The electrochemical reduction of methyl isonicotinate NRCO(OMe) and its protonated form H+NRCO(OMe) has been examined in an aqueous medium between H-0 = 0 and pH 6.7. As shown by cyclic voltammetry and polarography, a global 2e-, 2H+ reversible transfer is followed by two successive first-order chemical reactions and a 2e-, 2H+ reduction (EC1C2E process). A mechanism is proposed, beginning with the 2e-, 2H+ reduction of YRCO(OMe) (where Y is N or H+N) to the formal diionized forms YRC(THETA)(OH2)+(OMe) or YRC(THETA)(OH)(OHMe)+, where the first chemical reaction C1 is an internal proton transfer which yields the hemiacetal YRCH(OH)(OMe); this is analogous to the internal proton transfer occurring in the case of nitronic acids in acidic media. The variations of the rate constant of this process with pH (5.2 x 10(2) s-1 < k < 8.7 x 10(3) s-1) are analyzed. The second chemical reaction C2, which is much slower (rate constant k(d) < 1.6 x 10(-3) s-1), involves the loss of a MeOH molecule (analogous to a dehydration) to give 4-pyridine aldehyde, which is itself easier to reduce than 4-methyl isonicotinate.