a space as well as to eliminate the need for a metallic implant. This material would not only provide a matrix for bone formation but, by concurrent resorption or degradation, would disappear from the site of implantation. The basic composition of biodegradable ceramic is calcium phosphate and the representative material is tricalcium phosphate. The author investigated this material using rabbits and dogs far clarifying the correct mechanism of the biodegradation, and further information of new bone formation. On the basis of this I have studied to find possibility of development about ideal alloplastic materials. Bony defects, 0.5cm size, were created in the femur of rabbits and the granule type, tricalcium phosphate, Ca3(P04)2, Synthograft, Miter Inc., was implanted for investigating the tissue reaction through 12 weeks, and another experiment was performed in the dogs in the same manner as the rabbits, except bony defects, 2cm size for studing the degree of the new bone formation during the 6 weeks. The results were examined with light microscope for histologic appearances with conventional stainable specimen, and microradiographic examination was performed with undecalcified specimen for the degree of calcification and stage of osteon maturation. The results were as follows, l. In both rabbits and dogs, tricalcium phosphate did not induce the abnormal tissue reaction and the wounds were healed normally. 2. Tricalcium phosphate particles began to have affinity with surrounding tissues from the 1st week and the fibrous invasi0e. was represented directly to the particle surface. 3. Replacement of tricalcium phosphate was represented with the disappear of it concurrently and this material developed the matrix for new bone Formation and was ossified directly. 4. The matrix for the new bone formation is resemble to acellular osteoid and the calcified trabecular bone was replaced. 5. In the disappear of this material, were not related the specific giant cells and macrophages. 6. In microradiogram, the calcification of new bone revealed a similar density with the radiopaque tricalcium phosphate from the 3rd weed, with time the formation and maturity of the new bone were manifested more distinctly than the control group. 7. The radiodensity of tricalcium phosphate particles has not specific change through the experiment period. 8. The small amount of tricalcium phosphate particles was remained at the implant site of bone marrow even at 12 weeks.