Objective: To study the effects of continuous morphine infusion on arterial bl ood pressure in ventilated neonates. Design: Blinded randomised placebo controll ed trial. Setting: Level III neonatal intensive care unit in two centres. Patients: A total of 144 ventilated neonates. Inclusion criteria were postnatal age < 3 days, ventilation < 8 hours, and indwelling arterial line. Exclusion criteria were severe asphyxia, severe intraventricular haemorrhage, major congenital anomalies, neu romuscular blockers. Intervention: Arterial blood pressure was measured before t he start and during the first 48 hours of masked infusion of drug (morphine/plac ebo; 100 μg/kg+10 μg/kg/h). Outcome measures: Arterial blood pressure and blo od pressure variability. Results: There were no significant differences in overa ll mean arterial blood pressure between the morphine group (median (interquartil e range) 36 mm Hg (6) and the placebo group (38 mm Hg (6)) (P=0.11). Although si gnificantly more morphine treated patients (70%) showed hypotension than the pl acebo group (47%) (P=0.004), the use of volume expanders and vasopressor drugs was not significantly different (morphine group, 44%; placebo group, 48%; P=0. 87), indicating the limited clinical significance of this side effect. Blood pre ssure variability was not influenced by routine morphine analgesia (P=0.81) or a dditional morphine (P=0.80). Patients with and without intraventricular haemorrh age showed no differences in blood pressure (Mann-Whitney U test 1953; P=0.14) or incidence of hypotension (χ2 test 1.16; df 1; P=0.28). Conclusions: Overall arterial blood pressure, use of inotropes, and blood pressure variability were n ot influenced by morphine infusion. Therefore the clinical impact of hypotension as a side effect of low dosemorphine treatment in neonates is negligible. Objective: To study the effects of continuous morphine infusion on arterial blodropress in ventilated neonates. Design: Blinded randomized placebo controll ed trial. Setting: Level III neonatal intensive care unit in two centers. Patients: A total of 144 ventilated neonates. Inclusion criteria were postnatal age <3 days, ventilation <8 hours, and indwelling arterial line. Exclusion criteria were severe asphyxia, severe intraventricular haemorrhage, major congenital anomalies, neu romuscular blockers. Intervention: Arterial blood pressure was measured before t he start and during the first 48 hours of masked infusion of drug (morphine / plac ebo; 100 μg / kg + 10 μg / kg / h) Outcome measures: Arterial blood pressure and blo od pressure variability. arterial blood pressure between the morphine group (median (interquartile range) 36 mm Hg (6) and the placebo group (38 mm Hg (6)) (P = 0.11). Although si gnificantly more morphin The use of volume expanders and vasopressor drugs was not significantly different (morphine group, 44%; placebo group, 48%; P (70%) showed hypotension than the pl acebo group = 0.87), indicating the limited clinical significance of this side effect. Blood pre ssure variability was not influenced by routine morphine analgesia (P = 0.81) or a dditional morphine (P = 0.80). Patients with and without intraventricular haemorrhosis showed no differences in blood pressure (Mann-Whitney U test 1953; P = 0.14) or incidence of hypotension (χ2 test 1.16; df 1; P = 0.28). Conclusions: Overall arterial blood pressure, use of inotropes, and blood pressure variability were n ot influenced by morphine infusion. Therefore the clinical impact of hypotension as a side effect of low dosemorphine treatment in neonates is negligible.