The gene for resistance to erythromycin and clindamycin, which is carried on the conjugative Bacteroides plasmid, pBF4, has been shown previously to be part of an element (Tn4351) that transposes in Escherichia coli. We have now introduced Tn4351 into Bacteroides uniformis 0061 on the following two suicide vectors: (i) the broad-host-range IncP plasmid R751 (R751::Tn4351) and (ii) pSS-2, a chimeric plasmid which contains 33 kilobases of pBF4 (including Tn4351) cloned into the IncQ plasmid RSF1010 and which is mobilized by R751. When E. coli HB101, carrying either R751::Tn4351 or R751 and pSS-2, was mated with B. uniformis under aerobic conditions, Emr transconjugants were detected at a frequency of 10(-6) to 10(-5) (R751::Tn4351) or 10(-8) to 10(-6) (R751 and pSS-2). In matings involving pSS-2, all Emr transconjugants contained simple insertions of Tn4351 in the chromosome, whereas in matings involving R751::Tn4351, about half of the Emr transconjugants had R751 cointegrated with Tn4351 in the chromosome. Of the Emr transconjugants, 13% were auxotrophs. Bacteroides spp. which had R751 cointegrated with Tn4351 in the chromosome did not transfer R751 or Tn4351 to E. coli HB101 or to isogenic B. uniformis, nor did the intergrated R751 mobilize pE5-2, an E. coli-Bacteroides shuttle vector that contains a transfer origin that is recognized by R751.