The 5S DNA of Xenopus laevis, coding for oocyte-type 5S RNA, consists of many copies of a tandemly repeated unit of about 700 base pairs. Each unit contains a "pseudogene" in addition to the gene. The pseudogene has been partly sequenced and appears to be an almost perfect repeat of 101 residues of the gene. The order of components in the repeat unit is (5') long spacer--gene--linker--pseudogene (3') in the "+" strand (or H strand) of the DNA. The possible function of the pseudogene is discussed.