The filtered load of water, electrolytes and toxic substances of human kidney is huge. The largest part of this filtered load must be absorbed by renal tubules. Our understanding of the transport mechanisms, their regulations and mechanism of action of diuretics has been increasing during the last decade. Recently, the genes of Bartter syndrome and Gitelman Syndrome were identified and mutations have been found which lead to these syndromes. These important findings makes the diagnosis of the two recessive syndromes easy.