Maternal and neonatal white blood cell counts, neonatal pharyngeal culture, and histologic examination of placenta were done in 55 term pregnancies with premature rupture of fetal membranes (PROM) and in 52 term pregnancies without PROM to study the correlation between placental inflammation and clinical outcome. The results were as follows: (1) A higher rate of chorionitis and chorionic plate inflammation exist in patients with PROM. The inflammation rate of chorionic plate was 90% in patients with labor lasting longer than 12 hours, and only 38% in patients with a duration less than 12 hours. The difference was highly significant (P less than 0.01). (2) The positive rate of neonatal pharyngeal culture was higher in the PROM group than that in the control group (P less than 0.01). (3) Inflammation of chorionic plate was seen in 6/6 of the cases with neonatal infection. The corresponding rate was only 38% in cases without neonatal infection (P less than 0.01). It is suggested that in patients with PROM, efforts should be made to shorten the time of labor and the neonates should be watched for possible infections in the presence of inflammation of the placenta, particularly the chorionic plate.