BACKGROUND Atomic force microscopy (AFM) can be used to visualize the cell morphology in an aqueous environment and in real time. It also allows the investigation of mechanical properties such as cell compliance as a function of cell attachment. This study characterized and evaluated osteoblast adhesion by AFM. METHODS Human bone marrow stromal cells were cultured on two types of surface to induce weak and strong cellular adhesions. RESULTS Cells were considered as spreading if they had a flattened and lengthened shape and a cytoskeletal organization in the submembrane cytosolic region. Cell detachment demonstrated different adhesion states between adherent cells to be distinguished. The stability of the cytoskeletal fibers indicated that cells were adherent. The elastic modulus was estimated by two complementary approaches. The values deduced were between 3 x 10(2) and 2 x 10(5) Nm(-2) according to the state of cell adhesion and the approaches used to measure this elastic modulus. CONCLUSIONS Although the results were qualitative, a relation may be deduced between the elasticity of living cells as demonstrated by cytoskeletal organization and the state of cell adhesion. The technique could be used to determine the adhesion state of an adherent osteoblast observed under AFM.