Simultaneous measurement of ELF emissions and bremsstrahlung X rays were made by using a balloon borne experiment flow from Fairbands, Alaska, on September 30, 1976. Several intense auroral X ray bursts of 2--3 minute duration were detected that have been interpreted to be the result of relativistic electron precipitation (REP). Simultaneously, the intense of ELP emissions increased and was also observed to have periodicities similar to those in the X ray flux. These combined measurements are evidence of magnetosphric wave-particle processes contributing to electron precipitation. The presence of pulsations in the precipitating flux is the only report of this nature during relativistic precipitation. The data have been compared with precipitation and modulation theories, and we note that the data agree with a model in which ULF modulation of the emission growth rate occurs. It is posulated that this REP event resulted from ELF wave and electron interaction, possibly triggered by the ULF occurrence rather than directly by ULF electron interactions.