Kininogen is the precursor of the kinin peptide, which binds to kinin receptors and mediates a broad spectrum of physiological effects. To understand the function of kinin in the kidney, we have identified the cellular localization of the human low-molecular-weight (LMW) kininogen and bradykinin B2 receptor mRNAs in the human kidney by in situ hybridization histochemistry. Kininogen mRNA was found in the juxtaglomerular cells, mesangial areas, epithelium of parietal and visceral (podocytes) layers of Bowman's capsule, proximal and distal tubules, thin and thick segments of Henle's loop, collecting ducts, and the endothelial cells of the blood vessels. B2 receptor mRNA was colocalized with kininogen mRNA in the kidney except the podocytes. The most intense signals were observed in the distal tubules and collecting ducts for both kininogen and B2 receptor mRNAs. No signals were observed in the interstitial cells and macula densa. Control sections did not stain with either the kininogen or B2 receptor sense riboprobe. A Northern blot showed that the expression of LMW kininogen is in the liver and the kidney. Reverse transcription-polymerase chain reaction Southern blot showed expression of B2 receptor mRNA in the endothelial cells, renal proximal tubular cells, and kidney. Our results show the sites of action of kinin in the human kidney and provide further insight into the physiological role of the kallikrein-kinin system on renal function.