Based on our new concept of ontogenic inflammation, we have sought a substance which can prime macrophage in terms of the endogenous production of tumor necrosis factor (TNF). A lipopolysaccharide (LPSw) was found in wheat flour, purified and characterized. The molecular size of LPSw was about 5 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it contained 3-deoxy-D-manno-octulosonic acid: 1, hexosamine: 4 and one phosphorus in a single molecule. LPSw can prime macrophage to release TNF when given intradermally, percutaneously or even orally in mice as well as in humans, in exactly the same way as intravenous administration of interferon gamma.