Abstract: Improved liquid, urea-sulfuric acid compositions noncorrosive to stainless steel contain about 5 to about 75 weight percent urea, about 5 to about 85 weight percent sulfuric acid, 0 to about 75 weight percent water and a corrosion inhibiting amount of a cupric ion-containing compound, in which the urea and sulfuric acid together comprise at least about 25 weight percent of the composition, and in which at least a portion of the urea and sulfuric acid are present as monourea sulfate, diurea sulfate or combinations thereof. The compositions may also contain amounts of selected dialkylthioureas sufficient to reduce their corrosivity to carbon steel.