PURPOSE: The DPC4/Smad4 gene is known to perform a key role in the TGF-beta group protein signaling pathway, which regulates cell proliferation, differentiation and death. DPC4/ Smad4 gene mutation has been studied in cancers of the breast, ovary, esophagus, colo-rectum, bile duct, as well as the pancreas. The mutation rates depend on the kind of carcinoma sites, and range from 10% to around 50%, but no study has been performed on gallbladder carcinomas. This study was performed to search for mutation of the DPC4/Smad4 gene in the gallbladder carcinomas. METHODS: Eighteen surgically resected gallbladder cancers were screened for mutation of the exons; 8, 9, 10 and 11 of the DPC4/Smad4 gene using dideoxyfingerprinting (ddF), and single strand conformational polymorphism (SSCP). The results were confirmed using automatic DNA sequencing, and the expressions examined by immunohistochemical staining with the monoclonal anti-DPC4/Smad4 protein antibody, B8. RESULTS: DdF revealed 3 mutations in two of the exons, which were confirmed by direct sequencing. In one case, a single-base substitution mutation existed in exon 11 with codon change (missense mutation), whereas in two cases such mutations were detected in exon 9 without codon change (silent mutation). Immunohistochemical staining showed negative to weakly positive expression for all three mutated cases, but had high false-positive rates (7/11). CONCLUSION: DPC4/Smad4 gene mutation exists in a certain proportion of gallbladder carcinomas, but the mutation rate seems to be low compared to organogenetically related pancreas or bile duct carcinomas. This suggests somewhat different mechanisms may operate on the carcinogenesis of these organs.