A microwave radiometer that operates at a frequency of 3 GHz has been used on board an aircraft to determine the presence of radiation generated by corona from within both untreated control thunderstorms and thunderstorms in which 10-cm chaff was released. There was no sustained radiation recorded from the control storms. Sustained radiation was detected, however, when chaff was dispersed within thunderstorms. This indicates that chaff seeding results in the production of corona discharge that causes a discharging current to flow within the thunderstorm. For a typical example from measurements made on a relatively small, isolated thunderstorm the total current from corona intercepted by the receiving antenna beam is estimated to have been between 12 and 25 A, with a resulting current, based on a simple analysis, of 0.070--0.140 A available for discharging the thunderstorm.