Abstract
The principles of renal excretion are descr. A filtration of the plasma takes place in the glomeruli of the kidneys although certain substances including the contrast media are also excreted by the tubular epithelium to the passing urine. The significance of this mechanism in urography as well as the effect of the amt. of contrast medium admn. is discussed. Expts. in animals and trials in healthy and diseased humans are descr. and discussed.