Importance of project: In recent years many antibiotics have come to the foreground as a treatment for mastitis. Aureomycin is one of the more recent antibiotics that has been used for this purpose. Aureomycin has been reported to be successful in curing some types of mastitis, but milk produced by cows that have been treated with Aureomycin does not act normal in the cheese manufacturing process. The most noticeable effect in milk from cows treated with Aureomycin has been slow or complete cessation of acid production by bacteria in cultured dairy products; this has been especially true in the cheese manufacturing process. In the even of slow acid production, or complete cessation of acid production, the cheese produced is either of lower quality than would normally be exected, or the entire vat of cheese may be lost. In either case there is a definite advers effect on the dairy industry. Purpose of investigation: The purpose of this problem is to determine the percentage of Aureomycin necessary in milk to cause slow or complete cessation of acid production in the cheese manufacturing process, and to find a chemical or heat treatment that can be used to inactivate the aureomycin so that there will be no harmful effect in milk used to manufacture cheese.