Abstract A measurement technique is described for use in corona-discharge studies. This technique uses a biased double-electrode system that enables the rate of arrival of charge carriers at the collector electrode to be determined. The electric field strength at the collector is also obtained. The action of the system is described, and its performance is compared with that predicted from electric field models with finite-element digital field computation. The measurement technique has been applied to 50 Hz corona discharges from 100 and 500 μm diameter wires at voltages of up to 30 kV r. m. s. The data have been used in conjunction with a new theoretical criterion for determining the corona extinction points on the descending quarter cycles of the alternating voltage. This has provided a complete budget of space -charge behaviour under the conditions studied, which comprises for each point-on-cycle the charge injected by the active electrode, the charge collected by the passive electrode and the space charge in the interelectrode discharge space. The method is adaptable to other geometries and to direct and impulse voltages, and to practical testing on high-voltage lines, ion sources and electrostatic precipitators.