The electrochemical behaviour of 5-(nitrophenyl)-1,2-dithiole-3-thiones and 5-(nitrophenyl)-1,2-dithiole-3-ones was studied by cyclic voltammetry in DMF The standard reduction potentials of 5-(p-nitrophenyl)-dithiolethione and 5-(p-nitrophenyl)-dithiolone entered into a linear correlation involving standard reduction potentials of substituted nitrobenzenes and known electronic constants of several substituents. This correlation allowed the determination of the electronic effects of [3-thioxo-1,2-dithiole]-5-yl and [3-oxo-1,2-diothiole]-5-yl groups which were, respectively, sigma(p)(-) = 1.14 and sigma(p)(-) = 0.86, comparable with those of nitro or cyano substituents.