This document specifies a procedure for the determination of hydrochloric acid (gastric acid concentration) extractable inorganic arsenic in seaweed. Collaborative studies have been carried out (Annex A). The method is suitable for the determination of inorganic arsenic not less than 1 mg/kg and below 100 mg/kg on a dry weight basis. The amount of inorganic arsenic is considered to be that part determined by the procedure described in this document.