The purpose of this investigation was to determine the possibility of clinical use of toothash-plaster block implant material with ratio of 2 : 1 by weight. We made 1cm diameter round partial thickness defect at both sides of calvaria. Right side was implanted with block and left side was not implanted as a control site. The following results were obtained : 1. In gross examinations, the implanted site had a hardness on palpation and the margin with host bone was not identified clearly at 12 weeks after operation. But control site contained the fibrous tissue. 2. In the light microscopic examinations, most of the implanted sites were repaired by newly-formed bone at 12 weeks postoperatively. 3. At 8 weeks postoperatively, the implanted particles were divided into small granules and the amount was decreased gradually. Some remained particles were united directly with newly-formed bone. But the implanted particles still remained partly at 24 weeks postoperatively.