Epidermal growth factor receptor (EGF-R) was estimated in Hypernephroma by saturation analysis using 125-I EGF as ligand. Tissue levels of this oncogene related protein were increased five-fold (24 to 99 fmol/mg protein) in comparison with the surrounding tumor free tissue (3 to 18 fmoles/mg protein). There was no apparent correlation to the stage of tumor growth or tumor differentiation and there was no correlation of EGF serum levels with tumor growth. EGF serum levels in the tumor patients did not exceed levels in control patients.