The development of esophageal adenocarcinoma is frequently associated with intestinal-type Barrett's metaplasia. Barrett's metaplasia and esophageal adenocarcinomas were examined for expression of the intestinal brush-border-associated hydrolase aminopeptidase N (APN). APN mRNA was detected by utilizing the reverse transcription polymerase chain reaction (RT-PCR) in 50% of Barrett's metaplasia specimens and in 26% of esophageal adenocarcinomas. APN protein was detected by utilizing immunohistochemistry in 84% of Barrett's metaplasia specimens and in 71% of adenocarcinomas, although a decrease or loss of APN protein was sometimes observed in dysplastic Barrett's metaplasia and adenocarcinomas. Alterations in the p53 tumor-suppressor gene have previously been found in both dysplastic Barrett's mucosa and esophageal adenocarcinomas. The same specimens analyzed for APN were examined for the nuclear accumulation of the p53 protein. Utilizing immunohistochemistry, p53 staining was detected in 42% of Barrett's metaplasia specimens, most of which were dysplastic, and in 58% of adenocarcinomas. In the samples positive for p53 protein, gene mutations in exons 5, 7 and 8 were detected by utilizing single-strand conformation polymorphism analysis (SSCP) in 1 Barrett's metaplasia specimen and 6 adenocarcinomas. In Barrett's metaplasia, there was an inverse correlation between APN protein expression and p53 protein accumulation (p < 0.05) suggesting a link between genetic alterations and loss of this marker. The analysis of markers of intestinal differentiation with markers of disease progression may prove to be a useful approach for studying carcinogenesis in Barrett's metaplasia.