Inflammation is localized response to foreign substance such as bacteria or in some instance to internally produced substances and has relation with immunity system. The macrophages plays a role in the development of the Iymphohaemopoietic system before and after birth, as well as in the natural and acquired immune responses of adult to immunogens, including infectious agents. NO have been suggested to play an important role in endotoxin-mediated shock and imflammation. In this study, we investigated the effect of Omisodok-eum on the production of NO. The Omisodok-eum inhibited the secretion of NO in LPS-stimulated mouse peritoneal macrophages, without affecting cell viability. The protein level of inducible nitric oxide synlhase(iNOS) in peritoneal macrophages was also decreased by Omisodok-eum. These results suggest that Omisodok-eum suppresses the endotoxin-induced inflammatory responses through inhibiting the production of NO