The kidney is a key organ in the homeostasis of inorganic phosphate (Pi) and sulfate (Si). These anions are freely filtered at the glomerular capillaries and are then reabsorbed in the proximal tubule. Studies on isolated membrane vesicles allowed the identification of Na/phosphate and Na/sulfate-cotransporters. Subsequently these transporters have been cloned. Vesicle studies documented that physiological (and pathophysiological) alterations involve regulated transport rates of these cotransporters. Molecular studies using cDNA-probes and specific antibodies indicated that physiological regulation occurs at multiple cellular levels (e.g. transcription/translation and membrane traffic).