Universal antepartum vaginal cultures for group B streptococcus (GBS) were initiated in a Spanish hospital in 1994 using Granada medium. Infants born to carriers were monitored closely, and blood, urine and mucocutaneous areas were cultured for GBS. Group B streptococcus was detected in 543 of 4,525 women (12%). Of these, 454 gave birth vaginally, of whom 201 (44%) received intrapartum ampicillin. Prophylaxis was not administered to 253 women (56%). In this group, infants of 120 women were colonized and 1 case of neonatal GBS disease occurred. Using this protocol, most GBS carriers with risk factors received intrapartum prophylaxis. This protocol also led to early identification of colonized newborns.