The rate constants for proton transfer from the radical cation CpRu(PPh(3))(2)H-.+ to pyrrolidine and piperidine have been determined by derivative cyclic voltammetry in CH3CN. The kinetic isotope effects k(H)/k(D) at 20 degrees C are 2.7 for pyrrolidine and 2.3 for piperidine-surprisingly small for transfers that are almost thermoneutral. The rate constant for proton transfer from CpW(CO)(3)H to aniline in CH3CN has been determined from the effect of the aniline concentration on the rate of W --> W self-exchange; the kinetic isotope effect k(H)/k(D) at 25 degrees C is 4.2-surprisingly large for a transfer that is uphill by 5.5 pk(a) units.