The ability of several chemotactic factors to alter polymorphonuclear neutrophil (PMN) adhesiveness to nylon fibers was studied. Partly purified bacterial chemotactic factor, the isolated chemotactic fragment of human C5, and the chemotactic synthetic tripeptide, formyl-methionyl-leucyl-phenylalanine, transiently enhanced the nylon fiber adhesiveness of rabbit peritoneal PMSs. The capacity of these chemotactic factors to augment PMN adherence closely paralleled their ability to aggregate PMNs in suspension and to induce neutropenia when infused into rabbits. However, at least a portion of the adhreence-augmenting capacity of these agents was independent of their ability to induce PMN aggregation. Thus, chemotactic factors appear to transiently enhance PMN adhesiveness to a variety of surfaces. This hyper-adhesiveness may underlie the augmented nylon fiber adherence, aggregation, and neutropenia induced by these factors.