Consecutive newborn autopsy cases were divided into infected and noninfected groups on the basis of pathologic findings and cultures, and were compared to a concomitant consecutive group of neonatal survivors with proven bacterial sepsis. Newborns dying with bacterial infection often demonstrated leukopenia, neutropenia, and thrombocytopenia, usually associated with normal bone marrow cell production. Those with nonfatal sepsis frequently had neutrophilia with an increase in absolute band counts. Of infected newborns 80% showed one or more hematologic abnormalities as did 43% of newborns dying without bacterial infection. Of newborns dying with bacterial infection 13% had no hematologic abnormality. Blood cultures were negative in 18% (seven) of the infants dying with bacterial infection. Abnormalities of the white blood cell, differential and platelet counts are not invariably specific for bacterial infection nor do normal values adequately exclude it. Blood cultures may be negative in newborns dying with significant foci of bacterial infection.