Reduction mechanisms of a series of alpha-dicarbonyl compounds that can be described as CEC are considered in this paper. The electroreductions of 3,4-hexanedione and methylglyoxal are investigated. Polarographic (dc and differential pulse), voltammetric and kinetic studies have been carried out. The effects of pH, reactant concentration, proton donors and, in voltammetry, scan rate on the electrochemical parameters were studied. The results indicate that both compounds are reduced through CEC mechanisms where the rate-determining step is a protonation reaction by any proton donor present in the medium. In the case of methylglyoxal the slowness of the dehydration preceding the reduction causes the process to appear as "pure kinetic" in linear sweep voltammetry. The results obtained here, together with those reported in the literature for other alpha-dicarbonyl compounds, are discussed. A parallelism in the electrochemical behaviour of these compounds is evident.