This is a study of group B Streptococcus during labor of 121 patients in whom group B Streptococcus was isolated in the vagina and/or rectum before delivery. The intrapartum vaginal culture was positive in 55.2% of the antepartum carriers (32/58). When the vaginal culture during delivery was positive, the group B Streptococcus was isolated in the amniotic fluid 2 h after the rupture of membranes in 81% of the cases. The newborns of antepartum carriers, when the labor developed naturally, were colonized by group B Streptococcus in 69.2% of cases when the intrapartum vaginal and/or amniotic fluid cultures were positive (9/13), while only 5.6% of the newborns of antepartum carriers but with negative cultures during delivery were colonized by group B Streptococcus (1/18). The most frequent positive neonatal culture was in the umbilicus (83.3%) followed by the external ear (62.5%).