To determine the role of polymorphonuclear (PMN) leukocyte transfusions in neonates with sepsis, 23 consecutive newborns were prospectively randomly selected during an 18-month period in a treatment plan to receive polymorphonuclear leukocyte transfusions with supportive care or supportive care alone. Thirteen neonates received transfusions every 12 hours for a total of five transfusions. Each transfusion consisting of 15 mL/kg of polymorphonuclear leukocytes was subjected to 1,500 rads of radiation. The polymorphonuclear leukocytes were obtained by continuous-flow centrifugation leukapheresis and contained 0.5 to 1.0 X 10(9) granulocytes per 15 mL with less than 10% lymphocytes. Pretreatment demographic, clinical, and laboratory variables that were found to be insignificant in prognosis between newborns who received transfusions and newborns who did not receive transfusions included weight, gestational and postnatal age, hypoxia, acidosis, hypotension, initial absolute granulocyte count (AGC), initial levels of immunoglobulins (IgA, IgG, and IgM), and total hemolytic complement. Positive findings on blood cultures were obtained in 14/23 patients and seven were randomly selected for each treatment group. Absolute granulocyte counts were less than 1,500/microL in 13 patients but tibial bone marrow examinations revealed that the neutrophil supply pool was depleted in only three patients. The survival was significantly greater in the treatment group (13/13, 100%) compared with the group that did not receive transfusions (6/10, 60%, P less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)