Berylluim forms a complez with Thoron I in NH4CI- NH4OH solution at pH8-10.This complex produces a sensitive polarographic wave in this supporting electrolyte at-0.55 V. The magnitude of the current of Beryllium is proportional to its concentration from 0.05 to 0.6ppm. The interfering ions can be eliminated by addition of EDTA. This method has been applied to the determination of trace amounts of Berylluim in ores.