Granulocytes play a pivotal role in natural immunity. Under inflammatory conditions, granulocytes are universally primed by several agents, such as endotoxins and inflammatory cytokines. Primed granulocytes exert potent adhesiveness, chemotaxis, phagocytosis and reactive oxygen species (ROS) production, effectively eliminating invading agents. Reactivity against priming agents is known to vary with species; however, there have been few reports on the effects of priming agents on canine granulocytes. In the present study, we assayed the priming effects of lipopolysaccharide (LPS), recombinant canine tumor necrosis factor-alpha (rcTNF-alpha) and recombinant canine granulocyte macrophage colony-stimulating factor (rcGM-CSF) on canine granulocyte function in vitro. Isolated recombinant canine were primed with various concentrations of LPS, rcTNF-alpha and rcGM-CSF, and CD11b expression was assayed. Furthermore, actin polymerization, phagocytosis and ROS production were then assayed at primer concentrations where enhancement of CD11b expression was observed. LPS did not enhance canine granulocyte function. Phagocytosis and actin polymerization were not enhanced by priming agents; however, rcTNF-alpha and rcGM-CSF enhanced CD11b expression and ROS production in canine granulocytes. These results suggest that priming effects are mainly reflected in CD11b expression and ROS production, with rcGM-CSF and rcTNF-alpha having a priming effect similar to that observed in humans.