The milk samples of 39 cows that were at the end of the lactation period were collected aseptically. They were examined bact;riologically whether they were infected or not. Pathogenic bacteriae were isolated from 46 milk samples. Then, 46 infected quarters were treated by penicillin- streptomycin combatination. To determine the effectiveness of the treatment, milk samples were collected from the mammary quarters after calving and were examined bacteriologically. After calving 84.78% of these infected quarters were found to be free from infection. Streptococci and E. Coli were eliminated by 100% and staphylococci and C. bovis infections were eliminated 85% during the same period.