4-Acetyl-N,N-diisopropyl-1-benzylnicotinamidinium ion (ABNA(+)) and 1-benzyl-4-phenyinicotinamidinium ion (PhBNA(+)) were newly synthesized as NAD(+) analogues to examine the electron-transfer reactivity and the effects of metal ions on the reactivity in comparison with those of 1-benzylnicotinamidinium ion (BNA(+)) and 1-methyl-4-phenylpyridinium ion (MPP+) which has no amide or acetyl group. A remarkable positive shift in the one-electron reduction potential of ABNA(+) was observed in the presence Of Sc3+ which forms a 1:1 complex with ABNA(+) through both acetyl and amide groups, whereas no such shift in the presence of Sc3+ was observed for the one-electron reduction of MPP+ which has no acetyl or amide group. Similar but less positive shifts in the one-electron reduction potentials were observed in the presence Of Sc3+ for the one-electron reduction of BNA(+) and PhBNA(+) both of which have only one amide group. The rate of electron-transfer reduction of ABNA(+) is enhanced significantly by the complexation with Sc3+ to produce stable ABNA(.)-Sc3+ complex which has been successfully detected by ESR. The electron self-exchange rates of the MPP./MPP+ system have been determined from the ESR line width variation and are compared with those of the ABNA(.)/ABNA(+) system.