The history of a family with three cases of neonatal neutropenia is reported. During the mother’s last pregnancy leukocyte antibody titers were found to be rising, culminating in a titer of 1:512 at delivery, when leukolysins and passive transfer of antibody to the fetus in the cord blood were also demonstrated. This pregnancy resulted in an infant with a severe degree of neutropenia during its neonatal period. The original sensitization was attributed to prior transfusion with the husband’s whole fresh blood. The whole process can be compared with the sensitization produced by the Rh factors.