Integrin α₄β₇ mediates rolling adhesion in Ca²⁺ and Ca²⁺ + Mg²⁺, and firm adhesion in Mg²⁺ and Mn²⁺, mimicking the two key steps in leukocyte accumulation in inflamed vasculature. We mutated an interlinked linear array of three divalent cation-binding sites present in integrin β-subunit I-like domains. The middle, metal ion–dependent adhesion site (MIDAS) is required for both rolling and firm adhesion. One polar site, that adjacent to MIDAS (ADMIDAS), is required for rolling because its mutation results in firm adhesion. The other polar site, the ligand-induced metal binding site (LIMBS), is required for firm adhesion because its mutation results in rolling. The LIMBS mediates the positive regulatory effects of low Ca²⁺ concentrations, whereas the ADMIDAS mediates the negative regulatory effects of higher Ca²⁺ concentrations, which are competed by Mn²⁺. The bipolar sites thus stabilize two alternative phases of adhesion.