Abstract 68 of a group of 2745 consecutive pregnant women had group B streptococci in their urine. In this group primary rupture of the membranes and premature delivery occurred in 35% and 20% respectively. In women without group B streptococci 15% had primary rupture of the membranes and premature delivery occurred in 8·5%. Group B streptococcal sepsis occurred in five infants, all had mothers with positive urine culture. Women with group B streptococci in their urine seem to have a significantly increased risk of primary rupture of the fetal membranes and premature delivery.