The results of antibiotic tests on bacterial pathogens freshly isolated from avian tissues and bovine milk are presented. Coliform isolates from the avian species showed an increased resistance to antibiotics while those which produced bovine mastitis had remained generally more sensitive. The staphyloccoci and streptococci isolated from bovine milk showed an increase in resistance to most of the antibiotics tested. The indiscriminate administration of antibiotics to livestock and poultry has no doubt encouraged the development of resistant forms of bacteria and has made treatment with such products less effective.