STUDY DESIGN: A comparative in vivo study between ceramics with different compositions. OBJECTIVES: To compare the biodegradation and osteoconduction properties of CaO-SiO2- P2O5- B2O3 glass-ceramics and Cerabone(R)-AW. Summary of Literature Review: Bioglass ceramics can be used as bone graft substitutes. However, no study has been undertaken to investigate the possibility of CaO-S i O2-P2O5-B2O3 glass-ceramics as a bone graft substitute. MATERIALS AND METHODS: Porous CSPB2 implants (44.07% CaO, 40.28% SiO2, 8.1% P2O5 and 5.0% B2O3), porous CSPB3 implants (43.76% CaO, 43.41% SiO2, 4.05% P2O5 and 7.5% B2O3) and porous Cerabone(R)-AW were prepared by the polymer sponge method. Single-level posterolateral spinal fusions were performed on sixty New Zealand white male rabbits. The animals were divided into four groups (9 of autograft, 17 per 3 kind of porous implant group) according to the implant material used: autograft, CSPB2, CSPB3 and Cerabone(R)-AW. Radiographs were performed every two weeks. All animals were sacrificed 12 weeks after surgery. Manual palpation and uniaxial tensile strength were determined. The proportion of the area occupied by the ceramics in the final compared to the initial radiographs was calculated. Decalcified and undecalcified histological sections were evaluated by light microscopy. RESULTS: Fifty one rabbits were evaluated. The union rates were 100 (9 out of 9), 80 (8 out of 8), 81.1 (9 out of 11) and 90.9% (10 out of 11) in the autograft, Cerabone(R)-AW, CSPB2 and CSPB3 groups, respectively. The proportion of the area occupied by Cerabone(R)-AW (90.8 % +/- 14.0) was significantly higher than for CSPB2 (73.1% +/- 11.5) and CSPB3 (73.5% +/- 10.0)(p=0.0011). The mean values of the tensile strengths of Cerabone(R)-AW (214. +/- 57.3N), CSPB2 (214. +/- 57.3 N) and CSPB3 (217 +/- 70.1 N) were not significantly different (p>0.05). CONCLUSION: CSPB2 and CSPB3 had similar tensile strengths and fusion rates of the fusion masses as those of Cerabone(R)-AW; however, they degraded more rapidly than Cerabone(R)-AW. These findings suggest that CSPB2 and CSPB3 grafts can be used as a more ideal new bone graft substitutes than Cerabone(R)-AW.