Phenylhydrazine is the chemical compound with the formula C6H5NHNH2 or C6H8N2. Organic chemists abbreviate the compound as PhNHNH2. It exists as yellow to pale brown crystals or as a yellowish oily liquid and has an aromatic odour. It is the first hydrazine derivative characterized and reported by Emil Fischer in 1875. This compound is used worldwide mainly as a chemical intermediate in the pharmaceutical, agrochemical, and chemical industries. Its derivatives were used firstly as antipyretics but the toxic action on red blood cells made their use dangerous. However, this compound seems to be very useful in models studying mechanisms of haemolytic anemia.