hFpB causes directed cell migration of PMN and fibroblasts that is optimal at approximately 10 nM. hFpB causes a rapid, dose-dependent increase in PMN cytoskeletal associated actin, but unlike fMLP, hFpB does not cause PMN aggregation, release of lysosomal enzymes (lysozyme and beta-glucuronidase), or the production of superoxide anion. These results suggest that hFpB may have a role in recruiting PMN and fibroblasts at sites of fibrin deposition and turnover. The capacity of hFpB to cause PMN chemotaxis without causing concurrent release of lysosomal enzymes or the production of superoxide anion is further evidence for the complexity of PMN responses to chemotactic agents.