Migration of bovine neutrophils towards endotoxin, recombinant bovine interleukin-1 beta (rBoIL-1 beta), recombinant human tumor necrosis factor-alpha (rhTNF-alpha), platelet-activating factor (PAF), complement factor C5a, leukotriene B4 (LTB4), and recombinant human interleukin-8 (rhIL-8) was studied in vivo, using the teat cistern model, and in vitro using the modified Boyden chamber method. Infusion of endotoxin, rBoIL-1 beta, rhTNF-alpha, PAF, or C5a into the teat cistern induced significant accumulation of leukocytes, mainly neutrophils, during the sampling period. Endotoxin was, on a molar basis, the most potent inducer of cell accumulation in vivo, followed by rBoIL-1 beta, while C5a, PAF and rhTNF-alpha were less potent. No significant cell accumulation was observed after infusion of LTB4 or rhIL-8. A significant migration of cells into the teat cistern was first observed 2 h after the infusion of endotoxin or rBoIL-1 beta, the rBoIL-1 beta-induced response started somewhat earlier. The first significant cell accumulation after infusion of PAF or C5a was observed already 1.5 h post infusion. The largest numbers of cells were reached 2.5-4.5 h after the infusion of endotoxin, rBoIL-1 beta, rhTNF-alpha, PAF or C5a. In vitro, significant migration of bovine blood neutrophils was observed towards C5a or rhIL-8, and to a lower extent towards LTB4, while no chemotactic response to endotoxin, rBoIL-1 beta, rhTNF-alpha, and PAF was observed. Possible roles of the different substances as inducers of neutrophil migration into the bovine teat are discussed.