Migration of cells in higher organisms is mediated by adhesion receptors, such as integrins, that link the cell to extracellular-matrix ligands, transmitting forces and signals necessary for locomotion(1-4). Whether cells will migrate or not on a given substratum, and also their speed, depends on several variables related to integrin-ligand interactions, including ligand levels(5,6), integrin levels(7-9), and integrin-ligand binding affinities(10-12). These and other(13) factors affect the way molecular systems integrate to effect and regulate cell migration. Here we show that changes in cell migration speed resulting from three separate variables-substratum ligand level, cell integrin expression level, and integrin-ligand binding affinity-are all quantitatively predictable through the changes they cause in a single unifying parameter : short-term cell-substratum adhesion strength. This finding is consistent with predictions of a mathematical model for cell migration(14). The ligand concentration promoting maximum migration speed decreases reciprocally as integrin expression increases. Increases in integrin-ligand affinity similarly result in maximal migration at reciprocally lower ligand concentrations. The maximum speed attainable, however, remains unchanged as ligand concentration, integrin expression, or integrin-ligand affinity vary, suggesting that integrin coupling with intracellular motors remains unaltered.