This paper presents polarographic and voltammetric studies on the electroreduction of 2-chloro-4,6-diamino-1,3,5-triazine on mercury electrodes and in the acidity range 2.25 M H2SO4 to pH 10. Above pH 8 no signals were obtained. In dc polarography, a reduction wave was observed, being partially overlapped with the discharge of the supporting electrolyte. In differential pulse polarography, up to three waves were found, depending on the pH of the medium. The overall process corresponded to a four-electron irreversible reduction. The first small peak was attributed to the reduction of the depolarizer adsorbed on the electrode. In strongly acidic media the protonated depolarizer was reduced, the rate-determining step (rds) being the second one-electron transfer. In less acidic media, the protonation of the reactant at the heterocyclic N5 nitrogen precedes a two-electron reduction, the rds being a protonation placed between the reversible one-electron transfers to give a dechlorinated molecule (peak 2). The reduction of this product through a similar mechanism occurred at the potentials of peak 3. From the decrease of the limiting (and peak) current a value of ca. 10(11) s(-1) at pH 6.7 was found for the rate constant of the protonation reaction. (C) 2003 The Electrochemical Society.