The electrochemical behaviour of several phenolic compounds of biological interest in vegetable materials was studied. Oxidation potentials of the examined compounds and voltammetric curves of some representative phenols are reported. As a practical application of electrochemical detection in HPLC, the analysis of monomeric units emanating from nitrobenzene oxidative hydrolysis of wheat straw lignin is described. Electrochemical detection simplifies the analysis, permitting the direct injection of the reaction mixture without interference from nitrobenzene. Aniline formed by the reduction of nitrobenzene is also detectable and may be used as an oxidisability index of the vegetable matter.