Fluoretec-M is a polyvalent conjugate used in direct fluorescent-antibody staining for identification of the Bacteroides asaccharolyticus-Bacteroides melaninogenicus group. The Fluoretec-M reagent detected all oral and nonoral test strains of B. melaninogaenicus subsp. intermedius, all test strains of B. melaninogenicus subsp. melaninogenicus, and the nonoral strains of B. asaccharolyticus. However, the Fluoretec-M polyvalent reagent and the monovalent conjugates which constitute Fluoretec-M did not detect the oral strains B. asaccharolyticus. The use of Fluoretec-M can therefore generate false-negative results in studies of specimens from oral cavity and from nonoral sites in which an infection with B. asacacharolyticus of oral origin may have taken place. It is suggested that antibodies reactive with the oral antigenic type of B. asaccharolyticus be included in the preparative procedure of the Fluoretec-M reagent.