Ventilation scintigraphy using Munsch's technique with Xenon 133 combined with perfusion scintigraphy using 99m Tc albumin particles in microspheres are of considerable interest in the preoperative evaluation of bronchogenic carcinoma. Basing themselves on 95 cases, the authors discuss the manner in which the tumor affects ventilation and perfusion. In the 70 cases of matching ventilatory and perfusion scans, scintigraphy alone is not sufficient to demonstrate the exact perfusion obstruction mechanism. On the other hand, if there is a V/Q mismatch (21 cases) and if the perfusion defect is more extensive than the ventilation defect or the radiological opaque area, this normally implies a mediastinal extension of the tumor, and tends to make any carcinologically valid ablation highly risky. Comparison of the perfusion and ventilation scans with the radiological data and spirometric values showed that 9 patients presented with abnormal pulmonary radiographs outside the tumor areas. Six of these cases involved tuberculous sequelae. Forty-four of the ninety five patients (46.3%) showed normal ventilation and perfusion scans outside the tumor areas. Of the 91 patients undergoing spirometry, 39 suffered from ventilatory obstruction and pathological ventilation and perfusion scans and 18 presented with scintigraphic anomalies outside the tumor are a but did not suffer from ventilatory obstruction.