The aim of this study was to investigate the effect of platelet-rich plasma (PRP) on the proliferation of osteoblast-like cells in vitro. PRP was prepared using a centrifuge; the number of platelets (n = 32) and the levels of platelet-derived growth factor-AB (PDGF-AB), transforming growth factor-beta1 (TGF-beta1), and insulin-like growth factor-I (IGF-I) were measured (n = 16). For the proliferation assay, SaOS-2 was cultured in the presence of platelet-poor plasma (PPP), whole blood, or PRP. The cell number was counted after 36 and 72 hours. To investigate the effect of each growth factor, the cells were cultured with PRP in the absence or presence of neutralizing antibodies, and counted as described. The mean platelet count of PRP was 1546.36 +/- 382.25 x 10(3)/microL, and the mean levels of PDGF-AB, TGF-beta1 and IGF-I were 0.271 +/- 0.043, 0.190 +/- 0.039, and 0.110 +/- 0.039 ng/1500 x 10(3) platelets, respectively. Cell proliferation was enhanced in all PRP groups in a dose-dependent manner, and all neutralizing antibodies significantly suppressed proliferation compared with the PRP group, lacking antibody, at 36 hours. However, at 72 hours, the neutralizing antibodies of PDGF and TGF-beta1, but not IGF-I, significantly suppressed proliferation. These results show the beneficial abilities of PRP in the proliferation of osteoblast-like cells from the standpoint of growth factors, including the contribution of each factor.