We have combined the tapping-mode atomic force microscope (AFM) and quartz crystal microbalance (QCM) for simultaneous investigation and characterization of protein adsorption on various metallic surfaces using these two instruments. The adsorption of proteins such as human plasma fibrinogen and anti-human immunoglobulin onto the metal or oxide/QCM surface were monitored using both methods at the same time when varying the concentration of proteins. The combination of AFM with QCM allowing the simultaneous measurements with two techniques working at very different scales and probing different properties of the adsorbed layer provides quantitative and qualitative information that can distinguish different protein adsorption behavior. (C) 2003 American Vacuum Society.