We examined the mechanism by which lysophosphatidylcholine (LPC) regulates ₂ integrin-mediated adhesion of eosiniophils. Eosinophils were isolated from blood of mildly atopic volunteers by negative immunomagnetic selection. [[beta]_]2-integrin-dependent adhesion of eosinophils to plated BSA was measured by residual eosinophil peroxidase activity. LPC caused maximal adhesion of eosinophils to plated BSA at 4 µM. Lysophosphatidylinositol, which has a similar molecular shape, mimicked the effect of LPC on eosinophil adhesion, while neither lysophosphatidylserine nor lysophosphatidylethanolamine had any effect. Phosphatidylethanolamine, a lipid that has a molecular orientation that is the inverse of LPC, blocked eosinophil adhesion caused by LPC. Unlike platelet-activating factor (PAF), a G-protein coupled receptor agonist, LPC did not cause Ca²⁺-store depletion, but caused increased Ca²⁺ influx upon addition of Ca²⁺ to extracellular medium. This influx was not inhibited by U73122, a phospholipase C inhibitor, demonstrating independence from the G protein-activated phospholipase C pathway. Ca²⁺ influx was inhibited by either preincubation of phosphotidylethanolamine or La³⁺, a broad spectrum blocker of cation channels. LPC induced upregulation of the active conformation of CD11b, which was blocked by preincubation with phosphatidylethanolamine. These data suggest that LPC causes a non-store operated Ca²⁺ influx into eosinophils, which subsequently activates CD11b/CD18 to promote eosinophil adhesion.