Urea transporter (UT) proteins, including isoforms of UT-A in kidney tubule epithelia and UT-B in vasa recta endothelia and erythrocytes, play an important role in the urine concentration mechanism by mediated an intra renal urea recycling, suggesting that functional inhibition of these proteins could have therapeutic use as a novel class of diuretic. Recently several classes of UT inhibitors have been identified and found to functionally inhibit UTs. A class of thienoquinolins, which specifically inhibit both UT-A and UT-B, exhibit diuretic activity. It is predicated that UT inhibitors have potential clinical applications as sodium-sparing diuretics in edema from different etiologies, such as congestive heart failure and cirrhosis.