We had developed a method for the selective cultivation of cancer cells in short-term which was simple and required minimal technical skills. There have been so far 23 cases of pulmonary small cell carcinoma in which long-term passage of more than one year and establishment of a cell line were successful by the culture method. In particular, from November 1982 to March 1987, there were 29 patients who were diagnosed as having pulmonary small cell carcinoma on preoperative cytodiagnosis and whose cells were primary cultured. In 24 (83%) of these, isolation could be carried out in a short period and stable passage was possible. Long-term passage of more than one year and establishment of a cell line were successful in 21 (72%) of the 29 patients. As a result of primary culture of small cell carcinoma cells, a pattern of a suspended colony was observed in 22 (88%) of 25 cases. As passage advanced, the tendency toward attachment to the basal surface increased. The changes in dynamics of proliferation after long-term passage of more than one year were divided into three types: epithelial like cell type was observed in 8 (32%), the neurite like cell type was observed in 4 (16%) and the suspended colony type was observed in 13 (52%) of the 25 cases. Variant clones composed of relatively large cells appeared as a result of long-term passage or the use of carcinostatics in some pulmonary small cell carcinoma cells.