Three tumor cell lines (COLO 201, COLO 205, and COLO 206) have been established from ascites fluid obtained from a male patient with adenocarcinoma of the colon. In addition to the tumor lines, two lymphoid lines (COLO 197 and COLO 200) have been established from the same patient, with one line from the original biopsy and one from peripheral blood. Characterization of the tumor cell lines revealed four cell types that differ from most colon cell lines reported by others. Chromosome markers were identical in COLO 201 and COLO 205. A long-arm isochromosome 5 observed in COLO 201 and COLO 205 was absent in COLO 206. Statistical analysis of autosomal polysomy revealed that these cell lines were stable and indicated that there may be a cytogenetic basis for the three predominant types of cell morphology. The lymphoid cell line derived from the peripheral blood had a normal male karyotype. The lymphoid cell line derived from a biopsy specimen had a mode of 46 and a deleted chromosome 7 marker. Both lymphoid cell lines had B-cell characteristics. These autochthonous cell lines have been used for immunological studies in cytotoxicity assays and immunoglobulin characterization.