Out of 440 dentogenic pyogenic infections, 171 exclusively caused by anaerobes were investigated to understand the importance of anaerobic bacteria in dental pyogenic processes better. Grampositive anaerobic bacteria dominated. The predominant grampositive isolates in monoinfections were Peptostreptococci and in the case of mixed infections, strains of the genus Eubacterium. Strains of Prevotella and Porphyromonas dominated the gramnegative anaerobic spectra. The resistance to penicillin was very low. Altogether, only one strain of Prevotella oris and one strain of Prevotella oralis showed resistance to penicillin.