The finding that En(a ‐) red blood cells are Wr(a‐b‐), and thus probably represent a “null” phenotype of the Wright system, has provided evidence of the independence of the Wright blood group system from many others. Detection of blood group antigens on “null” red blood cells almost certainly indicates that those antigens do not belong to the same blood group system as the “null” cells. In the case of Wright, lack of certainty that En(a ‐) is the “real,” or only, null type slightly reduces the