In cells derived from two human renal carcinomas only the precursor form of epidermal growth factor (EGF) was found. The binding assay revealed a high level of EGF receptor expression in both cell types tested. However, these receptors are not involved in the growth activity of the cells under in vitro conditions used. The source of DNA synthesis-stimulating activity found in conditioned media of the cells tested is discussed with respect to possible participation of TGF beta.