The electrochemical behaviour of biphenyl, naphthalene and t-butylbenzene in saturated solution in 0.5 M H2SO4 was studied by means of differential electrochemical mass spectrometry (DEMS) in the region of negative potentials versus SHE. Desorption of molecular species was detected mass spectrometrically. In the case of naphthalene the hydrogenated species were also detected. The relative amount of species available fair oxidation before and after desorption was estimated.