Arterial pressure (AP) (systolic, mean and diastolic) was recorded during the first 72 hours of life in 93 neonates, 27 to 42 weeks of gestational age and weighing 800 to 4,600 g, i.e. in stable hemodynamic and respiratory conditions. 4,464 measurements were performed. Results show that the 3 AP parameters increase with gestational age and birth weight and that AP increases with age after birth in full term as well as premature children. The physiologic variability of AP in full term and premature children accounts for the difficulty of establishing standards and for the need of a permanent recording of this parameter.