Using 3H-thymidine-labeled MC3T3-E1 osteoblastic cells, the number of osteoblasts bound to titanium surfaces after various surface treatments and incubation periods was directly measured. MC3T3-E1 cell binding to titanium surfaces was saturable at a low level (approximately 10,000 cells/cm2). Although treatment of these surfaces with fibronectin, keratin sulfate, and the fibronectin-derived peptide GRGDS (glycine-arginine-glycine-glutamate-serine) increases cellular binding by 29% to 31%, the relative binding to titanium was 5 to 10 times lower than binding to collagen I gels. A collagen I matrix competed with the commercially pure titanium surfaces for cell binding from solution, suggesting that direct binding of osteoblasts to titanium surfaces present within an organic matrix may not be favored. The significance of immediate and direct bone cell attachment to titanium surfaces for osseointegration should be reevaluated. Schlagwörter: cell attachment, osseointegration, titanium