Twenty-eight odontogenic abscesses were examined for the presence of black-pigmented Bacteroides spp. Of the 28 samples, 26 were found to contain one or more species of black-pigmented Bacteroides. Abscesses were divided into three categories according to the tissue of origin: endodontal, periodontal, and pericoronal. Four abscesses which developed after extraction were also examined. It was found that Bacteroides endodontalis, a newly described species of asaccharolytic black-pigmented Bacteroides, was isolated almost exclusively from periapical abscesses of endodontal origin. B. intermedius proved to be the most frequently isolated species in all of the samples. B. gingivalis was present in all of the periodontal abscesses studied, as well as in two endodontal abscesses. B. melaninogenicus was recovered once from a pericoronal abscess. Precautions for the isolation of B. endodontalis are discussed. Abscesses in the maxillofacial region are the most frequently occurring pyogenic infections in oral surgery. These infections are almost always of odontogenic origin. They may be classified according to the primarily infected tissues: endodontal (periapical), periodontal, and pericoronal. Other infections may be postoperative or may be caused by needleborne infections, jaw fractures, skin lesions, or extractions. Early research on the bacteriology of these kinds of infections suggested a major role for the viridans streptococci (13, 14). However, since the improvement of anaerobic sampling and cultivation techniques it was found that the majority of the microbiota of these abscesses consisted of obligately anaerobic microorganisms (1, 3, 5, 11). Within this group of bacteria gram-negative rods often are encountered. In addition, many other types of bacteria can be isolated, e.g., facultative and obligately anaerobic cocci and rods. Until now, few attempts have been made to correlate the different forms of dental abscesses with certain bacterial floras or specific combinations of bacterial species. Researchers in bacteriology often did not differentiate among the various forms of odontogenic abscesses, making correlation with the microbial flora involved impossible. Oguntebi and co-workers (12) found Fusobacterium spp. and Strepto