“…Early studies on the immunologic characteristics of Hp did not reveal differences among the three phenotypes, or between free and Hb-bound Hp (5,6). Recently, however, with the use of more discriminating antiReceived for publication 2 May 1968. sera both these categories of antigenic differences have been demonstrated by Korngold (7,8) and by Eichmann, Deicher, and Cleve (9). The latter group has proposed the following terminology: (A) represents the antigenic determinant present in all common Hp types and in their Hb complexes.…”