A continuous cell line, U-1752, was established from a lung tumor originally diagnosed as a small cell carcinoma. The cell line has been in continuous in vitro passage for 29 months. The epithelial, rather than small cell nature of the U-1752 cells was demonstrated by the presence of desmosomes, prominent tonofilament bundles, by the reactivity with an anti-keratin antiserum and by the expression of cell surface receptors for epidermal growth factor (EGF). The U-1752 cells grow as monolayer cultures and have a population doubling time of around 36 hours at optimal growth in 20% calf serum. The most important neoplastic features of U-1752 were its aneuploidy, its capacity for colony formation in agarose and its tumorigenic potential subcutaneously in nude mice.