2-Amino-6-nitro-1,3-benzo-thia-zol-3-ium 3-carb-oxy-4-hy-droxy-benzene-1-sulfonate.

In the title salt, C7H6N3O2S+·C7H5O6S-, the cation is protonated at the thia-zole N atom and the dihedral angle between the nitro group and its attached benzene ring is 3.6 (4)°. In the anion, the sulfonate group is deprotonated and the dihedral angle between the carb-oxy-lic acid grouping and its attached ring is 7.1 (4)° and an intra-molecular O-H⋯O hydrogen bond occurs. In the crystal, cation-to-anion N-H⋯O and anion-to-anion O-H⋯O hydrogen bonds link the component ions into (101) sheets. Aromatic π-π stacking and weak C-H⋯O and C-H⋯S inter-actions also occur.