18 patients with pulmonary tuberculosis and ventilatory insufficiency had a differential spirometry with determination of the following parameters in each lung: oxygen uptake, ventilation, vital capacity and diffusing capacity. Lung scintigraphy was also performed. The factors influencing the diffusing capacity of each lung were the ventilation and the pulmonary arterial blood flow because there was a high correlation between each of these parameters and diffusing capacity – 0.9702 and 0.9634, respectively.