The electrochemical behavior of both herbicides is qualitatively similar. The two-electron reduction of atrazine (2-chloro-4-ethylamino 6-isopropylamino-1,3,5-triazine) proceeds only in acidic media where the preceding protonation takes place (pK = 1.44). In solutions of higher pH (2-4) the observed reduction current is kinetically controlled by protonation and the estimated value of the protonation rate constant is k(r) = 2400 +/- 400 mol(-1) 1 s(-1). The products of reduction were identified by large-scale electrolysis followed by GC-MS analysis. The electron transfer reaction causes cleavage of the Cl atom and loss of the ethyl group yielding the respective products in the ratio approximately 4:1. The electrochemical properties of terbutylazine are characterized by the protonation constant pK = 2.37 and rate constant k(r) = 1900 +/- 200 mol(-1) 1 s(-1).