Arsenicals have been used since ancient Greek and Roman civilizations and in the Far East as part of traditional Chinese medicine. In Western countries, they became a therapeutic mainstay for various ailments and malignancies in the 19th and early 20th centuries. Fowler's potassium bicarbonate-based solution of arsenic trioxide (As2O3)solution was the main treatment of chronic myeloid leukaemia until the 1930s. After a decline in the use of arsenic during the mid-20th century, arsenic trioxide was reintroduced as an anticancer agent after reports emerged from China of the success of an arsenic trioxide-containing herbal mixture for the treatment of acute promyelocytic leukaemia. Arsenic trioxide was first purified and used in controlled studies in China in the 1970s.Subsequently, randomised clinical trials performed in the United States led to FDA approval of arsenic trioxide in the treatment of patients with relapsed or refractory acute promyelocytic leukaemia.