['The objective of this study was to compare culture-expanded bone marrow-derived mesenchymal stem cell and PRP loaded to natural bone mineral (Bio-Oss) and beta-TCP for rat calvarial bone repair.', 'Twenty-two adult male Sprague-Dawley rats were randomly divided into 2 groups (n = 11). In the first group, 2 calvarial defects, 5 mm in diameter, were prepared in the parietal bone. The left defect was filled with Bio-Oss plus PRP while the right defect was filled with mesenchymal stem cell cultured on Bio-Oss. Kasios as a bone substitute was replaced in the second group. The animals were humanely killed 6 weeks postsurgery and the amount of the bone regeneration evaluated using histometric analysis.', 'The bone fill length in the calvarial defect had statistically significant difference with other groups (P < .05). In both groups, mesenchymal stem cell revealed a higher percentage of bone formation in comparison with the PRP groups.'] Do mesenchymal stem cells enhance bone regeneration in rat calvarial critical size defects more than platelete-rich plasma?