The diagnosis of large cell carcinoma of the lung on the basis of hematoxylin and eosin (H & E) stains represents a heterogeneous group, both endodermally and non-endodermally derived, totalling about 16% of lung cancers. By the use of special stains, such as Kreyberg and Grimelius stains, this percentage can be sharply reduced, leaving a core group of about 10%, including giant cell and clear cell variants. This core group may show a variety of ultramicroscopic organelles that are insufficiently developed to alter the light microscopic characteristics on which the diagnosis depends. In a study of 1000 slides, large cell carcinoma constituted 6% of the squamous cell carcinoma slides and 21% of the adenocarcinoma slides, which was reduced to 3% by mucin stains. Giant cells predominated in 5% and clear cells in 10% of large cell carcinoma slides. Large cells also occurred in 12% of small cell carcinoma slides.