Tast polarography, differential pulse polarography and cyclic voltammetry were applied to the examination of 7 derivatives of 3-carboxy-4-hydroxy-6-acetylaminoazobenzene with H, CH3, OCH3, Cl, COCH3, NO2 and NHCOCH3 substituents in position 4'. A general reduction mechanism was suggested for the substances. The half-wave potentials obtained from tast polarographic measurements were correlated with the Hammett σ constants of the substituents in the para-position. The plot of this dependence is linear, which suggests that the reduction mechanism is identical within the entire series. The optimum conditions for quantitation of the substances were found within the concentration regions of 1 .10-4 to 1 .10-6 mol l-1 for tast polarography and 1 .10-4 to 1 .10-7 mol l-1 for differential pulse polarography.