Conjugated linoleic acid (CLA) is the fatty acid group of compounds with conjugated double bonds in the intermole-

compounds with conjugated double bonds in the intermolecule of linoleic acid. CLA was discovered by Kepler et al. in 1966. It has been described as an anticarcinogenic agent in grilled ground beef. Recently, CLA has gained explosive popularity with athletes and body builders in the U.S.A. based on reports of body fat reduction and lean body mass enhancement attributed to it. CLA exerts diverse physiological actions against carcinogenesis, arteriosclerosis, diabetes, and cardiovascular disease. The immune system is also affected by CLA. CLA modulates certain aspects of immune defense, including increased lymphocyte blastogenesis, macrophage phagocytes, and lymphocyte proliferation. On the other hand, in the superfluous immune response, CLA increases the production of IgA and IgG, promoting the allergic response through their reduction, while reducing IgE by promoting the allergic response through a superfluous increase in lymphocytes. CLA was also found to stimulate moderate production of arachidonic acid and arachidonate-derived eicosanoid, including COX-2 activity or expression. CLA inhibits the release of cytokines, histamine, and prostaglandin-E2 (PGE2) 16) from immune cells. These reports led us to expect that CLA would inhibit the anaphylaxis (type I hypersensitivity reaction) and allergic pruritus by affecting chemical mediators. This paper describes the inhibitory effects of CLA against anaphylaxis using a blood pressure (BP) or blood flow (BF) monitoring assay system and against allergic pruritus using a scratching (itch-associated response) measuring assay system.