The electron-transfer kinetics of CpFeCp(CH2)(8)SH and of CpFeCpCO(2)(CH2)(8)SH monolayers cochemisorbed with n-octanethiol diluent on gold and silver electrodes have been measured in chlororethane/butyronitrile solvent over temperatures of 115-170 K by cyclic voltammetry and potential step experiments. Rate constants for CpFeCpCO(2)(CH2)(8)SH monolayers are smaller than those for CpFeCp(CH2)(8)SH monolayers by a factor approximately equivalent to insertion of two -CH2- groups. Activation plots of rate constants k(0) for CpFeCp(CH2)(8)SH and for CpFeCpCO(2)(CH2)(8)SH monolayers on gold give reorganization energies (lambda) of about 0.95 eV which is similar to 0.2 eV larger than predicted from dielectric continuum theory. Broadened voltammetric peaks and curved potential step ln(i) vs time plots indicate a kinetic inhomogeneity among the surface ferrocene population; the effects of this inhomogeneity appear to cause artificially small values of reorganization energies (0.02-0.34 eV) when cyclic voltammetric wave shapes and log(k(APP)) vs eta plots are analyzed for lambda. Preliminary results for rate constants k(0) for CpFeCp(CH2)(8)SH monolayers on Ag are similar to those on Au but with a smaller barrier energy.