Definition THERE is a difference of opinion among medical writers as to what constitutes the Guillain-Barré syndrome. Regardless of their country of origin, most authors fall either into French or Anglo-American groups which disagree as to the nomenclature, clinical findings, and laboratory data of the neurological disease under consideration. Mésentente Cordiale. —Misunderstanding due to errors in translation aggravate a semantic controversy which was already in evidence at the time of World War I, when several cases of motor and sensory paralysis were observed among the troops fighting in France. Guillain, Barré, and Strohl,1 who reported the cerebrospinal fluid and electromyographic findings on two cases of "radiculoneuritis" observed in French soldiers, thought the illness they described to be a new entity, of toxic or infectious origin. On the other hand Holmes,2 Bradford,3 Casamajor,4 and Kennedy,5 reporting independently their observations in British troops, agreed that they were all discussing the same illness,