The efficacy of currently performed surveillance in patients with Barrett's esophagus (BE) is substantially compromised by shortcomings of dysplastic lesions as diagnostic markers. The aim of this study was to evaluate the possible role of p53 protein expression as complementary method in the diagnosis of neoplastic transformation in BE. A longitudinal study was performed. 41 patients were enrolled. The median time of surveillance was 46 months. 234 archival paraffin blocks containing a total of 627 biopsies were retrieved. p53 protein immunostaining by application of the monoclonal antibody DO-1 was performed. The results of immunohistochemistry were compared with the exact histopathological diagnosis and grading of dysplasia (no dysplasia, indefinite for dysplasia, low-grade dysplasia, high-grade dysplasia, carcinoma). In merely four of 206 nondysplastic mucosal sites p53 expression was found. However, p53 expression was detected with increasing frequency in sites indefinite for dysplasia (2/9), specimens with low-grade dysplasia (9/15), high-grade dysplasia (3/3) and the one with a carcinoma. This study shows a close association of nuclear p53 protein expression to the process of neoplastic transformation in Barrett's epithelium. However, it apparently does not precede the appearance of dysplasia significantly. Thus, nuclear p53 expression as detected by immunohistochemistry may serve to confirm a suspected diagnosis of dysplasia in BE.