A system has been developed for the evaluation of hematological data in the newborn. Normal values were established for segmented (neutrophil) and nonsegmented (band) polymorphonuclear leukocytes in the peripheral blood of 169 healthy full-term infants during the first five days of life. This normal data is displayed graphically and the values for infants under study are compared directly. Newborn infants with proven bacterial infections had normal neutrophil counts; however, the band counts increased significantly beyond the normal range. Therefore, the simple laboratory procedure for ennumerating band neutrophils with comparison of absolute values and changes to a normal range represents a hematologic technique of major importance in the diagnosis of sepsis of the newborn infant.