Three cases of alpha-fetoprotein (AFP)-producing lung carcinoma were studied histologically and immunohistochemically. Samples were obtained from two men and one woman who ranged in age from 64 to 71 years. Serum AFP levels for the three samples were 9826, 74.4 and 24.3 ng/mL. One case was classified as stage IIIA and two as stage IIIB. Two cases were diagnosed as large cell neuroendocrine carcinoma, and AFP expression was detected immunohistochemically. One of these samples showed differentiation to a hepatoid carcinoma, while the other was combined with a squamous cell carcinoma. The remaining case was a squamous cell carcinoma, and AFP was detected in only some of the tumor cells. All patients died within 2 years. The Ki-67 labeling indices of the AFP-producing pulmonary carcinomas (30.2 +/- 4.6%) were significantly higher than those of AFP-negative pulmonary carcinomas (P < 0.05). The high proliferative activity, advanced stage at presentation, vascular endothelial growth factor expression and vascular invasion observed in these tumors may explain the poor prognosis of AFP-producing lung carcinomas.