3,5-Dinitrosalicylic acid (DNS or DNSA, IUPAC name 2-hydroxy-3,5-dinitrobenzoic acid) is an aromatic compound that reacts with reducing sugars and other reducing molecules to form 3-amino-5-nitrosalicylic acid, which absorbs light strongly at 540 nm. It was first introduced as a method to detect reducing substances in urine and has since been widely used, for example, for quantificating carbohydrates levels in blood. It is mainly used in assay of alpha-amylase. However, enzymatic methods are usually preferred to DNS due to their specificity.