We have used the atomic force microscope (AFM) as a tool for testing the biocompatibility of implant materials by investigating the adhesion behavior of osteoblast cells in vitro. This technique allowed the investigation of cytomorphology and cytomechanical properties of living cells on a submicrometer scale. Cell adhesion was investigated on Cobalt-Chromium (CoCr), Titanium (Ti) and Titanium-Vanadium (TiV) substrates, which are of great interest in the field of implant research. The elastic properties and the morphology of living osteoblasts on the metallic substrates were compared with those of osteoblasts cultured on glass and tissue culture polystyrene (PS). Furthermore, a characterization of the surface roughness of the substrates was performed and the surface coverage of proteins after incubation with cell culture medium on the substrates was observed with the AFM.