A standard chart of symphysial-fundal height from 20 to 40 weeks of pregnancy was derived from measurements in 103 women who were delivered of infants weighing between the 25th and 90th centile for gestation. The chart was used to predict birth weight in a group of 138 high-risk patients. Thirty (73.1 per cent) of 41 infants with birth weight for gestation less than 10th centile could be detected by this one clinical measurement. A single measurement was most accurate for detecting low birth weight for gestation at 32 to 33 weeks. It is suggested that symphysial-fundal height measurements should be made routinely on all antenatal patients and that each obstetric unit should derive its own standard curves.