PDGF is a major constituent of platelet rich plasma (PRP), responsible of chemotactic and possibly of mitogenic effects of PRP on osteoblasts. PDGF family includes 5 isoforms: PDGF-AA, PDGF-AB, PDGF-BB, PDGF-CC and PDGF-DD, all expressed in platelets except PDGF-DD. Aim of this study was to analyze the effect of recombinant hPDGF-A, -AB, -B and -C, on migration and proliferation of a human osteoblastic cell line, SaOS-2. Preliminary observations on cell migration were also done in primary cultures of human osteoblasts. In vitro microchemotaxis and 3H-thymidine mitogenic assays were used. While PDGF-AB is active at concentrations present in PRP, PDGF-AA and BB are chemotactic only at much higher doses. PDGF-C is totally inactive alone or together with the active isoforms. PDGF-AA, PDGF-BB and PDGF-C stimulate SaOS-2 proliferation only at the highest dose tested, while PDGF-AB is ineffective. Primary osteoblasts are less sensitive than SaOS-2 and progressively lose responsiveness with increasing passages in culture, in line with loss of cell differentiation. The different PDGF isoforms act differentially on osteoblasts, the-AB isoform appearing the major responsible of the PRP chemiotaxis. PDGF, at the concentrations present in PRP, does not affect cell proliferation.