2-Hydroxy-4-(methylthio)butyric acid is an organic compound with the structural formula CH<sub>3</sub>SCH<sub>2</sub>CH<sub>2</sub>CH(OH)CO<sub>2</sub>H. It is a white solid. In terms of functional groups, the molecule is a ñ-hydroxy carboxylic acid and a thioether. The compound is structurally related to the amino acid methionine by replacement of the amine with a hydroxy group.
The compound is produced commercially in racemic form from acrolein by conjugate addition of methanethiol followed by formation and hydrolysis of a cyanohydrin. it is used as a substitute for methionine in animal feed.
In nature, the compound is also an intermediate in the biosynthesis of 3-dimethylsulfoniopropionate, precursor to natural dimethyl sulfide.