Prematurity remains a major cause of perinatal mortality in the United States. Some research has indicated that infectious agents play a role in either initiating preterm labor, causing premature rupture of the membranes, or preventing tocolysis. This study attempted to determine if the presence of various vaginal pathogens in early pregnancy was associated with the subsequent development of premature rupture of membranes or preterm labor. We found that among 233 evaluable patients those with Trichomonas vaginalis were significantly more likely to have premature rupture of the membranes (p less than 0.03), and those with Bacteroides sp. were more likely to be delivered of their infants before 37 weeks (p less than 0.03) and to have infants weighing less than 2500 gm (p less than 0.05). Those with Ureaplasma urealyticum more frequently began preterm labor (p less than 0.05). Preterm premature rupture of the membranes was found significantly more often among patients with Bacteroides sp. Stepwise multiple logistic regression analysis indicated that those associations were not related to the number of previous abortions, deliveries, or preterm deliveries or to maternal age. We conclude that microbiologic screening in early pregnancy may aid in the assessment of patient risk for preterm delivery.