I wondered about that same question a while ago when ferret was dying and the only vet hospital that will do ferrets in the middle of the night is a half hour away. So I Googled for information. The best answer was from a rattery right here near Tucson that has detailed information about making a carbon dioxide filled chamber and using simple baking soda and vinegar to provide the gas. There is a proper way to do it so the animal isn't frightened but slowly goes into a stupor before the lethal concentration is given. The directions were for an animal up to two pounds. I have never had to use this method yet but some times I am tempted when I know a ferret is on the way to the Rainbow Bridge. Then I have to drive 25 miles to our vet, pay for the euthanasia and drive home again. This would be much less costly. Carol Owens Ferret Friends, Inc. Tucson AZ [Posted in FML 6333]