The O serotypes of uropathogenic Escherichia coli isolated in Korea were studied using a complete set of rabbit O antisera raised with reference O antigen type strains of E. coli. The distribution of "O" serotypes found in this survey was grossly similar with the prevalence of "O" types observed in other parts of the world, and some differences were also noted. A total of 31 "O" serotypes were identified and the most frequent serotype associated with urinary tract infections was O75(11.5%), which was followed by O6(7.4%), O10 and O40(5.7%, respectively).0 and O40(5.7%, respectively).