The electrochemical hydrogenation of anthracene and naphthalene is investigated with the aim of determining if the second electron transfer following the protonation of the anion radical occurs predominantly at the electrode (ECE) or in the solution (DISP). It is shown that double potential step chronoamperometry is a particularly sensitive method for discriminating between the two mechanisms. Indeed, a characteristic hump appears on the anodic trace in the case of ECE and not of DISP. Application of the method to the reduction of the two hydrocarbons in DMF in the presence of phenol confirms that anthracene hydrogenation follows a DISP mechanism. This is also the case for naphthalene which was previously thought to undergo an ECE-type reduction. The rates of protonation of the anion radical are derived from the ratio of the anodic to cathodic current intensities. Thus is confirmed by the statement that, in organic reactions, ECE mechanisms do not occur under conditions where they could be directly characterized by electrochemical kinetic techniques, i.e. when the system can be made at least partially reversible. The grounds and conditions of validity of this rule are discussed. For very irreversible systems, irreversibility arising from the rapidity of the chemical step and/or slowness of mass transfer, ECE reaction pathways may be followed. Indirect approaches for their characterization in such conditions are discussed.