Bacteriologic analysis of pathogens from pyogenic infections of the jaw in 71 patients revealed that bacteria normally found in the buccal cavity predominated in 86% of the specimens. Considering the fact that no pathogens could be identified in 7% of the specimens, this then means that pathogens were only found in 7% of the specimens. Six to 12 strains were usually isolated in the mixed bacteria population of the buccal cavity. A total of 430 strains of bacteria were cultured and tested for their response to 20 common antibiotic preparations. We were able to confirm the high effectiveness of penicillin and/or broad spectrum penicillin 92% of the cases (8600 determinations of resistance). Tetracycline was effective in 89% of the cases; trimethoprim sulfamethoxazole, in 83%. The effectiveness of newer, more expensive, antibiotic preparations was not significantly better than that of pencillin. Administration of such antibiotic preparations therefore should be limited to problematic pathogens.