Regional lung function studies were obtained with a gamma camera. The ventilation was studied with 133Xe and radioactive particles and the pulmonary circulation with radioactive particles and the pulmonary circulation with radioactive particles. Some pathophysiologic patterns could be defined with this methodology, i.e. in chronic uncomplicated pulmonary embolism the pathophysologic pattern was normal ventilation with decreased or absent perfusion in the affected areas, when C.O.L.D. was associated with pulmonary embolism the ventilation with 133Xenon could be normal if the C.O.L.D. was mild but the inhaled particles deposited in foci. In bullous disease the inhaled 133Xenon reached the blebs with delay and that wash-out was prolonged, the particles did not reach the blebs, the perfusion was absent in the areas with blebs. Similar pattern was present in bronchial obstruction. In hilar masses the defect in perfusion and ventilation was usually larger than the one expected from the lesion.