86 patients suspected of primary lung cancer, referred to the National Tuberculosis Centre for fibreoptic bronchoscopy, were selected for this study to determine the relative value of the various types of respiratory cytology material in establishing a diagnosis and to identify the factors which influence the exfoliation of malignant cells. Prebronchoscopic sputa and bronchial bnishings were found to yield diagnostic cells most frequently. Hilar tumours arising from large bronchi, squamous and small cell anaplastic types were found to exfoliate cells most frequently. The study highlights the effectiveness of cytologic methods in the diagnosis of bronchogenic carcinoma. Cytologic evaluation may be the only method of confirming the diagnosis whcn biopsy is contraindicated. In the investigation of a patient thought to have lung carcinoma, good "deep cough-up" sputa shuld be first examined to prove a diagnosis before subjecting him or her to procedure like bronchoscopy.