A bacteriological study of 10,962 vaginal swabs has made it possible to work out the percentage of women who are carriers of Group B streptococci in their vaginas. The count varies between 9.43 and 17.25 per cent according to the different populations that were studied. Serotyping of the strains of 1,030 vaginal specimens was carried out and it was found that serotypes II and III predominated. We have been able to study 27 strains responsible for infection in the early neonatal period such as septicaemia or meningitis at the same time as we were studying the vaginal flora. The distribution of the serotypes illustrates a predominance of types 1c and III in 70 per cent of cases. Contamination between the mother and the child is obvious but in 95 per cent of cases the strain isolated in the infected child was of the same serotype as that which was isolated in the mother. Group B streptococci are still very sensitive to antibiotics and particularly to the penicillins. It does seem to us to be unrealistic to treat with antibiotics prophylactically in pregnancy. On the other hand careful attention to the newborn and careful bacteriological study of multiple specimens taken from the skin and the orifices gives easy screening for the germ and the possibility of treating infants that are grossly contaminated.