OBJECTIVE Our purpose was to determine whether tumor necrosis factor-alpha, interleukin-6, and fetal fibronectin could be identified in the lower genital tract during pregnancy and whether their occurrence was associated with preterm delivery. METHODS A prospective cohort study was undertaken of 111 pregnant women in which cervicovaginal swabs were obtained at < 37 weeks' gestation. Seventy-three specimens were obtained from women during routine prenatal examination, whereas 38 specimens were obtained from women undergoing evaluation of preterm labor. Interleukin-6 and fetal fibronectin levels were determined by enzyme-linked immunosorbent assays, whereas tumor necrosis factor-alpha determinations were by bioassay. Urinary tract and lower genital tract samples were cultured for evidence of infection. The rates of maternal and neonatal complications were assessed. RESULTS In patients undergoing evaluation for preterm labor the presence of tumor necrosis factor-alpha or fetal fibronectin was associated with an increased prevalence of preterm delivery. Women with tumor necrosis factor-alpha had a 6.19 greater risk (p < 0.005), whereas the presence of fetal fibronectin was associated with a 4.81 greater risk (p < 0.05), of preterm birth. This association was not evident in women who were sampled during routine prenatal examinations. In all women the presence of cytokines in the lower genital tract correlated with detection of fetal fibronectin. CONCLUSIONS Localized inflammatory responses may lead to microscopic disruption in the amniotic membranes, leading to leakage of fibronectin. In patients being evaluated for preterm labor, the presence of tumor necrosis factor-alpha or fetal fibronectin in the lower genital tract is predictive of subsequent preterm delivery.