Phenylhydrazine is a widely used reagent in conjunction with sugars, aldehydes, and ketones. In addition, to its use in the synthesis of dyes; pharmaceuticals, such as antipyrin; cryogenin, and pyramidone; and other organic chemicals. The hydrochloride salt is used in the treatment of polycythemia vera.

 Phenyl-hydrazine is used to prepare indoles by the Fischer indole synthesis, which are intermediates in the synthesis of various dyes and pharmaceuticals. Phenylhydrazine is used to form phenylhydrazones of natural mixtures of simple sugars in order to render the differing sugars easily separable from each other.

Osazone test is a chemical test used to detect reducing sugars. This test even allows the differentiation of different reducing sugars on the basis of the time of appearance of the complex. This test is also termed Phenyl hydrazine test based on the reagent used for this test.

Phenylhydrazine is toxic by single exposure via the oral route  and is expected to be toxic by the inhalation and dermal routes (data from these routes of exposure are less clear).

PHENYL HYDRAZINE HYDROCHLORIDE AR