SummaryChanges in the excretion of Periston N by the kidney were studied with the unpublished method of Fergus and Levy, as modified by Zipf.In normal individuals the total amount of the injected Periston N is excreted within 24 hours folowing a typical excretion curve.In various diseases (infections, cardiac diseases, drug intoxications, hepatitides, renal diseases) a retention or a slowing of the excretion of Periston N were observed.In some cases, Periston N seems to have influenced the course of the disease although renal failure was not influenced.The renal excretion of Periston N seems to rely on at least three factors : the state of the circulation, some changes in blood chemistry and the renal function. The interpretation of the results needs an accurate evaluation of these various functions.