Excretion rates in milk of sodium penicillin G, streptopenicillin, oxytetracycline, and chlortetracycline given to sheep by intramuscular injection or intramammary infusion were studied. When given by intramuscular injection, penicillin G and streptopenicillin were excreted in milk for 24h, oxytetracycline for 38h, and chlortetracycline for 72h. The corresponding times following intramammary infusion were 72 to 86h, 72 to 86h, 96 to 110h, and 110 to 120h. Concentrations in milk of penicillin, streptopenicillin, and oxytetracycline given by intramuscular injection made it unsuitable for yogurt production for 24h. Chlortetracycline, although excreted in milk longer, did not affect yogurt production. When antibiotics were given by intramammary infusion, they were excreted in milk in concentrations harmful for yogurt production for 72, 72, 96, and 116h.