Four cases of generalized exanthemata were observed during X-ray treatment. The cause of this ailment is not thoroughly classified yet. Studying these cases, it will be said that the disease would develop on the ground of individual idiosyncrasy toward drugs and of decreased body resistance, because of observing most of the patients to who the same dose or more of Roentgentherapy was given as those four cases showed no system reactions. It is of importance that the use of drug having various reactions should be avoided with cares to improve patient's general condition, and diuresis especially to prevent pyelonephritis, during X-ray treatment.