Communication: Anions can be selectively transported across a bulk liquid membrane by the 1-hexadecylferrocenium ion through a process driven by a chemically generated redox potential gradient. The liquid membrane, a solution in dichloromethane, acts as a filter for anions, being permeable to perchlorate ions and impermeable to choride ions. The alkyl substitution of the ferrocenium ion serves to confine the ion to the membrane phase.