A control and an x-ray detector were flown into thunderstorms in 1984. The x-ray detector found statistically significant radiation flux increases in the energy range 5 to >110 keV for time intervals of several seconds each. Simultaneously the control detector showed no statistically significant changes. The x-ray flux is sometimes seen to increase prior to observed lightning discharges and then return to background levels within 0.1 seconds of a lightning flash initiation. The temporal development of these x-ray bursts is discussed and related to inferring the scale size of the x-ray emitting regions.