A serially transplatable tumor model was established by inoculating subcutaneously the surgical specimen of a patient with mixed type small cell lung carcinoma into nude mice (BALB/C nu/nu). A human small cell lung carcinoma cell line cultured in vitro was established from that tumor in nude mice. The cultured cell line gave a typical growth pattern with small round feature, cell clusters in suspension and float growth. Pathological sections of both the patient's tumor and transplantable tumor in nude mice showed the same morphological features. The typical APUD granules were observed in electron transmission microscopy. The transplantable tumor has been transferred for 9 passages in 14 months and the cell line in vitro for 71 passages in nearly one year.