4-cyano-l-methyl-pyridinium Perchlorate in acetonitrile has been investigated using d-c, normal pulse, and, in particu lar, reverse pulse polarography to elucidate the reduction mechanism at both the first and second waves. Reversible reduc tion to the pyridinyl radical occurs at the first wave. Reduction at the second wave leads to formation of an anion that can react with the parent pyridinium ion to form a dimer. The presence of small “hard” cations (such as protons or lithium ions) blocks this dimerization route on the Polarographie time-scale. The anion is more reactive to cations than the corresponding methoxycarbonyl substituted anion.