After X-rays were detected and cystoscopes had become available, progress in nephrology depended on the development of contrast media which would permit imaging of the kidneys and the urinary system. We describe how A. Binz and C. Räth, two chemists at the Agricultural Academy in Berlin, synthesized iodinated derivatives which were potent chemotherapeutics. Moses Swick tested the substances in the clinics of L. Lichtwitz (Hamburg) and A. von Lichtenberg (Berlin) and discovered a rapid renal excretion. He also observed that an iodinated N-acetylated derivative, later named Uro-Selectan, amplified X-ray contrast after intravenous application. With this substance and other derivatives which were produced by Schering-Kahlbaum AG, the door was open for excretion urography.