We have analysed the expression of p53 at the mRNA level, and extensively at the protein level by immunostaining, Western blotting, and ELISA measurements revealing a p53 increase in 8 out of 14 cell lines established from human pancreatic carcinomas. The mRNA levels closely paralleled the protein levels in most of the cell lines. Overexpression of p53 in tumor cells correlated with mutations in the p53 gene. Immunocytochemistry was also performed with tissue cryosections showing a nuclear p53 staining in 8 out of 12 exocrine, and 2 out of 2 endocrine tumors. In addition, nonmalignant peri-tumoral tissue specimens and cells derived from pancreatic juice of acute pancreatic patients were also positively stained. These findings may suggest functions of p53 in stress situations induced by acute inflammation or tissue regeneration. Genomic mutations in the tumor suppressor gene were associated with point mutations in either codon 12, 13 or 61 in the c-K-RAS oncogene in about two-thirds of cell lines. The frequent activations of a RAS oncogene in combination with mutations of a tumor suppressor gene are likely to contribute to the malignant phenotype of pancreatic adenocarcinomas.