In order to study the biophysical forces involved in cell-substrate (or cell-cell) adhesion, it is necessary to measure the strength of adhesion. Two questions can be addressed using the centrifugal cell adhesion assay provided in this unit: what is the ligand-receptor affinity for cells adhering at 4 degrees C and what is the strength of the ATP-dependent processes that strengthen adhesion at 37 degrees C. In both cases, the strength of adhesion is measured as the resistance to disruption in the presence of a measured centrifugal force.