PCR was used to identify antibiotic resistance determinants in 31 Canadian Salmonella serovar Typhimurium DT104 isolates. Genes encoding resistance to ampicillin (pse1 or blaP1), chloramphenicol (pasppflo-like), streptomycin-spectinomycin (aadA2), sulfonamide (sulI), and tetracycline [tet(G)] were mapped to a 13-kb region of DNA of one isolate. Two copies of sulI were identified and mapped to the 3' end of either pse1 or aadA2 integrons. The two integrons were separated by the pasppflo-like gene and the tet(G) gene. The kanamycin resistance determinant (aphA-1) was present on a 2.0-MDa plasmid (five isolates) or on the chromosome (three isolates).