Two human renal carcinoma cell lines have been established from the same patient. One cell line (CCF-RC1) was obtained from the primary tumor and the second (CCF-RC2) was established from cells of the renal vein effluent of the perfused tumorous kidney. Although they were established from the same patient, the cell lines differed in certain biological properties. They have been passaged up to 50 times in vitro for about two years. Each has an epithelial morphology and exhibits mutilayering. Cell cycle time of CCF-RC1 and CCF-RC2 was 34 and 36 h, respectively. They exhibited anchorage independent growth, and the plating efficiency of CCF-RC2 in soft agar was higher than that of CCF-RC1. Both lines induced tumors in nude mice at the site of s.c. injection closely resembling the original tumor in histological examination. Electron microscopic features of both tumors in nude mice were consistent with epithelial origin. Doubling time of CCF-RC1 and CCF-RC2 in nude mice was 11 and 12 days, respectively. CCF-RC1 and CCF-RC2 have hypotetraploid karyotype and modal numbers of 83 and 73, presenting two and three marker chromosomes, respectively. Immunocytology with commercial monoclonal antibodies against renal carcinoma (URO-3) and cytokeratin (Mac 6) showed positive reactions with both lines, suggesting that these cell lines derived from renal epithelium. A murine monoclonal antibody (2E11) was generated against CCF-RC2 by the hybridoma technique; 2E11 reacted with CCF-RC2, but not with CCF-RC1. These cell lines may provide a useful model for the study of tumor heterogeneity and its relationship to metastasis.