The separation of uranium from synthetic Hanford site groundwater by liquid-liquid extraction and by supported liquid membranes (SLM) was atudied. Bis(2,4,4-trimethylpentyl) phosphinic acid, H[DTMPeP], contained in the commercial extractant Cysnex 272, was selected for the membrane carrier because of its selectivity for uranium over calcium and magnesium. n-Dodecane was used as diluent and polypropylene membranea were used as the support. A water soluble complexing agent, 1-hydroxyethane-1,1-diphoaphonic acid, HEDPA, was used as atrlpping agent.