Fibrinopeptide B, human is released from the amino-terminus of the B 3-chains of fibrinogen by thrombin. Fibrinopeptide B, human (hFpB, 10 nM) causes directed cell migration of neutrophils (PMN), and fibroblasts. Fibrinopeptide B, human also possesses potent chemotactic activity relative to human complement (C5a), leukotriene B4 (LTB4), and formyl-methionylleucyl-phenylalanine (fMLP), and for fibroblasts its chemotactic activity is comparable to that of platelet-derived growth factor. However, Fibrinopeptide B, human is not chemotactic for monocytes, and shows no interaction with PMN receptor for C5a, LTB4, or fMLP.