Expression levels of adhesion molecules on neutrophils are affected under various conditions, including ischemia, possibly because of associated increases in cell volume. We examined the effects of cell swelling in hypotonic media on the level of L-selectin (CD62L) and ₂-integrin (CD18) on human neutrophils. In hypotonic media, neutrophils shed L-selectin. The shedding was greatly reduced by 30 µM RO31-9790, the metalloprotease (sheddase) inhibitor. Hypotonicity-induced L-selectin shedding was also time and tonicity dependent. Decreasing tonicity caused increased shedding. In 0.6× medium (0.6× the normal tonicity of 300 mosmol/kgH₂O), shedding increased over a 2-h period, after which >70% of the neutrophils had lost L-selectin. In contrast to L-selectin, the level of ₂-integrin on the neutrophil surface was not significantly affected. Thus L-selectin shedding, which occurs on neutrophil activation and is usually accompanied by ₂-integrin upregulation, was selectively induced by hypotonicity without a corresponding effect on ₂-integrin.