One hundred and fourteen patients with asbestosis, 59% of whom were chronic cigarette smokers, were subjected to a cytological sputum examination which showed: 36 workers (31.6%) with squamous metaplasia, 20 (17.5%) with benigh columnar cell atypia, 5 (4.4%) with benign dysplasia, 2 with suspicious cells for carcinoma, and 1 with anaplastic (microcellular) carcinoma. Clinically and histologically five lung cancers were verified, two of which were cytologically false negatives. All asbestosis patients with lung cancer were chronic smokers. Of the 114 asbestosis patients, 49 (43.0%) had ferruginous bodies in their sputum. The workers from an asbestos quarry more frequently had ferruginous bodies in their specimens than the other patients. Radiographically moderate and severe asbestosis cases showed squamous metaplasia more frequently than those with radiographically slight asbestosis. Most of the detected cellular atypias represented reversible alterations of the respiratory epithelium. It is, however, important to screen the sputum of older (greater than 40 years of age) smoking asbestos workers with benign and suspicious cellular atypias regularly because these alterations may represent the first step int he pathway to bronchogenic cancer. The results of this study did not answer the question of whether bronchial cancer of patients with asbestosis is curable if detected early with cytological methods.