Leukocytic infiltration was found in 10% of the umbilical cords examined in a preliminary study. The present examination of the cords obtained from 1,000 consecutive deliveries made it possible to correlate the presence or absence of the infiltration with each of a list of maternal and fetal factors. Lymphocytic infiltration of the umbilical cord was most strongly associated with prolonged labor, with a staining of the amniotic fluid by meconium, and with positional abnormalities of the cord. Correlations with inhalation anesthesia, with multiparity, and with fetal tachycardia or bradycardia were suggestive but weaker. Leukocytic infiltration of the cord is therefore interpreted to mean that there has been fetal distress and anoxia due to hindrance of the umbilical circulation.