Perfusion of rat liver with vanillic acid yielded only one metabolite. In paper chromatography with three different solvent systems, the substance showed the same RF-values as vanillyolglycine (3-methoxy-4-hydroxyhippuric acid) and in mixed chromatograms there was only one single spot. After separation by column chromatography, the UV- and IRspectra of the reaction product were identical with those of 3-methoxy4-hydroxy-hippuric acid. During the perfusion experiment, the kinetics of the conjugation were investigated.