Recently, AFM-based force spectroscopy has been used to quantify single-molecule adhesion forces on living ameboid cells. Force spectroscopy was used to measure the rupture forces of single receptor-ligand bonds which can occur rapidly between the cell types used, a metastasising B16 melanoma cell and a vascular bEnd.3 endothelial cell. Parameters which influence the critical experimental conditions are discussed to discriminate between multiple bond ruptures and single bonds. Under physiological conditions of temperature and pH the force measurements show an average rupture force of 33 pN (SD = 12 pN) for single bonds. Single-molecule force spectroscopy will be very useful to study the regulation of cell adhesion on a molecular level in normal processes, such as leukocyte homing, and in major human disorders, including tumor metastasis, autoimmune diseases and atherosclerosis.