1. Systolic blood pressure was measured by a Doppler ultrasound technique in twenty normal babies on 6 successive days after the day of delivery. In three babies blood pressure was recorded every 15 min for 24 h.
2. Systolic blood pressure during the first 6 days of life was 95 (sem = 2) mmHg.
3. Systolic blood pressure increased on average by 2 mmHg/day, but increased most between the second and third days of life.
4. Systolic blood pressure was 11 mmHg higher when awake than when the babies were asleep.
5. There was marked within-baby variation in the systolic blood pressure of neonates, which could not be accounted for by age or recognizable changes in level of consciousness.