The goal of this investigation was to determine the practical role of cytopathology in the clinical and laboratory diagnosis of asbestos-related pulmonary diseases. For this purpose, sputum, bronchial washings, lung tissues, and pleural fluids were obtained from asbestos workers and controls. The asbestos-associated pulmonary diseases studied were: (1) asbestosis, (2) carcinoma, and (3) mesothelioma. The cytology smears were prepared with both Papanicolaou and iron stains. Lung tissues were digested by the Chlorox (5.25% sodium hypochlorite solution) technique for quantitation of asbestos bodies. Asbestos bodies within the sputum were found to be highly specific markers for past asbestos exposure, indicating a heavy residual pulmonary asbestos load (greater than 900 asbestos bodies/g wet lung weight). Asbestos bodies in sputum were also found to have a highly significant relationship (P less than 0.001) with the degree of accompanying atypia of bronchial epithelial cells. Bronchial washings appeared to be more sensitive than sputum for the detection of asbestos bodies. Asbestos bodies were not found within the pleural fluids of malignant mesotheliomas. It is concluded that sputum cytology screening represents a practical, noninvasive, and inexpensive approach to the diagnosis and study of asbestos exposure.