Cefoxitin resistance, but not resistance to clindamycin, erythromycin, lincomycin, or tetracycline, was transferred by a conjugation-like process from Bacteroides thetaiotaomicron UN101, a clinical isolate haboring four kinds of plasmids, to other Bacteroides species. Of a sample of 20 cefoxitin-resistant transconjugants, 8 contained all 4 plasmids, 10 contained 1 to 3 plasmids, and 2 contained no plasmids.