We immunohistochemically examined the expression of transforming growth factor-beta (TGF-beta) on tissue specimens from primary 124 human lung adenocarcinoma, using a polyclonal antibody. The overall mean immunoreactivity of TGF-beta was 25.7 +/- 22.9, therefore we separated patients into two groups according to their mean immunoreactivity. There were 59 (48%) with a high TGF-beta and 65 (52%) with a low TGF-beta. No correlation was observed between the expression of TGF-beta and clinicopathological factors except for degree of differentiation. The 5-year survival rates of patients with high and low TGF-beta were 71% and 37%, respectively (P < 0.05). A multivariate analysis using the Cox life table regression model showed TGF-beta to be a significantly independent factor. We thus concluded, based on our findings, that the expression of TGF-beta was found to be related to a better prognosis. Therefore, estimating the negative cell proliferation activity induced by TGF-beta on immunohistochemical technique is considered to be useful for determining the patients' prognosis in cases of lung adenocarcinoma.