The neonatal and obstetric approaches to preventing group B streptococcal neonatal infections are reviewed. Although recent reports recommend prophylactic antibiotic treatment of antepartum and intrapartum group B streptococcal carriers and low-birth-weight infants, acceptance of these schemes is not widespread. A preliminary study to evaluate the value of semiquantitative vaginal and cervical cultures of antepartum women for group B streptococcus in predicting maternal and neonatal infectious morbidity revealed: 1) 11% of the study population were carriers (group B streptococcus isolated from broth only) but only 2.8% had heavy colonization (growth in broth and on streaked plates), and 2) morbidity associated with 8 heavily colonized mothers during the current pregnancy included group B streptococcal endometritis (1 patient), neonatal sepsis (1), and readmission of a newborn for transient cyanosis (1). Two of the heavily colonized mothers were known carriers in their last pregnancy; 1 had group B streptococcal endometritis and the infant of the second developed clinical sepsis at 2 weeks of age. The clinical value of semiquantitative culture techniques requires additional investigation.