Anti‐neutrophil antibodies (CD15) bind to a simple sugar (lactose‐N‐fucopentaose III, LNF III) known to be present on the chains of the adhesion molecules on neutrophils. We have demonstrated that pre‐incubation of neutrophils with a CD15 antibody increases neutrophil adherence to endothelium by a neutrophil‐dependent mechanism. This augmented adhesion can be inhibited by antibodies directed against the α and β chain of the leukocyte function‐associated antigen 1 (LFA‐1) molecule. There is also some increase in surface LFA‐1 expression on neutrophils after CD15 incubation, suggesting that CD15 antibodies increase neutrophil adhesion by an LFA‐1‐dependent mechanism. The increase in LFA‐1 expression after CD15 incubation occurs in the presence of a protein synthesis inhibitor. As LFA‐1 is not stored intracellularly, the increased adherence of the neutrophils, and increased LFA‐1 expression on their surface, suggests the possibility that the CD15 antibodies are binding to the LNF III antigen present on the α and β chains of LFA‐1, producing their effect by activating the molecule, perhaps by exposing new antigen sites by a stearic effect.