Identification of the type and concentration of bacterial organisms in the amniotic fluid (AF) during labor might allow for earlier and more effective treatment of postpartum infections. Previous studies have identified organisms typically associated with postpartum endometritis, but the relationship to intrapartum findings has been disappointing. The purpose of this prospective study was to reassess any relationships between the bacteriology of the AF during labor and the postpartum course in the high-risk, noninfected, monitored gravid patient. The intrapartum AF bacterial flora was similar in 70 patients delivered vaginally and 80 patients delivered abdominally. In patients who did not receive prophylactic antibiotics, a total AF organism count of greater than or equal to 10(4) colonies/ml and the presence of any streptococcal or Bacteroides organism, gram-negative bacillus, or Staphylococcus aureus were significantly related to postpartum morbidity. Under these conditions, cesarean section considerably increased the risk of clinical endometritis. These results suggest that semiquantitative culture of AF obtained through the intrauterine pressure catheter prior to delivery may be of value in the postpartum management of patients delivered by cesarean section.