In 34 patients with central bronchial carcinoma and in 28 patients with non-tumourous diseases of the bronchopulmonary system we investigated lung ventilation and perfusion with a self-made roentgen-functional method (x-ray cinepulmodensitometry) and an automated evaluation system. It appeared, that the automated evaluation of lung function with its high sensitivity facilitated the detection of small tumour-specific functional changes. Their early detection can improve the differentiation of lung carcinoma from non-tumourous lesions.