The influence of titanium surface properties on in vitro adsorption isotherms of fibronectin, promotion of Staphylococcus aureus adhesion, and binding of a monoclonal antibody to the cell-binding domain of fibronectin was examined. Treatments producing different surface roughness were applied to a single side of commercially pure titanium coverslips, which was either mechanically polished (P), or polished and then acid attacked with H2SO4/HCl (PA), or sandblasted and then acid attacked (SLA), whereas the untreated side was blocked by an albumin coating layer. Incubation of the coverslips with concentrations of soluble 3H-labelled fibronectin increasing from 1 to 16 micrograms/ml led to the saturation of all surfaces with immobilized protein from 4 to 16 micrograms/ml. Promotion of S. aureus adhesion by fibronectin adsorbed on all surfaces and binding of the monoclonal antibody to its cell-binding domain was to some extent proportional to the amount of immobilized protein but also showed some minor differences between surfaces. More important material-related differences were observed when fibronectin adsorption isotherms were expressed as a function of the effective, roughness-corrected surface area, yielding amounts of immobilized fibronectin on the rough PA and SLA titanium surfaces which were 50% lower than those adsorbed on either smooth P or polymethylmethacrylate coverslips used as controls. In conclusion, surface treatments increasing the surface roughness of titanium do not increase, but may partly decrease in vitro adsorption of fibronectin. Despite adsorbing different amounts of fibronectin, both rough and smooth titanium surfaces promote normal expression of 2 major functional domains of this protein.