During 23 exchange transfusions, the granulocytes from 27 donors and 16 newborn infants were tested for opsonic activity and granulocyte function by the nitrobluetetrazolium test. Granulocyte function in a newborn baby receiving an exchange transfusion can be altered positively or negatively, depending on the quality of the donor's blood. If exchange transfusion is used in the management of neonatal sepsis, special attention should be given to the immunological properties of the donor blood.