A given mixture of dibenzodiaza-15-crown-4 and oleic acid was found to be a highly efficient and selective cooperative carrier for uphill transport of Cu(II) ions through a chloroform liquid membrane. In the presence of L-cysteine as a suitable stripping agent in the receiving phase, the amount of copper transported across the liquid membrane after 120 min is 94.7+/-0.8%. The selectivity and efficiency of Cu2+ transport from aqueous solutions containing other cations such as Li+, K+, Ag+, Tl+, Ca2+, Sr2+, Co2+, Ni2+, Zn2+, Pb2+, Cd2+ and Hg2+ ions were investigated. The interfering effect of Cd2+ and Pb2+ ions was considerably diminished in the presence of ammonium acetate as a proper masking agent in the source phase.