Vaginal colonisation of pregnant women with group B streptococci (GBS) was not related to age, parity or blood group. There were marked differences between racial groups, Asians having a low colonisation rate and Negroes a high rate. Vaginal GBS colonisation was associated with intrapartum pyrexia, but not with preterm labour, premature rupture of membranes or other complications in labour. Group B streptococci may be an important cause of bacteriuria in pregnancy and their effect on the outcome of pregnancy as urinary pathogens needs further evaluation.