Electron‐microscopic examination of normal bronchial epithelium and mucous glands has revealed the presence of cells similar in appearance to Kultschitzky (argentaffin) cells in the intestinal canal. The cells, which possess long cytoplasmic processes, are present in small numbers at all levels of the bronchial tree and are found adjacent to the basement membrane. They contain characteristic cytoplasmic granules referred to as neurosecretory‐type granules, which are similar to those present in intestinal argentaffin cells, adrenal medullary cells and sympathetic nerve endings. Eighteen bronchial carcinoid tumors and 22 oat‐cell pulmonary cancers have also been found to contain similar neurosecretory‐type granules in the tumor cell cytoplasm. On the basis of light‐microscopic similarities and the production of similar common patterns of hormonal disturbances and the possession of similar ultramicroscopic features, it is suggested that oat‐cell pulmonary cancer and bronchial carcinoid tumors are closely related. They may be, respectively, the malignant and locally malignant form of tumors derived from Kultschitzky‐type cells normally found throughout the bronchial tree.

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Nineteen papillary, non-invasive tumors arising from the bronchial epithelium but excluding carcinoid tumors are reviewed. Eight were solitary papillomas of which three were covered with a mixture of epithelial types. Seven were benign but one had a focus of carcinoma in situ. A similar change was seen in bronchial epithelium adjacent to a papilloma. Two cases of recurrent papillomas were seen and in one, carcinomatous changes eventually occurred. Two combined benign brochial cystadenomas with papillomas are described. One transitional celled papillary carcinoma in situ and five other papillary carcinomas in situ are described. One bronchial papilloma covered with dysplastic epithelium was considered an intermediate stage in the development of carcinoma in situ. Two papillary tumors may have arisen from peripheral bronchi or brochioles. Their lining cells resembled Clara cells, they grew by local expansion, and there was an absence of malignant features. The differential characteristics of two secondary carcinomatous polypoidal tumors are described.

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