The effect of surface roughness of the titanium alloy Ti-6Al-4V (Ti alloy) on the short- and long-term response of human bone marrow cells in vitro and on protein adsorption was investigated. Three different values in a narrow range of surface roughness were used for the substrata (R(alpha): 0.320, 0.490 and 0.874 microm). Cell attachment, cell proliferation and differentiation (alkaline phosphatase specific activity) were determined past various incubation periods. The protein adsorption of bovine serum albumin and fibronectin, from single protein solutions, on rough and smooth Ti alloy surfaces was examined with two methods, X-ray photoelectron spectroscopy (XPS) and radiolabeling. Cell attachment and proliferation were surface roughness sensitive and increased as the roughness of Ti alloy increased. No statistically significant difference was observed in the expression of ALP activity on all three Ti alloy surfaces and culture plastic. Both methods, XPS and protein radiolabeling, showed that human serum albumin was adsorbed preferentially onto the smooth substratum. XPS technique showed that the rough substratum bound a higher amount of total protein (from culture medium supplied with 10% serum) and fibronectin (10-fold) than did the smooth one. The cell attachment may be explained by the differential adsorption of the two proteins onto smooth and rough Ti alloy surfaces.