Even before the turn of the century, the dermatologist Leopold Freund tried to treat a hairy naevus on the back of a child with the rays Roentgen had discovered in 1895 when all known forms of therapy had failed. Loss of hair, as desired, resulted therein. In order to prove that electric currents were not the effective agent, Freund abducted them and treated another part of the naevus pigmentosus piliferus, however, for a longer period in order to compensate for the supposed loss of energy. An ulcer resulted. A number of renowned researchers doubted the biological effect of the X-rays. Freund also began to doubt his original opinion and later even attacked his very own discovery. Only the findings of Robert Kienböck, after having carefully examined them, let Freund accept his former opinion again. Guido Holzknecht, recognized as a pioneer of X-ray diagnosis even before the First World War, occupied himself successfully with X-ray therapy under the influence of Kienböck. He may be regarded as one of the world's first radiobiologists. Vincenz Czerny, of Austrian origin, and a pupil of Theodor Billroth, became a promotor of the X-ray therapy of malignant blastomas in Heidelberg. K. H. Kärcher, who has been head of the Department of Radiotherapy, Vienna University, for the past ten years is a graduate of this famous school.