OBJECTIVE: To determine whether culture expanded bone marrow derived mesenchymal stem cells (MSCs) in combination with beta-tricalcium phosphate(beta-TCP) can repair critical cranial defects in New Zealand rabbits. METHODS: In group A(n = 20), MSCs from homogeneous rabbits were isolated and expanded in vitro and then implanted onto the pre-molded porous beta-TCP. The MSCs-beta-TCP complexes were implanted into rabbit critical cranial defects. In group B (n = 10), The defects were repaired with beta-TCP only. In group C(n = 4), the defects were left un-repaired. Samples were extracted 6 and 12 weeks after operation for histological, histochemical and immunohistochemical analysis. RESULTS: In group A, bone-like tissue formation could be seen on the surface of the implants. Microscopic analysis demonstrated certain degradation of beta-TCP and extensive new bone filling in rich extracellular matrix after 6 weeks. The cells were stained positively for type I collagen. After 12 weeks, the bioceramics had almost completely degraded and abundant bone formation could be seen in the whole defects. In group B, marginal bone ingrowth was observed after 6 weeks and the number of osteoblasts increased significantly after 12 weeks. However, no new bone formation could be detected in the middle of the material. In group C, only a small quantity of new bone formation was found along the margin of defects. CONCLUSION: Transplantation of MSCs with beta-TCP can serve as an example of a cell-based treatment for bone regeneration in skeletal defects.