Primary human mammary carcinomas were found to contain an acid stable polypeptide which bound to the receptor for epidermal growth factor (EGF). This polypeptide which was antigenetically different from EGF and thus identified as Tumor Growth Factor (TGF) alpha, could be identified in 25% of the tumors. Among these tumors 40% contained measurable levels of the EGF receptor. Thus these tumors exhibit the molecular prerequisite for autocrine growth stimulation.