The purpose of this study was to investigate the effect of severe “stress” on neonatal neutrophil (PMN) phagocytosis, and to compare the ability of neonatal and adult PMNs to ingest [3H]-labeled type Ic group B streptococcus (GBS). Three patient populations were studied: healthy and “stressed” newborn infants and healthy adults. Severe “stress” was defined as an acute, noninfectious respiratory illness, sepsis or severe birth asphyxia; 94% of these infants required assisted ventilation. Radiolabeled GBS was opsonized with 5% adult serum, and incubated with PMN monolayers adherent to glass coverslips. Bacterial uptake was determined at 0, 40, 60, and 80 min and expressed as counts per min/106PMNs. Neutrophis from healthy and “stressed” newborn infants demonstrated a significant increase in bacterial uptake with time. Adult controls also showed a significant increase in phagocytosis through 60 min, but not during the 60–80 min time period. PMNs from “stressed” and healthy infants demonstrated enhanced bacterial uptake when compared to adults at 40, 60, and 80 min. There were no significant differences in bacterial ingestion between “stressed” and healthy infants. Radiolabeled GBS uptake did not correlate with birth weight, study age, Apgar scores, or peripheral leukocyte count for the “stressed” newborn population. Neutrophils from healthy and “stressed” newborn infants thus demonstrate increased phagocytosis of GBS when compared to healthy adults.