Objective: To examine neutrophil counts and various neutrophil indices in preterm very low birth weight (VLBW) newborn infants (birth weight <1500g) with culture-proven late-onset sepsis to determine whether the neutrophil responses could predict the responsible infectious agent. Study design: Neutrophil parameters were examined during episodes of culture-proven sepsis in a cohort of 1026 VLBW infants, born over a 6-year period and admitted to two different neonatal intensive care units. Revised reference ranges of Mouzinho et al. for circulating neutrophil counts in VLBW infants were used to define the abnormal neutrophil indices. Results: One hundred sixty-two of 1026 (15.8%) VLBW infants had blood culture-proven late-onset infection. Infections included Gram-positive bacteria (113/162, 70%), Gram-negative bacteria (30/162, 18%) and fungi (19/162, 12%). Of the 162 sepsis episodes, only nine (5.5%) were associated with neutropenia (absolute total neutrophil (ATN) <1100/ mm3). Six of the 30 (20%) infants with Gram-negative bacterial sepsis were neutropenic compared to 2.6% infants with Gram-positive bacterial sepsis and none with fungal sepsis (odds ratio: 11; 95% confidence interval: 2.6, 47.3). Neutrophil counts and various neutrophil indices were similar in infants with late-onset Gram-positive bacterial and fungal sepsis; but total white blood cells, and ATN count were significantly lower (P=0.004 and 0.001, respectively) in infants with late-onset Gram-negative bacterial sepsis. Conclusions: In VLBW in fants, common organisms causing infection have different effects on neutrophil responses. Occurrence of neutropenia during evaluation of sepsis in sick VLBW infants is more common with Gram-negative bacterial infection.