A skin unit was proposed in electrical terms by MacKee as that dose which produced a definite erythema on human skin of average radiosensitiveness and a temporary epilation of the hair of the scalp. For many years this skin unit has been used almost universally as the unit dose in treatment with nonfiltered roentgen rays of the various superficial lesions of the skin and scalp. These electrical terms were proposed for one particular type of equipment; therefore it seemed advisable to translate these terms into such units of radiation as could be produced accurately and safely with the newer equipment and roentgen tubes. The standard unit of roentgen dosage, called one roentgen is that dose which under normal conditions (0 C. and 760 mm. of mercury pressure) produces at saturation an ionization current of one electrostatic unit in a volume of 1 cc. of atmospheric air. It appears advantageous