G-banded chromosomes of primary cultures taken from mucosal epithelium adjacent to esophageal cancer (EC) were first analyzed. Consistent chromosomal changes, i.e. marker chromosomes, appeared in 2 of seven specimens of esophageal epithelium. Some of the marker chromosomes are very similar to those found in EC8501 cell line. These results imply that the cytogenetic analyses of the mucosal epithelium adjacent to EC may detect the numerical and structural chromosome aberrations occurring at the very beginning of carcinogenesis of esophageal epithelium.