The stability of enflurane in soda lime was examined. A product of enflurane decomposition was detected after the reaction of enflurane with soda lime, but not in the absence of soda lime. The production of this compound, identified as 1-chloro-1,2-difluorovinyl difluoromethyl ether by gas chromatography-mass spectrometry, increased with time and temperature. The same decomposition product was produced by the reaction of enflurane with potassium, sodium, or calcium hydroxides, and it was also detected in the gas phase at a maximum concentration of 1.29 ppm at 420 min after 5% enflurane circulated with 200 ml/min carbon dioxide gas in a closed anesthesia circle system with a soda lime canister and a model lung. We concluded that enflurane was decomposed to 1-chloro-1,2-difluorovinyl difluoromethyl ether by soda lime.