The growth-stimulatory effect of certain antibiotics on poultry and swine has been widely demonstrated during the past few years. The data relative to the effects of these substances on ruminants, however, are not so complete. Early work at the Oklahoma Agricultural Experiment Station with steers and at the Texas Agricultural Station with lambs indicated that aureomycin feeding resulted in anorexia and poor growth. In contrast, more recent studies at various agricultural experiment stations (Arkansas, Iowa, Kansas, Louisiana, New York-Cornell and Pennsylvania) have shown that aureomycin ingestion produces a growth stimulation and a reduction in incidence of scouring in young dairy calves. The levels at which aureomycin has been fed has varied over quite a wide range, but in most instances the amounts were far below those employed therapeutically.