The bacterial behaviour against antibiotics and pattern were examined with 88 strains of 10 species, isolated from pus collected in the infirmary of college of dentistry, and Seoul national university hospital during recent 7 years. 1. Isolated bacterial species and their relative incidences were, as follows, coagulase positive staphylococcus 50%, alpha hemolytic streptococcus 17%, Pseudomonas aeruginosa 10% and coagulase negative staphylococcus 8%. 2. Gentamycin reveals the highest sensitibity and cephalosporine follows it.