Aflatoxins (AFs) are very important mycotoxins due to their extremely high toxicity, carcinogenic activity for animals (including humans), and frequent occurrence in various foods and feedstuffs. AFB1, AFB2, AFG1, and AFG2 are especially important AFs. The AFB, is well known as one of the most carcinogenic compounds. AF-M group are metabolites of AF-B group in feeds for cattle. Ingested AFB1 is converted to AFM1 in the cow's liver.The regulations on AFs have been established in many countries, with the maximum levels ranging from 1 to 20μg kg⁻¹ for AFB1 and from 0 to 15μg kg⁻¹ for AFM1. Because AFM1 is a metabolite of AFB1, regulation on AFB1 in feed for cattle is most effective for controlling AFM1 in milk.AFs are found in nuts, cereals, spices, dairy products, and the like. The contamination levels in commercial foods vary with natural and artificial causes.Because detoxification or elimination of AFs in foods is hardly possible, efforts to avert the occurrence of AFs in foods are important.Sterigmatocystin, a precursor of AFs, is also toxic and carcinogenic, but much less toxic than AFB1.