In this study, the phenotypic expression of osteoblast progenitor cells, 2T9, on characterized titanium surfaces was examined in the rpesence of a bone morphogenetic protein-2 (BMP-2). X-ray photoelectron spectroscopy spectra indicated the presence of titanium dioxide on titanium surfaces, along with surface contaminants such as carbon and nitrogen. In the in vitro study, the activity of BMP-2-treated osteoblast cells on titanium surfaces was mar ked by significantly higher alkaline phosphatase-specific activyt and 1,25 (OH2) vitamin D3-stimulated osteocalcin production when compared to the untreated cells on titanium surfaces.