Intra-arterial blood pressure measurements recorded during the first week of life in 32 stable very low birth weight infants (20 of birth weight up to 1250 g and 12 with birth weight 1251-1500 g) were reviewed. None of the infants received inotropic drugs or were given infusions of colloids to manipulate the blood pressure during the periods from which the recordings were taken. The mean systolic, mean and diastolic blood pressure measurements for infants of birth weight greater than 1250 g were significantly higher than those recorded in the infants of birth weight of up to 1250 g (figure 1). The mean blood pressure (calculated by adding one third of the pulse pressure to the diastolic pressure) in the larger infants showed a significant increase with increasing postnatal age, but this increase was not apparent in the smaller infants (figure 2). Figure 3 shows the range of systolic, mean and diastolic blood pressure values that were recorded. The mean values were remarkably constant with diastolic blood pressure varying between 31 and 34 mmHg, mean blood pressure between 35 mmHg and 40 mmHg, and systolic blood pressure between 46 mmHg and 52 mmHg. Intra-arterial lines provide a convenient and accurate route for blood pressure monitoring. It is important that a normal range of blood pressure values in the very low birth weight infant is established so that hypotension, with the potential risk of cerebral ischemia, can be avoided.