4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is an organic compound with the formula SC<sub>2</sub>N<sub>3</sub>H(NH<sub>2</sub>)(N<sub>2</sub>H<sub>3</sub>). The compound consists of a 1,2,4-triazole heterocycle with three functional groups: amine, thioamide and hydrazyl. X-ray crystallography shows that this molecule is polar but with a C=S double bond. It is prepared by the reaction of hydrazine with thiourea:
The compound has been used as a reagent for the colorimetric detection of aldehydes.