A human rectal poorly-differentiated adenocarcinoma cell line HR-8348 is established from the surgically removed tumor mass of a male adult patient. The cell doubling time is 36.05 h. The mitotic index is 44.5%. The cells are all of epithelial type and mostly of polygonal shape. Electron microscopic examination shows malignant nuclei with enlarged nucleoli; there are abundant microvilli and some secretory granules. The plating efficiency in soft agar is 12.9%. In PHA (1 microgram/ml), the cells show obvious agglutination. Chromosomal analysis reveals a mode of 70 chromosomes per cell, with a marker chromosome. CEA in cells is detected positively both qualitatively and quantitatively. Hetero-transplantation of the cells to nude mice shows that the tumor mass has the same morphology as the original mass from the patient, with Alcian blue positive material in the cytoplasm. Repeated detection for mycoplasma contamination shows negative.