Support for the existence of an immunoneutropenia of the neonatal period was not obtained. The leukocyte counts of 39 full-weight newborn infants who stimulated their mothers to form leukoagglutinins were compared with the counts of 76 newborns who failed to stimulate formation of these agglutinins. A significant difference between the mean total leukocyte or differential counts for the two groups was not observed. The leukocyte counts of both groups throughout the first four days of life were in close agreement with the accepted values for this period. The platelet counts for 10 full-weight newborn infants who stimulated white cell agglutinin formation did not differ over the first four days of life from a control group of 37 newborns. Transplacental passage of the leukocyte agglutinins was demonstrated in 15 of 49 newborns examined. Persistence of antibody in the serum of the newborn was variable It was concluded that in this series transplacental passage of leukocyte agglutinins from sensitized mothers to newborns with antigen did not induce significant leukopenia or neutropenia.