[The history of medical physics and biophysics at the Humboldt University in Berlin].
The present Institute of Medical Physics and Biophysics (former Institute of Radiation Research) was established on September 1st in 1923 by Walter Friedrich (1883-1968). It was after the Institute in Frankfurt A.M. (founded by Friedrich Dessauer in 1921) - the second Institute of its kind in Germany. As a physicist who wrote his dissertation under Wilhelm Conrad Röntgen, he did research together with a Gynecologist in Friedburg on problems of radiation therapy and the prevention of radiation injuries. Thus Friedrich became one of the first German Biomedical Physicists and was appointed to a professorship at the university of Berlin and its faculty of medicine. The paper gives a survey of the history of the Institute of Radiation Research in the twenties, in the time of Nazi-rule, the period after the World War II and in the era of GDR until 1990 and up to the present time. The succession of directorship of the Institute and the main research subjects in medical physics and biophysics have been sketched.