Abstract
Investigations in an experimental model system and in clinical material indicate that squamous bronchial carcinoma is regularly preceded by the occurrence of bronchial cells with DNA values exceeding significantly the normal 4c region. The studies also show that cytomorphological methods do not allow the discrimination between milder forms of atypia and nonspecific cellular alterations. We describe a combined cytomorphological and cytochemical diagnostic procedure which facilitates the distinction between atypical squamous cells and nonspecific cellular changes in the bronchial tree.