This study appears to be the first to report xenon as a furin inhibitor. The observed inhibition continued throughout the duration of the experiment. Since no enzyme activity was measured for 24 hours after xenon exposure, although the enzyme and substrate were both present, the effect of xenon lasted at least this long, although perhaps it would have lasted longer if the experiment had been continued. The effectiveness of xenon as a furin inhibitor, its favorable side-effect profile, and its long history of safe anesthetic use when used under direct medical supervision, make it a promising treatment for the viral, bacterial, neoplastic, and other diseases facilitated by furin or its substrates. Further studies using xenon in cell culture or in clinical trials may clarify its clinical role for such diseases.