Dimercaptosuccinic acid (DMSA), also called succimer, is the organosulfur compound with the formula HO₂CCH(SH)CH(SH)CO₂H. This colorless solid contains two carboxylic acid and two thiol groups, the latter being responsible for its mildly unpleasant odour. It occurs in two diastereomers, meso and the chiral dl forms. The meso isomer is used as a chelating agent for treatment of heavy metal toxicity, and is a water-soluble and non-toxic substance. When radiolabeled with technetium-99m, it helps in diagnostic testing of renal function.