A 3.4kb cryptic plasmid, pRRI2, was isolated from Bacteroides ruminicola 223/M2/7 and used as the basis for a new Bacteriodes/Escherichia shuttle vector. Constructs were made incorporating pRRI2, a Bacteroides erythromycin/clindamycin resistance marker and the E. coli pUC8-derived vector pHG165. One of these, pRRI207 (11 kb), was capable of introduction into strains belonging to four different species of Bacteroides (B. uniformis, B. distasonis, B. thetaiotaomicron, or B. ruminicola) either by conjugal transfer from E. coli or by electrotransformation. pRRI207 carries several unique restriction sites derived from the pUC8 multiple cloning site. Only one of six B. ruminicola strains tested was used successfully as a recipient for pRRI207, indicating that further modifications to transfer procedures or marker genes may be needed for wider application in this species.