The Association of Anaesthetists of Great Britain and Ireland (AAGBI) guideline "Checking Anaesthetic Equipment 2012" recommends testing the anaesthetic breathing system for occlusions and leaks using the 'two-bag' test before each case. This requires a second reservoir bag which should be marked 'TEST BAG'. This bag has been produced for that reason and one should be kept with every anaesthetic machine for the 'two-bag' test procedure.