Barrett's Esophagus (BE) is a complication of gastroesophageal reflux in which the normal squamous epithelium of the lower esophagus is replaced by metaplastic tissue. The clinical significance of this condition is the associated predisposition to adenocarcinomas (ADCs). Three types of BE have been characterized: the gastric fundic (F) type, the gastric cardial (C) type, and the intestinal (I) type. The latter is the most closely associated with the development of ADCs; the causes of this bias remain unknown. To determine whether p53 and/or K-ras gene alterations (a) are present in preneoplastic lesions and (b) are associated with a specific histotype, we performed PCR-based denaturing gradient gel electrophoresis (DGGE) analysis of exon 1 (codons 12-13) of K-ras gene and of exons 5-8 of the p53 gene in biopsies obtained from 30 patients with BE of the I type (9 patients), combined I type (I + C +/- F; 10 patients) and non-I type (C, F, or C + F; 11 patients). None of the cases under study revealed K-ras mutations, whereas biopsies from 12 patients showed at least one p53 DGGE variant. Four patients showed the exact same variants in leukocytes also (polymorphisms), whereas eight cases revealed specific DGGE variants only in biopsies. The molecular characterization of these variants revealed that four of them showed a single base pair substitution, and four showed multiple mutations. Of 17 somatic mutations, all but 1 were base pair substitutions located mainly in exons 7 and 8. The majority of these mutations were GC targeted (13 of 16; 81%), 54% (7 of 13) of which were transitions occurring at CpG sites. All somatic mutations were found in BE with at least one I component. The association with the histotype was statistically significant (P < 0.03; pure I type versus non-I type; P < 0.04, combined I type versus non-I type; Fisher's exact test). Loss of heterozygosity in the vicinity of the p53 locus was evaluated by PCR using a highly polymorphic variable number of tandem repeats marker on 25 out of 30 cases. Ninety-two % of the cases analyzed were informative, and none of them showed LOH. In conclusion, we showed that p53 mutations are frequently observed in specimens from BE patients of the I-type, whereas no involvement of K-ras (exon 1) mutational activation was observed. In light of the key roles that the p53 protein plays in controlling cell cycle and cell diploidy, this result may suggest why this type of metaplasia is the most closely associated to the development of ADCs.