To decrease the energetic cast of reduction process in electro-organic synthesis, a hydrogen gas-diffusion electrode (HDE) can be used as anode. Thus, the results of an investigation of the electrochemical synthesis of L-cysteine from L-cystine using a HDE are reported. The influence of both amine acids on the behavior of H-2 oxidation reaction was studied by voltammetry and by using a rotating disk electrode. Also a comparative study between the use of a HDE anode or a dimensionally stable anode in the synthesis of (L)-cysteine in a filter press cell was made. (C) 2001 The Electrochemical Society.