The primary purpose of sputum cytology is to detect preinvasive and invasive malignancy. Candidates for the screening procedure include long-time smokers with productive cough, patients chronically exposed to asbestos, patients with hemoptysis, persistent cough and/or weight loss, and asymptomatic patients with x-ray lesions or unexplained pleural effusions. The procedure is inexpensive and highly diagnostic. Five consecutive specimens produced by deep coughing are required for adequate evaluation.