A tandem DNA duplication carried on a ColE1-derived plasmid segregates at high frequency upon generalized transduction by phage P22 HT. Transductional segregation of the plasmid-borne duplication can be promoted either by RecA or by the Erf function of P22, indicating that transductional segregation is a consequence of the recombination events that re-circularize the plasmid in the recipient cell. RecA-mediated and Erf-mediated transduction give similar frequencies of duplication segregation and yield the same types of segregation products, indicating that two distinct recombination machineries (RecA + RecBCD and Erf + RecBCD) perform similar or identical recombination reactions on plasmid DNA substrates transduced by bacteriophage P22 HT.