[en] The differential polarographic behaviour of molybdenum(VI) and uranium(VI) was studied in organic solutions derived from trioctylphosphine oxide (TOPO)-cyclohexane extracts. The extraction of molybdenum(VI) and uranium(VI) was carried out in 4 M HCl media using 0.1 M TOPO-cyclohexane. The organic solution for polarographic investigation was composed of 0.1 M TOPO, cyclohexane, ethanol and HNO₃. The separation of the uranium and molybdenum polarographic peaks was studied as a function of increasing concentration of the supporting electrolyte (HNO₃). The molybdenum and uranium contents of the ore lixiviation solution were determined. The results of studies of the effects of possible interference are included. (Auth.)