We immunohistochemically examined 131 primary human lung adenocarcinomas for the possible presence of autocrine factors. Transforming growth factor alpha (TGF alpha) and epidermal growth factor (EGF) were considered growth factors with epidermal growth factor receptor (EGFR) as the receptor. Of these tumors, 87 (66%) showed a high expression of TGF alpha, 66 (50%) showed a high expression of EGF, and 55 (42%) were positive for EGFR reactivity. In the EGFR-positive cases, the 5-year survival rates of patients with high TGF alpha and low TGF alpha were 36% and 85%, respectively (P less than 0.05). The 5-year survival rates of patients with high EGF and low EGF were 25% and 77%, respectively (P less than 0.05). In contrast, in the EGFR-negative cases, there was no statistical difference between the 5-year survival rates of patients with either high TGF alpha or EGF and low TGF alpha or EGF. Because autocrine growth mechanisms are present in adenocarcinoma of the human lung, these events may contribute to clarification of tumor development, and perhaps even to a better prognosis.