The electrochemical reduction of thioisonicotinamide NRCSNH2 has been examined in an aqueous medium between H-0 = - 1 and pH = 13.7. As shown by cyclic voltammetry and polarography, a global 2e(-) 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(-) reduction of NRCSNH2 to the formal diionized form NRC-(SH)(NH3+), the first chemical reaction, C-1, being a formal proton transfer which yields the 4-gemaminosulfanylmethylpyridine; the rate constant of this reaction is 2 x 10(4) s(-1) in acidic medium and diminishes in neutral medium. The second process, C-2 which is much slower, is actually made up of two reactions in parallel (with loss of NH3 or H2S), whose rate constants are in the ratio 4 to 1; the thioaldehyde and the imine which result from these reactions are easier to reduce than thioisonicotinamide. A comparison of the rates of deamination and dehydrosulfuration with those of dehydration and deamination previously obtained during the reduction of isonicotinic acid, isonicotinamide and their derivatives is made.