Dimetridazole is a nitroimidazole-based compound with antibacterial and anticoccidial activity. It was once widely used in the treatment of parasitic infections in poultry, cattle, swine and farmed fish until suspected to be carcinogenic and mutagenic to humans. Hydroxy dimetridazole is a metabolite of dimetridazole that may be useful for identifying this nitroimidazole in various agricultural samples through liquid chromatography-tandem mass spectrometry and other methods.