Mapharsen has recently become a favorite drug in the treatment of syphilis and is replacing other arsenical compounds in many clinics. Among many papers on its properties and effectiveness, probably the most comprehensive are those of Gruhzit and Dixon1 and Cole and Palmer.2 It is generally regarded as a safer drug than arsphenamine or neoarsphenamine. Stephenson and Wingo3 reported that 12,860 doses of mapharsen were given in the United States Navy between Jan. 1, 1935 and Dec. 31, 1937, with only 1 serious reaction. This reaction was in a case in which neoarsphenamine had caused an exfoliative dermatitis. Ten years later a single dose of mapharsen caused a recurrence, from which the patient recovered after twenty-four days in the hospital. In contrast to this record of no deaths and only 1 serious reaction following 12,860 doses of mapharsen is the report by the same author of a