The plasmid profiles of 97 Bacteroides isolates collected during screening for different pathogenic markers of this genus were investigated. In all, 48% of 69 isolates from infections that belonged to six species harboured low mol.wt plasmids (2.8-11.0 kb). Similar plasmids were also found in 39% of 28 isolates, belonging to eight species, from faeces of healthy persons. The two most frequently obtained types were the 5.5- and the 4.2-kb plasmids, which were present in 70% and 52% of all plasmid-bearing isolates, respectively. Restriction endonuclease analysis revealed that the 5.5-kb plasmids found in the different Bacteroides spp. exhibited the same restriction map, with the exception that pBVP61 lacked the PstI recognition site. The two plasmid types (4.2 and 5.5 kb) seem to be most widely distributed among Bacteroides isolates independent of the site of isolation and with some differences depending on geographic regions.