The initial step in renal secretion of organic anions (OA) is mediated by transporters in the basolateral membrane (BLM). Contributors to this process are the primary-active Na+/K+-ATPase (EC 3.6.3.9), the secondary-active sodium-dicarboxylate cotransporter 3 (NaDC3/SLC13A3), and the tertiary-active OA transporters OAT1/SLC22A6, OAT2/SLC22A7 and OAT3/SLC22A8. In human kidneys we analyzed the localization of these transporters by immunochemical methods in tissue cryosections and isolated membranes. The specificity of antibodies was validated with HEK293 cells stably transfected with functional OA transporters. The Na+/K+-ATPase was immunolocalized to the BLM along the entire human nephron. NaDC3-related immunostaining was detected in the BLM of proximal tubules and in the BLM and/or luminal membrane of principal cells in connecting segments and collecting ducts. The thin and thick ascending limbs, macula densa, and distal tubules exhibited no reactivity with the anti-NaDC3 antibody. In OAT1-3-related immunostaining in human kidneys was detected only in the BLM of cortical proximal tubules; all three OATs were stained more intensely in S1/S2 segments as compared to S3 segment in medullary rays, whereas the S3 segment in outer stripe remained unstained. The expression of NaDC3, OAT1, OAT2, and OAT3 proteins exhibited considerable interindividual variability in both male and female kidneys, and sex differences in their expression could not be detected. Our studies provide a side-by-side comparison of basolateral transporters co-operating in renal OA secretion in the human kidney.