We have examined the c-myc gene expression and the gene organization in resected human esophageal squamous cell carcinomas, and in the adjacent normal esophageal mucosa from 20 patients undergoing radical surgery. Immunohistochemistry of p62c-myc was compared with that of proliferating cell nuclear antigen (PCNA) in order to examine the biologic significance of p62c-myc. Relative c-myc expression detected by Northern blot analysis ranged from 0.41 to 2.8, but the degree of c-myc expression did not correlate with other clinicopathological prognostic parameters. In sity hybridization localized the elevated c-myc mRNA expression to tumor cells and basal and parabasal cells of the adjacent normal mucosa. Immunohistochemistry showed altered localization of p62c-myc, i.e., both cytoplasmic and nuclear immunostaining in advanced carcinomas. c-myc immunoreactivity exhibited wider distribution compared with that of PCNA, a cell cycle related antigen, which may indicate induction of cell proliferation by p62c-myc. DNA hybridization showed mild amplification in one out of 17 tumors and no evidence of gene rearrangement. There was no distinct correlation between the results of Northern or Southern blot analysis and the results of in situ hybridization or immunohistochemistry. Gene alteration of the c-myc locus, as well as overexpression of the c-myc oncogene, appeared to be limited, and analysis of the c-myc gene yielded limited prognostic value in human esophageal carcinomas.