4-Hydroxymandelic acid is a chemical compound used to synthesize atenolol.

[1] The compound typically occurs as a monohydrate.

It is produced from 4-hydroxypyruvic acid by the action of the enzyme (S)-p-hydroxymandelate synthase: 4-Hydroxymandelic acid can be synthesized by the condensation reaction of phenol and glyoxylic acid:[1]