Four hundred thirty-one parturient women were tested for cervical infection with group B streptococcus using standard bacterial culture and a commercially available latex particle agglutination test. The total time required to perform each latex test was 30 minutes or less. The prevalence of endocervical group B streptococcus by culture was 4.4%, half of whom developed clinically significant group B streptococcus infection; all such cases were identified correctly by the latex test. The predictive value of a negative latex test for a negative group B streptococcus culture was 98%. This method seems promising as a rapid intrapartum diagnostic test for ruling out group B streptococcus infection and thus avoiding unnecessary antibiotic treatment.