The electron mobilities, mu (e), and electron-ion recombination rate constants, k(r), in dense gaseous Ar and Kr with a small amount of N-2 or CH4 as a molecular impurity have been measured as a function of electric field strength using a pulse radiolysis dc-conductivity method combined with a new decay-curve analysis method in which a space-charge effect is taken into account to obtain more accurate values of k(r). The energy of electrons in recombination is controlled experimentally in two ways; one is heating-up by the electric field and the other is cooling-down by inelastic collisions with additive molecules. A large deviation of k(r) from the Debye theory obtained in the present experiment has been discussed in terms of the electron mean free paths and electron energies based on recent theories. (C) 2001 American Institute of Physics.