Inhalation of carbon dioxide (hypoxia) commonly is used as a method of euthanasia in the United States. Although euthanasia by carbon dioxide has been the accepted method of choice in laboratory settings for the past 2 decades, it
recently has been shown that some species display a high degree of avoidance of concentrations of carbon dioxide (Leach et al. 2002) because of irritation of mucosal linings. Alternatively, argon gas has been used in the European Union for laboratory mice (M. musculus). Euthanasia techniques are reviewed and approved by the IACUC during review of the animal care and use protocol. Investigators should be aware that animal welfare regulations urge following the most current AVMA Panel of Euthanasia report (AVMA 2001) and that deviations from these guidelines must be justified. Justification for deviations can include citation of published literature or results from pilot studies.