We immunohistochemically examined 131 primary human lung adenocarcinomas for the possible presence of autocrine factors. Transforming growth factor α (TGFα) 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 TGFα, 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 TGFα and low TGFα were 36% and 85%, respectively (P < 0.05). The 5-year survival rates of patients with high EGF and low EGF were 25% and 77%, respectively (P < 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 TGFα or EGF and low TGFα 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.