A study has been made of the polarographic behaviour of genotoxic 1-[4'-(phenylazo)phenyl]-3,3-dimethyltriazene in mixed water-methanol medium. A mechanism has been proposed for its polarographic reduction and optimal conditions have been found for its determination by tast polarography in the concentration range 1 . 10 -4 - 2 . 10 -6 mol l -1 and using differential pulse polarography in the concentration range 1 . 10 -4 - 2 . 10 -7 mol l -1 .