The variants in enterotoxigenic Escherichia coli (ETEC) heat-labile toxin (LT) gene were detected by temperature gradient gel electrophoresis (TGGE). 15 clinical strains isolated from patients and a wild type strain (B2C) were analyzed after the conventional PCR. Although all PCR products (707bp) corresponded to A-subunit of LT, three strains were the different electrophoretic patterns after silver staining as compared to the wild type. For further electrophoretic analyses, the 707bp region was divided into 4 parts. The different ones were localized in the downstream part (183bp), but each those DNA bands was not so clear than DNA bands in 707bp. The clearer patterns were obtained by using a primer attached GC-clamp. The hetero-duplex assays in TGGE were proceeded by a series of procedures in mixing with the equal quantity of PCR products derived from a variant and a wild type, heat-denaturation and then annealing. TGGE of those mixed samples had 4 bands that were 2 front bands as homo-duplex and 2 slower migration bands as hetero-duplex. To Confirm the site of the mutations, the nucleotide sequences in each 183bp PCR products were decided by dideoxynucleotide-fluorescent dye method. Indeed, two variants were recognized four one-base substitutions without deletions and the one was five. Thus, the difference of migration in TGGE depended on the number and the localization in mutation sites.