Urine oestriol values from 327 pregnancies with antenatal complications were measured between 30 weeks gestation and term. Mean values were much lower than those obtained from pregnancies without complications. When infants were light for dates or developed evidence of neonatal morbidity, oestriol values were more likely to have been below the normal range than in pregnancies resulting in deliveries of normal infants. There was no evidence of severe fetal jeopardy in most pregnancies with oestriol values below normal. Perinatal death was consistently predicted when urine oestriol values lay below a line joining 35 mumol/day at 30 weeks and 65 mumol/day at term.