Abnormally high expression of epidermal growth factor receptors (EGF-receptors) may contribute to the unregulated growth of some tumors. We here report the EGF-receptor numbers and the effects of epidermal growth factor (EGF) on two human cell lines. The glioblastoma cell line T-MG1 had 135,000 EGF-receptors per cell, was slightly growth stimulated by EGF and showed no obvious change in morphology after exposure to EGF. The carcinoma cell line T-CAR1, derived from a brain metastasis of a carcinoma of the adrenal cortex, had approximately 7 million EGF-receptors per cell. EGF had a significant antiproliferative effect on these cells and caused rounding and detachment of cells in adherent cultures. The cell lines may become useful in future studies concerning the role of the EGF-receptors in malignant growth.