The reaction of N-methyl-2-pyrrolidinone with CS2 has been found to take place at elevated temperatures (> 200 degrees C) in high yields, but the theoretical study for this reaction revealed the activation energy to be as high as 140 kcal mol(-1), which made this reaction an impermissible process. Conflicts between the theoretical study and experimental finding made us reinvestigate the mechanism of this reaction in detail, using density functional theory at the B3LY-P/6-31G(d) level. Our research suggested a simple addition-elimination mechanism, in which the activation energy was calculated to be only 36 kcal mol(-1); this result corresponds well with the experimental finding. (c) 2005 Elsevier B.V. All rights reserved.