Abstract: A process is described comprising neutralization with ammonium hydroxide of the reaction mixture generated by the hydrolysis of 2-hydroxy-4-methylthio-butyronitrile by sulphuric acid, so as to obtain an aqueous phase and an organic phase which, once separated, are subjected to evaporation to remove the ammonium sulphate formed. For the aqueous phase, this sulphate is removed as a byproduct; and for the organic phase, it is recirculated to the neutralization vessel. The 2-hydroxy-4-methylthio-butyric acid obtained from the organic phase is subsequently diluted with water and possibly stabilized with sulphuric acid. The product obtained is useful as a food supplement in animal diets.