The segregation of a bacterial plasmid, the sex factor F', has been investigated in a cell-division mutant of Escherichia coli which produces small anucleate cells (minicells). Significant amounts of isotopically labeled DNA segregate into minicells dependent upon the presence of F'. Minicells containing F'Gal or F'(lambda) are shown to donate the plasmid in conjugation. These results demonstrate that the sex factor may be dissociated from the bacterial chromosome and that this separation does not prevent its subsequent transfer.