The biologic effect of roentgen irradiation depends on absorption of the rays applied to the site of the pathologic process. In different cutaneous lesions this site is situated at different levels in the skin and subcutaneous tissues; hence it is necessary to determine the optimal quality and quantity of radiation to use in each specific case. It was therefore deemed advisable to determine the amount of radiation of the qualities used in dermatologic practice which is absorbed in successive millimeters of skin. MATERIAL AND METHOD Determinations of absorption were made with live and dead rabbit skin, ear and thigh, fresh human skin obtained from the operating room, water and aluminum. Our measurements were all made in air, to avoid the effect of scattering. The apparatus used was a mechanical rectifier with a universal type Coolidge tube. The peak kilovoltage was 100, the milliamperage was 3 and the skin focal distance