Epidermal growth factor (EGF) stimulates apoptosis in tumor cells depending on the expression levels of EGF receptor and Her2. We examined the protein levels in 22 different cancer cell lines and assessed the responses to EGF. EGF-induced cytotoxicity was not correlated with the levels of either EGFR or Her2. Fourteen cell lines exhibited decreased cell proliferation, whereas 293T cells did not display any noticeable changes and degraded transiently expressed EGFR following EGF treatment. EGF treatment resulted in significant tumor growth inhibition in some xenografts. Our data indicate that exogenous EGF treatment leads to growth inhibition rather than inducing tumor cell proliferation.