[en] A study of the lungs of aged subjects have shown that the structural malformations of old age and the physiopathologic reflexes which follow, result in a reduction of elastic tension, an unhomogenous distribution of ventilation, hemodynamic alterations resulting from the reduction of the capillary network and cardiac flow and, finally, modifications of gas exchange. Among the various techniques and radioisotopic methods which could be used for the determination of these manifestations, the following are quite interesting: the use of ⁹⁹Tc for the measurement of circulation time; the use of macroaggregates labeled with various radioelements for the obtention of scintigraphic documents and to attempt to perform quantitative evaluations according to the criteria of various orientation; the adoption of regional perfusion techniques correlated, naturally, with clinical and functional tests. Intrathoracic circulation time was measured with gamma-camera images and direct magnetoscope recording after intravenous pertechnetate injection; it was found that in aged subjects, the circulation time was at the upper limit of normal values. When macroaggregates and radioactive microsphere are utilized it is essential to establish the influence of age on the perfusion scintigram. This is done by quantitative and qualitative processes of evaluation and by studying the correlation of these values with functional tests