The behavior of a monocyclic polyether (crown ether) and a bicyclic polyether (cryptand) towards liquid-liquid extraction and facilitated cotransport of silver, copper, and zinc was investigated. It was shown that, with regard to their structure, the relative size of their macrocycle cavities, and the nature of the inserted ion, considerably influences the efficiency of the extraction and the cotransport. On the other hand, this study also revealed the formation of emulsions in the monocyclic polyether organic phase that constitute a barrier for the carrier-metal complex formation in the membrane support. An impregnation time of 1 hr of the support in the organic phase is necessary to achieve good efficiency for the supported liquid membrane (SLM). The optimum of the other undamental parameters (polyether concentration, metal concentration, and support characteristics) were determined.