The hydrolysis of 1-methyl-2-cyano, 4-cyano-, and 3-cyanopyridinium ions by aqueous base has been studied. The kinetics of the reaction of the 2- and 4-cyano derivatives were measured by polarographic analysis of cyanide ion formation, and the rate of reaction of the 3-cyano ion was followed spectroscopically at 3500 Å. The 2- and 4-cyano ions yielded the corresponding pyridones and carbamidopyridinium ions, while the 3-cyano ion formed 3-carbamidopyridinium ion and 4-cyano-5-methyl-amino-2, 4-pentadienal. The ratios of the products varied in each case with pH. The ratio of carbamidopyridinium ion formation rates for the three isomers was 50:5·7:1 (2-:4-:3-) with a second-order rate constant for the 3-isomer of 0·28 1 mol-1sec-1. The rate ratio for attack on the pyridinium ring was > 1100:43:1 (2-:4-:3-) with a rate constant for the 2-isomer of ∼76 1 mol-1 sec-1 at 25°.