To test the in vivo effect of amniotic fluid on endocervical microflora, we performed endocervical cultures before and after rupture of the membranes in 20 patients in term labor. There were no significant qualitative or quantitative differences in aerobic or anaerobic isolates for up to 4 hours after membrane rupture. Group B streptococci, isolated in two patients (10%), persisted after rupture of the membranes. These data suggest that endocervical cultures are minimally influenced by rupture of the chorioamnion for at least 4 hours.