Trans-fatty acids are a type of unsaturated fatty acid in which the double bonds have a trans structure, as opposed to the cis structure often found in nature. Natural types of trans-fatty acids are produced in the first stomach (rumen) of ruminant animals and are known to accumulate in the milk and meat of these animals. A large-scale epidemiological survey in Europe and the U.S.A. has suggested that excessive intake of trans-fatty acids increases the risk of coronary heart disease. We have performed a comprehensive study of the amount of trans-fatty acids present in meat circulating throughout Japan to assess the current amounts of trans -fatty acids. The results reveal that the amount of trans-fatty acids in the type of beef (lean and fat) regularly consumed in Japan ranges from 0.33 to 1.87 g per 100 g. In addition, in beef fat, the amount of trans-fatty acids ranges from 1.43 to 9.83 g per 100 g. Among offal, rumen showed 1.70 g/100 g, the highest level. The results of this study indicate that, even between the same cuts, trans-fatty acid levels vary depending on the type of feed and duration of the grain-feeding period. In addition, in a study of pork and chicken, the amount of trans-fatty acids did not exceed 0.3 g/100 g in any part of the animal.