WHEN supervoltage radiation became available for treatments one of the advantages claimed for it was that much heavier doses could be administered through the skin without damage. Lauritsen (1) made some calculations of the energy absorbed in the surface when one roentgen was measured in beams of various qualities. These calculations suggested but did not state that more than double the number of roentgens, as measured in air, could be given with 1,000 kv. than with 200 kv. radiations. In our experience this is not true in the practice of roentgen therapy. In the following discussion the term “high voltage” refers to the radiations from a 200 kv. General Electric X-P tube activated by a constant potential apparatus at 200 kv. and 15 ma., and filtered through the wall of the tube (0.2 mm. Cu equivalent) and 0.2 mm. Sn, 0.25 mm. Cu and 2 mm. A1, or 0.5 mm. Cu plus 1 mm. A1, as stated. “Supervoltage” refers to the radiations from the Sloan high frequency generator, operated at from 600 to 1,200 kv. and filte...