In modern nuclear medicine, renal function scintigraphy has been improved and its range of applications extended by the development of new radiopharmaceuticals (iodine-123-hippuran, technetium-99m-MAG3) combining the properties of short half-life, favourable radiation energy and high renal clearance. Three significant advantages recommend the use of scintigraphic methods: 1. Being non-invasive and non-nephrotoxic, the examinations do not affect the patient. The radiation exposure the patient is subjected to is about the same as with a comparable X-ray investigation or, with respect to the reproductive glands, even lower. Allergic reactions do not occur. 2. In contrast to the situation with other imaging methods, the functional defect itself (and not only secondary changes in the morphology) can mostly be detected. Not only diffuse alterations, but also defined functional lesions of a small part of a kidney, can be diagnosed. 3. Various renal parameters can be calculated more accurately than with any other routine clinical method. The radioisotopic methods discussed yield reliable results with excellent reproducibility concerning glomerular filtration rate, effective renal plasma flow, side-to-side functional ratio, renal perfusion, and urine drainage. Most of these parameters can be obtained by means of a single investigation. These radioisotopic methods make it possible to detect or exclude a wide range of functional lesions of the kidneys and the urinary tract, which are often due to non-specific symptoms. In addition, they allow answers to highly specific clinical and scientific questions in nephrology and urology.