This work presents a new envisioned application of carbon molecular sieve membranes technology. It proposed the on-line recycling of xenon in anaesthetic closed re-breathing circuits. The cost and rarity of the so-called ideal anaesthetic gas xenon have impaired its widespread use in clinical practice. Reducing its waste through recycling will help xenon to find its place among anaesthetic substances. In collaboration with the only two companies worldwide that ever produced carbon molecular sieve membranes, several samples were selected and tested for xenon recovery from a,as mixture containing carbon dioxide and nitrogen. Mono- and multicomponent permeation experiments were performed with the most promising membranes. Very high ideal selectivities CO,/Xe and N-2/Xe were obtained in combination with high permeabilities. Multicomponent permeation results suffered from pore blocking effects of xenon. Multicomponent permeabilities were used to simulate a membrane module separation unit for recycling anaesthetic xenon. Simulation results indicate that xenon recovery above 97% can be achieved. (c) 2007 Elsevier B.V. All rights reserved.