Objectives: To determine the effects of continuous morphine infusion in ventil ated newborns on plasma concentrations of adrenaline (epinephrine) and noradrena line (norepinephrine)-and their relation to clinical outcome. Design: Blinded, randomised, placebo controlled trial. Setting: Level III neonatal intensive care units in two centres. Patients: A total of 126 ventilated neonates (inclusion c riteria: postnatal age < 3 days, duration of ventilation < 8 hours, indwelling a rterial catheter for clinical purposes; exclusion criteria: severe asphyxia, sev ere intraventricular haemorrhage, major congenital anomalies, neuromuscular bloc kers). Interventions: Plasma adrenaline and noradrenaline concentrations were de termined in patients during blinded morphine (n = 60) and placebo (n = 66) infus ion (100 μg/kg plus 10 μg/kg/h). Results: Plasma concentrations at baseline (n mol/l with interquartile range in parentheses) were comparable in infants treate d with morphine (adrenaline, 0.22 (0.31); noradrenaline, 2.52 (2.99)) or pla cebo (adrenaline, 0.29 (0.46); noradrenaline, 2.44 (3.14)). During infusion, median adrenaline concentrations were 0.12 (0.28) and 0.18 (0.35)-and medi an noradrenaline concentrations were 2.8 (3.7) and 3.8 (4.0) for the morphin e and placebo treated infants respectively. Multivariate analyses showed that no radrenaline (p = 0.029), but not adrenaline (p = 0.18), concentrations were si gnificantly lower in the morphine group than the placebo group. Furthermore, nor adrenaline concentrations were related to the length of stay in the neonatal int ensive care unit. Conclusions: Continuous morphine infusion significantly decrea sed plasma noradrenaline concentrations in ventilated newborns compared with pla cebo treatment. The results of this study support the idea that routine morphine administration decreases stress responses in ventilated neonates. Objectives: To determine the effects of continuous morphine infusion in ventil ated newborns on plasma concentrations of adrenaline (epinephrine) and noradrena line (norepinephrine) -and their relation to clinical outcome. Design: Blinded, randomized, placebo controlled trial. neonatal intensive care units in two centers. Patients: A total of 126 ventilated neonates (inclusion c riteria: postnatal age <3 days, duration of ventilation <8 hours, indwelling a rterial catheter for clinical purposes; exclusion criteria: severe asphyxia, sev ere intraventricular haemorrhage, major congenital anomalies, neuromuscular bloc kers). Interventions: Plasma adrenaline and noradrenaline concentrations were de termined in patients during blinded morphine (n = 60) and placebo (n = 66) infus ion kg / h). Results: Plasma concentrations at baseline (n mol / l with interquartile range in parentheses) were comparable in infants treate d with morphine (adrenaline, 0.22 (0.31); noradrenaline, 2.52 (2.99)) or pla cebo (adrenaline, 0.29 (0.46); noradrenaline, 2.44 (3.14)). During infusion, median adrenaline concentrations were 0.12 (0.28) and 0.18 Noradrenaline concentrations were 2.8 (3.7) and 3.8 (4.0) for the morphin e and placebo treated infants respectively. Multivariate analyzes showed that no radrenaline (p = 0.029), but not adrenaline (p = 0.18), concentrations were si gnificantly lower in the morphine group than the placebo group. Furthermore, nor adrenaline concentrations were related to the length of stay in the neonatal int ensive care unit. Conclusions: Continuous morphine injection significantly decrea sed plasma noradrenaline concentrations in ventilated newborns compared with pla cebo treatment. The results of this study support the idea that routine that morphine administration reduces stress responses in ventilated neonates.