Anti-Vw detecting an antigen on Miltenberger I (Mi I) variant glycophorin A (GPA) has rarely been reported as a cause of hemolytic disease of the newborn (HDN). We report an infant with severe HDN due to anti-Vw. Examination of the Vw+ erythrocytes of the father and paternal grandmother by sodium dodecylsulphate polyacrylamide gel electrophoresis showed an extra trypsin-sensitive, periodic-acid-Schiff staining band, consistent with Mi I variant GPA. Staining of Western blots by monoclonal antibodies showed that normal paternal GPA expressed blood group M, while Mi I variant GPA expressed blood group N. Mi I variant GPA expressed the trypsin-sensitive antigenic determinant detected by MoAb 10F7, indicating that the alterations known to occur in the trypsin-sensitive fragment of Mi I variant GPA do not affect expression of the antigen detected by 10F7.