The renal kallikrein-kinin system seems to participate in the regulation of blood pressure, control of sodium and water excretion, renal vascular resistance and renin release. By using ultrastructural immunocytochemistry, in situ hybridization or polymerase chain reaction experiments with the appropriate cDNA probes, kallikrein and kininogen were observed to exist and be synthesized in different types of cells of the nephron. Recently, new finding of a kinin receptor has been reported, since specific kinin receptor antagonists have become available. The localization of components of kallikrein-kinin system in the kidneys and its relation to renal function is discussed.