Cross-linking of antibodies bound to CD11b or CD18 on the neutrophil surface produced a large Ca2+ transient (max. approximately 500 nM). The major source for this Ca2+ rise (more than 81%) was from an intracellular Ca2+ store. After integrin cross-linking, the Ca2+ transient induced by N-formyl-methionyl-leucyl-phenylalanine (FMLP) was decreased, suggesting that both stimuli acted on the same Ca2+ store. Release from the Ca2+ store, induced by integrin cross-linking, was visualized as a 'cloud' of elevated Ca2+, which remained localized even in the presence of extracellular Ca2+. The generation of localized cytosolic Ca2+ signals by cross-linking integrin may be important for triggering localized cellular responses.