It is shown that, over a narrow range of amplitudes, applied voltage pulses can deposit wall charges inside a discharge tube without causing breakdown of the interelectrode gas: these charges enhance the breakdown voltage of the interelectrode gas for subsequent pulses, and the enhancement decays exponentially with the pulse interval. The enhancement decays more rapidly when the temperature of the discharge tube is increased so as to reduce its surface resistance, which furnishes the main leakage path of the wall charges. It is suggested that breakdown voltages of closely packed, repetitively pulsed discharge tubes are frequently enhanced by wall charges.