We investigated the phenotypic and genetic properties of metallo-␤-lactamase-producing Pseudomonas isolates collected at a tertiary-care hospital in Korea since 1995. The prevalence of imipenem resistance among Pseudomonas aeruginosa isolates reached 16% in 1997, when 9% of the resistant organisms were found to produce VIM-2 ␤-lactamase, a class B enzyme previously found only in P. aeruginosa isolates from Europe. VIM-2-producing isolates of Pseudomonas putida were also detected. Resistance was transferable from both these species to P. aeruginosa PAO4089Rp by filter mating, although the resistance determinant could not be found on any detectable plasmid. Serotyping showed that many of the VIM-2-producing P. aeruginosa isolates belonged to serotypes O:11 and O:12, and pulsed-field gel electrophoresis of XbaI-digested genomic DNA revealed that many had identical profiles, whereas the P. putida isolates were diverse. Sequencing showed that the bla VIM-2 genes resided as cassettes in class 1 integrons. In contrast to previous VIM-encoding integrons, the integron sequenced from a P. aeruginosa isolate had bla VIM located downstream of a variant of aacA4. bla VIM also lay in a class 1 integron in a representative P. putida strain, but the organization of this integron was different from that sequenced from the P. aeruginosa strain. In conclusion, the metallo-␤-lactamase produced by these imipenem-resistant Pseudomonas isolates was VIM-2, and the accumulation of producers reflected clonal dissemination as well as horizontal spread. Strict measures are required in order to control a further spread of resistance.Carbapenems such as imipenem are stable to most ␤-lactamases. Nevertheless, the first isolate of Pseudomonas aeruginosa with transferable imipenem resistance due to a metallo-␤-lactamase production was reported in Japan in 1991 (26). The enzyme produced by this isolate almost certainly was IMP-1, which subsequently has been repeatedly found in Japan, not only in P. aeruginosa and Acinetobacter baumannii (23), but also in Serratia marcescens (14) and other members of Enterobacteriaceae (5). Rasmussen and Bush (18) predicted that the increasing use of carbapenems would select for more carbapenem-hydrolyzing organism on a wider scale, and this prediction is now proving correct. Several close relatives of IMP-1 have been reported during the past 3 years: IMP-2 from an isolate of A. baumannii in Italy (19), IMP-3 (MET-1) from Shigella flexneri in Japan (6), and IMP-4 from Acinetobacter and Citrobacter spp. from Hong Kong, China (3).Descriptions of IMP-5 to IMP-8 enzymes are understood to be in press. IMP-1 to IMP-4 have at least 80% homology to each other, but in 1999, a new type of acquired metallo-␤-lactamase, VIM-1, was reported to have been found in an isolate of P. aeruginosa collected in Italy (8). Soon afterwards, isolates of P. aeruginosa with a related enzyme, VIM-2, were reported in France (16,17). Since then, outbreaks of VIM ␤-lactamaseproducing P. aeruginosa have been reported in Greece (25) and Italy (...