Potassium-dicyclohexyl-18-crown-6 complex was used as a highly efficient carrier for the uphill transport of copper as Cu(SCN)(4)(2-) complexion through a chloroform bulk liquid membrane. By using histidine as a metal ion acceptor in the receiving phase at the optimum pH of 7.4, the amount of copper transported across the liquid membrane after 2 hours was 90.2 +/- 1.0%. The selectivity and efficiency of copper transport from aqueous solutions containing equimolar mixtures of Ag+, Cd2+, Zn2+, Ni2+, Fe2+, Co2+, Pb2+, Mn2+, Fe3+, Bi3+, and Cr3+ ions were investigated. In the presence of pyrophosphate as a suitable masking agent in the source phase, the interfering effects of Co2+, Zn2+, Pb2+, and Cd2+ ions were completely eliminated.