The steps in the evolution of sulfamoyl diuretics in current clinical use are outlined. The development was initiated by the chance observation of a clinical side effect of sulfanilamide, which became the first sulfamoyl group (-SO2NH2)-bearing compound used for diuretic treatment of patients. Ensuing chemical synthesis over the past three decades led to the development of three types of sulfamoyl diuretics:carbonic anhydrase inhibitors, thiazides, and the loop or high-ceiling saluretic agents represented by furosemide and bumetanide. The structural relationship of furosemide to sulfanilamide and the thiazide-type diuretics and, for bumetanide, the more specific structure for loop diuretic activity are discussed.