The facilitated transport of carbon monoxide through thin, immobilized films of cuprous chloride solutions is investigated, using a tracer C14O technique. Steady-state tracer flux measurements are used to determine the second-order forward rate constant and equilibrium constant for the reversible reaction of CO with cuprous ion. The enchanced results at low CO partial pressures can be interpreted in terms of a consecutive reaction model. The cuprous ion is remarkably effective as a carrier for CO. The CO permeation rate in the presence of cuprous ion can be increased by two orders of magnitude over the nonfacilitated flux. As such, the cuprous ion is an attractive facilitating agent for use in a membrane separation system.