We studied factors that predict in children catecholamine induced vasoconstriction of the persistent arterial duct. Epinephrine at 2.0–10.0 (4.9 ± 1.3, mean ± standard deviation) μg/kg was injected intravenously into 30 patients with persistent arterial duct whose age ranged from 1 to 91 (27 ± 26) months. In 11 patients aged 10–66 (34 ± 23) months (responders), a continuous murmur had almost completely disappeared on auscultation, and both the diameter and the shunt flow area of the arterial duct had become smaller as shown by Doppler echocardiography. On the other hand, there was no such change in 19 patients aged 1–91 (23 ± 27) months (non-responders). Although there was no significant difference in the age, the body weight, the minimal diameter of the arterial duct, or the doses of epinephrine between responders and non-responders, the gestational age at birth was slightly less (p=0.09) and the birth weight was significantly smaller in responders than in non-responders (p<0.05). The persistent arterial duct of those who had a history of low birth weight always responded to epinephrine. In infants younger than 6 months, the persistent arterial duct was never constricted by epinephrine regardless of the birth weight and gestational age. In low birth weight infants, the vascular smooth muscle of the persistent arterial duct can usually constrict beyond infancy. There may be some age dependent difference in responsiveness to epinephrine until 6 months of age.