Pyrost is recently used as a substitute for bone defect in cases where autogenous bone graft is not sufficient. Pyrost is an almost purely deproteinized cancellous bone, processed mainly from calves, and hydroxyapatite constitutes more than 90%. Authors reviewed 40 cases where bone defects after excision or curettage of benign bony lesion were filled with either autogenous bone graft or Pyrost. 22 cases (Group I ) were filled with autogenous bone graft and 18 cases (Group II ) with Pyrost. The mean follow-up was 27 months. The results were as follows;1. The consolidation rates were 96% (21 of 22 cases) in Group I and 95% (17 of 18 cases) in Group II respectively. The consolidation periods were from 2 months to 12 months (mean; 7 months) in Group I and from 3 months to 15 months (mean; 10 months) in Group II respectively. 2. There were complications such as pain, recurrence, and resorption etc. Pain was developed predominantly in patients with Pyrost graft (5 of 18 cases;28%). In autogenous bone graft, pain was developed only in 2 of 22 cases(9%). Regarding othere complications, there was no significant difference between two groups.