In this study we investigated immunohistochemically the expression of p53 and c-erbB-2 proteins in 30 gall bladder adenocarcinomas, one carcinoma in situ, eight gall bladder epithelial dysplasias, and four cases of chronic cholecystitis. p53 expression could be found in 14 (47 per cent) adenocarcinomas and in two out of eight epithelial dysplasias. There were significantly more p53-positive grade II-III tumours than grade I tumours (P = 0.032 according to Fisher's exact probability test). c-erbB-2 expression was found in three (10 per cent) adenocarcinomas, but all dysplasias were c-erbB-2-negative. All three c-erbB-2-positive cases were also p53-positive. The results indicate that p53 mutations and c-erbB-2 gene alterations play a role in the neoplastic transformation of gall bladder epithelial cells. Co-expression of p53 and c-erbB-2 suggests that alterations of these genes might act in concert in the neoplastic transformation. The occurrence of p53 expression in gall bladder dysplasias suggests that p53 mutations could be an early event in the evolution of some gall bladder carcinomas, as has been suggested for some other types of tumours, such as lung squamous cell carcinomas.