The x-ray output of a 5.6 MeV linear accelerator was collimated to a 3 mm beam and passed through a patient. X-rays scattered from a small volume of tissue were accepted by a large focusing collimator behind the patient and reached a liquid scintillator, while the direct beam was absorbed. The x-ray beam and collimator were arranged to scan the patient. Light from the scintillator modulated the brightness of a cathode-ray tube spot, whose movements corresponded with that of the beam, building up a picture of the density variations in the focal plane. The tissue thickness observed was effectively 2.5 cm at a focal distance of 15 cm from the collimator face. The lateral resolution was 3 mm and density resolution 4%. A number of live scans were made over areas 15 X 18 cm2, in times of 50 seconds. In a comparison with tomography using inanimate objects, a superior resolution was obtained with the present technique. The method can be developed far beyond its present level to provide clinical information as yet unattainable and with the possibility of national screening.