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 strongly absorbs light at .
3,5-Dinitrosalicylic acid can be prepared by the nitration of salicylic acid:
It was first introduced as a method to detect reducing substances in urine by James B. Sumner. It has since been widely used (for example) for quantifying carbohydrate levels in blood. It is mainly used in assay of alpha-amylase, however enzymatic methods are usually preferred due to DNS's lack of specificity.