Seven cases of alpha-fetoprotein (AFP)-producing lung carcinoma were studied histologically to determine whether they fell into any previously described category. The patients were all males from 40 to 73 years of age and their serum AFP levels ranged from 1039 to 320,000 ng/ml. Five cases of hepatoid adenocarcinoma, one case of endodermal sinus tumour, and one case of papillary adenocarcinoma were found. The possible origins of the tumours and their differential diagnosis are discussed. Hepatoid adenocarcinoma is a major histological category among AFP-producing lung carcinoma; other types are less frequent. The occurrence of hepatoid adenocarcinoma in both the stomach and the lung suggests that this neoplasm may also be seen in other organs of endodermal origin. It may be a major histological subtype of AFP-producing endodermal neoplasms of non-germ cell origin.