Leukotriene B(4) (LTB(4)) is a lipid mediator associated with innate immune function. LTB(4) is produced mainly by polymorphonuclear leukocytes and macrophages and plays important roles in host defense. However, LTB(4) is also associated with inflammation, and excessive production of LTB(4) can result in inflammation, allergic reactions, and carcinogenesis. Regulation of excessive LTB(4) production may therefore assist in controlling these conditions. In this study, we investigated the capacity of 7 strains of lactic acid bacteria to inhibit LTB(4) production by the murine macrophage cell line J774.1. All strains tested inhibited calcium ionophore (A23187)-stimulated LTB(4) production in macrophages, but to varying extents. Lactobacillus helveticus Bc-10 exhibited the highest level of inhibitory activity. The inhibitory activity of strain Bc-10 was sustained after heat-killing and was observed in the intracellular cell-free extract prepared from this strain. This is the first report that intact lactic acid bacteria and their isolated cellular components can directly inhibit LTB(4) production by macrophages, and provides a useful method to screen the inhibitory activity of lactic acid bacteria. This study also highlights the potential of the strain Bc-10 as a treatment option for the regulation of LTB(4) production in vivo.