The electron time decay in an afterglow following a short pulsed d.c. discharge in CO has been investigated using microwave diagnostic techniques. The gas was heated to an average temperature of 775 °K. Two-body electron-ion recombination and ambipolar diffusion were found to be the only important electron removal mechanisms present in the pressure interval [Formula: see text] Torr with the rate constants αr = 3.9 × 10−7 cm3 s−1 and Dap0 = 372 cm2 s−1 Torr respectively. If we postulate a T−γ dependence for αr, comparison with room temperature results yields γ = 0.57. The diffusion coefficient appears to increase strongly with temperature based upon an estimated zero field mobility for CO+in CO at 273 °K found in the literature.