A method of stabilizing low-pressure, high-power (100 kW) glow discharges against glow-arc transitions is described. An external circuit consisting of an inductor, a series resistor and a shunt capacitor is used to cause rapid arc extinction and avoid arc reignition. Mean power levels of 100 kW and peak powers of 160 kW have been sustained throughout many successive glow-arc transitions, and powers of 10 kW have been sustained for several seconds using a suitable d.c. power supply. The method may be suitable for applications such as electron beam glow discharge welding, neutron tubes, gas lasers, X-ray tubes, high-power transmitter valves, and microwave klystrons.