Mycotoxins secondary metabolites of microscopic fungi- are classed with the most dangerous contaminants of food products and fodders which occur in natural conditions. Mycotoxins are distinguished by high toxicity and many of them possess mutagenic, teratogenic, and carcinogenic properties. At present we know more than 250 species of various microscopic (mould) fungi which produce approximately 100 metabolites of varying toxicity giving rise to alimentary toxicity of man and farm animals. The facts accumulated in recent decades land themselves to a conclusion about universal spread both of mycotoxin producers and of toxins proper. There are all grounds to believe that the number of isolated mycotoxins will continue to grow with further study of the role of toxin-forming microscopic fungi in alimentary toxicoses of man and animals of unestablished etiology.