Twenty-one esophageal cancer cell lines (KYSE series) have been established from the resected specimens of patients with esophageal cancer. Three lines, KYSE-30, KYSE-50, and KYSE-70, were derived from the implanted tumor of nude mice (initial passage); others were derived from resected specimens. Each cell line was morphologically distinct. Detailed cytogenetic analysis indicated that each cell line was karyotypically unique, and DNA fingerprint analysis showed no cross-contamination among cells. Doubling time ranged from 13.7 to 75.5 hours, and modal chromosome numbers ranged from 46 to 120. Most cell lines grew in monolayer, but two cell lines (KYSE-50 and KYSE-360) grew as floating cell aggregates. No correlation was demonstrated between the establishment of cell lines and cell differentiation. These cell lines are the first reported to be homogeneous and individually unique and may provide a useful model for the study of human esophageal cancer.