Modification of an anion-exchange membrane by (1-(2-arsono-phenylazo))-2-hydroxy-3,6-naphthalenedisulfonic acid (thoron) results in a membrane that can chelate metals. The high affinity of the disulfonate for the anion-exchange sites together with molecular adsorption of the aromatic thoron onto the polymers yields a system that is stable in strong acids at or below 1 M. By employing a relatively high pH sample (5-9) in conjunction with an acidic stripping solution (0.2 - 1.0 M HCl), uphill transport of Cu(II) and Zn(II) was accomplished. The transport rate was increased by means (lower chelating capacity and the use of a chelate-forming aid on in the stripping solution) of promoting the volume diffusion mechanism of membrane transport. With a 0.05 mmol per dry gram chelating capacity and a 0.1 M EDTA stripping solution (pH 6.5), an enrichment factor of 16 was observed in a one-hour experiment with a 200 mL sample, 11 cm2membrane, and 5 mL stripping solution. This value compares favorably with those obtained by other uphill transport modes under the same conditions.