Oligonucleotide probes which match consensus sequences of the repetitive extragenic palindromic (REP) element hybridize to genomic DNA of diverse bacterial species. Primers based on the REP sequence generate complex band patterns with genomic DNA in the polymerase chain reaction (PCR), a technique named REP-PCR. We used REP-PCR with genomic DNA to fingerprint 47 isolates of Citrobacter diversus. Previously, 37 were assigned electrophoretic types (ETs) by multilocus enzyme electrophoresis and 35 were evaluated by using outer membrane protein profiles. Fingerprints were compared by visual inspection and by similarity coefficients (SimCs) based on the number of common bands versus total bands between two given isolates. DNA fingerprints were highly similar visually for patient pairs and outbreak-related sets. SimCs for these were > or = 0.952. Fingerprints of isolates with different ETs generally were distinctive. Among 21 unrelated isolates representing 15 ETs, only 6 of 210 comparisons had SimCs of > or = 0.952. REP-PCR rapidly generated DNA fingerprints which were highly similar for epidemiologically linked isolates of C. diversus and distinct for previously characterized strains within this species. The ability of this method to discriminate between C. diversus isolates with the same biotype was similar to that of multilocus enzyme electrophoresis and outer membrane protein profiles. REP-PCR may be useful in evaluation of apparent outbreaks of this or other bacterial species which possess these extragenic, repetitive elements.