According to a 1999 epidemiological survey by the Fatigue Study Group of the Ministry of Health, Labor and Welfare in Japan, 60% (47 million) of workers complained of fatigue. However, there have been no established recommendations for fatigue, and few anti-fatigue medicines or foods have been developed. Physical or mental load induces oxidative stress, resulting in fatigue. Accordingly, antioxidants are candidate anti-fatigue substances. Imidazole dipeptides (carnosine and anserine) have strong anti-oxidative effects, and chicken breast is rich in such dipeptides. The results of two human studies suggested imidazole dipeptides were effective and useful in attenuating fatigue induced by physical loads and daily activity. In short, imidazole dipeptides are novel anti-fatigue ingredients.