We investigated aspirates of pus from dentoalveolar abscesses in 13 patients who had received empirical antibiotic therapy within 1 month before presentation at our facility. The antibiotics administered were lincomycin, amoxicillin, ampicillin, or a cephalosporin. Information on antibiotic therapy was obtained from the patients' medical histories. Cultures of all dentoalveolar abscesses yielded organisms. A total of 70 isolates (42 anaerobes and 28 facultative organisms) were recovered, representing 5.3 isolates (3.2 anaerobes and 2.1 facultative organisms) per specimen. The counts of bacteria ranged from 5x10(7) cfu/ml to 8x10(11) cfu/mL (mean count, 1.4x10(11) cfu/mL; median count, 2.3x10(10) cfu/mL). The predominant isolates were Prevotella species (25.7% of isolates), Peptostreptococcus species (17.1%), and Streptococcus species (14.2%). This study illustrates the polymicrobial nature of dentoalveolar abscesses as well as the predominant role played by anaerobic bacteria.