In a DRRR Proficiency Testing (PT RVEP 0970) both methods, the IFU 7a as well as the HPLC–IMER (and three other methods for sulfite analysis2), were subjected to an ability test. 24 laboratories located within Europe were involved in total. The IFU 7a was per-formed by 16 laboratories, the HPLC–IMER by 5 laboratories. The reference material was an industrially produced red grape juice.