On incubation of rabbit polymorphonuclear leukocytes with the S component of staphylococcal leukocidin at 37 degrees C, the 3H-labeled methyl group of S-adenosyl[methyl-3H]methionine was rapidly incorporated into phospholipid. Subsequently, the methylated phosphatidylcholine was degraded by activated phospholipase A2. Complete blockage of the methylation of phospholipid by a mixture of erythro-9-[2-hydroxy-3-nonyl]adenine, adenosine, and L-homocysteine thiolactone markedly inhibited the activation of phospholipase A2 by the S component. It also inhibited the binding of 125I-labeled F component to the cells, but not that of the labeled S component. These results suggest that methylation of phospholipid in the cell membranes by the S component results in activation of phospholipase A2, which induces the binding of the F component to the cells.