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These results point to some fundamen-tal difference or differences in the mode of action of antibiotics in the metabolism of chickens, turkeys, ducks and geese. A number of theories, with considerable evi-dence for each have been proposed to account for the action of dietary anti-biotics. These results lend some support to the suggestion that antibiotics may exert their effect by any one, or all, of several means. SUMMARY Aureomycin, diamine penicillin, pro-caine penicillin, streptomycin and terra-mycin increased the growth and feed efficiency of goslings to four weeks of age. With one exception the antibiotics also increased growth and feed efficiency from 4 to 8 weeks when the goslings were on grass range. All antibiotics improved feed efficiency to 8 weeks