Phenidone (1-phenyl-3-pyrazolidinone) is an organic compound that is primarily used as a photographic developer.

[1] It also has low toxicity and unlike some other developers, does not cause dermatitis upon skin contact.

[2] As a developer, Phenidone is typically used in conjunction with hydroquinone for black and white photography and performs better at lower pH levels.

It is oxidized in acidic conditions, contributing the electrons it loses to reduce silver halides such as those found in film:[6] Phenidone is also a dual cyclooxygenase/lipoxygenase inhibitor, capable of blocking the synthesis of arachidonic acid, which plays a role in causing inflammation in systemic inflammatory response syndrome[7] and neuronal damage in kainic acid-induced seizures.

[8] Phenidone can be prepared by heating phenyl hydrazine with 3-chloropropanoic acid.