The usefulness of the differential white blood cell count in distinguishing early-onset group B streptococcal disease from other causes of neonatal respiratory distress was studied in 45 infants with culture-proved infection. The initial diagnosis was hyaline membrane disease in 19 infants, wet lung syndrome 13, and other causes of respiratory distress in 13. Thirty-nine (87%) had abnormal absolute neutrophil counts, 25 with neutropenia and 14 with neutrophilia. The absolute immature neutrophil count was elevated in 19 infants (42%). Forty-one infants (91%) had an abnormal immature neutrophil to total neutrophil ratio. All infected infants were identified when both the absolute total neutrophil count and ratio were used. The differential white cell count appears to be a useful tool for screening infants presenting with respiratory distress in the first 48 hours of life and for separating early-onset group B streptococcal disease from other causes of neonatal respiratory distress.