The epidermal growth factor receptor (EGFr) is a transmembrane glycoprotein detected on many cells and tissues including neoplastic and normal kidney. EGFr binds the mitogenic polypeptide hormone epidermal growth factor (EGF) as well as EGF-related transforming growth factor-alpha (TGF-alpha). Increases in EGFr gene expression and protein production have been implicated in the development of the malignant phenotype for certain cancers. To determine if alterations in EGFr gene expression are present in human renal cell carcinoma, paired samples of normal and neoplastic renal tissue from ten patients with advanced renal cell carcinoma were analyzed for EGFr mRNA content by Northern blot hybridization. The EGFr gene was constitutively expressed in 90% of normal kidney samples. In seven out of nine evaluable patients, tumors expressed 1.7 to 8.4 times more EGFr mRNA than corresponding normal tissue. Two patients showed no elevation of tumor EGFr mRNA and one patient had no identifiable EGFr transcripts in either neoplastic or normal kidney. Expression of EGFr mRNA was also detected in three tumor-derived and two established renal cell carcinoma cell lines. EGFr transcripts were not found in tumor infiltrating lymphocytes (TIL). These findings suggest that overexpression of EGFr mRNA may be associated with malignant transformation in renal cell carcinomas.