We have developed a technique for evaluating pulmonary blood perfusion which is essentially noninvasive. The technique is based on an electronic sampling circuit which measures video voltages so that during television monitored image intensified medical fluoroscopy of the lung the small incremental change in lung density which occurs with each cardiac systole can be very accurately measured. We have confirmed through our experimental work that the pulsation is definitely due to arterial pulsation with only a small component being related to the retrograde pulsation through pulmonary veins. There is a small body of literature accumulated over the last 20 years suggesting that this small pulmonary densitometric pulsation changes dramatically in the presence of primary and secondary malignancies in the lungs. Several authors have suggested that the pulsation changes long before a tumor is visible on a chest x-ray. For that reason we have set up an experimental protocol to determine if the pulsation does indeed change with the presence of lung malignancy and if so, how early the changes are present. Our initial result with the first 25 patients is encouraging.