This report revises the interpretations of the reaction mechanism in the polymerization of N-cyclohexylmaleimide (CHMI) in the presence of alpha, alpha'-azobis(isobutyronitrile) (AIBN) and (R, R)-N, N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminatocobalt(II) (1) [Macromolecules 2000,33, 1489]. Although we proposed that the reaction was mediated by a radical species and that the interaction between growing polymer radical with 1 induced chirality in the main chain in the earlier report, the results in the present article indicate that the systems reported in the earlier report were most probably contaminated by a small amount of air and that the polymerization proceeds via an anionic species that was produced by the interaction of the monomer, 1, and O-2. The effect of the contamination was overlooked due to the lack of a control experiment using O-2 in the absence of AIBN in our earlier study. In this work, the polymerization of CHMI was performed in the presence and absence of 1, O-2, alpha, alpha'-azobis-(isobutyronitrile) (AIBN), and protonic additives (methanol and acetic acid). The results indicated the following: (1) the polymerization in a tetrahydrofuran-pyridine mixture occurs in the presence of 1 and a small amount of oxygen even without using AIBN; (2) the reaction does not take place in the presence of 1 alone or in the presence of 1 and AIBN under a strictly controlled N-2 atmosphere; (3) a small amount of AcOH completely inhibits the polymerization with 1 and O-2 while 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) does not kill the reaction; and (4) the polymer was likely to possess -OH or -OOH groups at the chain terminals (a telechelic structure). On the basis of these observations, we withdraw our earlier, wrong interpretation that the polymerization is mediated by a radical species and conclude that the polymerization and the observed stereochemistry are effected by an anionic mechanism.