Although there are many studies analyzing cytogenetic or molecular alterations of human renal primary tumors, there have only been a few reports addressing both questions on renal cell carcinoma (RCC) cell lines. We have therefore investigated an RCC cell line, namely KTCTL-26A, by banding techniques and simultaneous growth factor gene expression analysis. KTCTL-26A represents a well-defined stemline and sidelines in the near-diploid range with clonal aberrations involving chromosomes 2, 3, 5, 7, 9, 13, 16, 21, 22, and Y in structure and/or number. The predominant karyotypic changes were a partial loss of chromosome 3p (ie, 3p14) and a gain of copies of chromosome 7 (trisomy or partial tetrasomy). By Northern analysis, in KTCTL-26A we found underexpression of the proEGF-gene (located on chromosome 4) and overexpression of the genes for proTGF-alpha and the EGF-receptor, which are located on chromosomes 2 and 7, respectively. By Southern blot analyses there was no evidence for an amplification in the case of the EGF-R and proTGF-alpha genes. Because these changes of gene expression were observed in both the cell line and in primary kidney tumor samples, they seem to be of constitutive (and not adaptive) nature. Hence, KTCTL-26A can serve as a model for the study of the origin of these molecular alterations and as a preclinical model for their genetic manipulation (e.g., by using antisense-oligonucleotides) for therapeutic purposes.