The characteristics of three Bacteroides species, Bacteroides distasonis, Bacteroides goldsteinii and Bacteroides merdae, were examined. 16S rRNA gene sequence analysis showed that B. distasonis, B. goldsteinii and B. merdae should not be classified as species within the genus Bacteroides. Although B. distasonis, B. goldsteinii and B. merdae were phylogenetically related to Tannerella forsythensis, the ratios of anteiso-C15 : 0 to iso-C15 : 0 in whole-cell methanolysates of the three species were different from that of T. forsythensis. In addition, whereas the major menaquinones of T. forsythensis were MK-10 and MK-11, the major menaquinones of B. distasonis, B. goldsteinii and B. merdae were MK-9 and MK-10. The three species were phenotypically similar to Bacteroides sensu stricto, but phylogenetically distinct. Furthermore, B. distasonis, B. goldsteinii and B. merdae could be differentiated from Bacteroides sensu stricto (predominant menaquinones: MK-10 and MK-11) by the menaquinone composition. This is an important chemotaxonomic characteristic of the three species. On the basis of these data, a novel genus, Parabacteroides gen. nov., is proposed for B. distasonis, B. goldsteinii and B. merdae, with three species, Parabacteroides distasonis gen. nov., comb. nov. (the type species), Parabacteroides goldsteinii comb. nov. and Parabacteroides merdae comb. nov. The type strains of P. distasonis, P. goldsteinii and P. merdae are JCM 5825^T (=CCUG 4941^T=DSM 20701^T=ATCC 8503^T), JCM 13446^T (=CCUG 48944^T) and JCM 9497^T (=CCUG 38734^T=ATCC 43184^T), respectively.