The nanomechanical properties of single human immunoglobulin G and M antibodies were measured in a liquid environment using a fast force-volume technique with sub-10-nm spatial resolution. The ultrastructural details of these molecules were resolved in the images. Simultaneously, important physical properties, including elasticity, adhesion, and deformation were measured. The dimensions and adsorption of the immunoglobulin M antibodies onto the substrate indicated that they are highly flexible. The antibodies were characterized by a low elastic stiffness (34 ± 10 MPa) and high deformability (1.5 ± 0.5 nm).