We compared the extrauterine adaptation of preterm with term newborn infants, by sequentially measuring plasma catecholamine (CAT) levels at birth and during the first 24 h of life. Twenty-seven preterm appropriate-for-gestational-age (AGA) infants, less than 35 weeks gestation, were compared with 26 healthy near-term AGA infants. Modes of delivery and umbilical arterial pH (mean 7.28) did not differ. Infants with asphyxia, presumed sepsis or hypoglycemia were excluded. CAT (norepinephrine, epinephrine, dopamine) levels were measured by radioenzymatic assay in blood samples from maternal vein, cord vein, cord artery and blood samples obtained at 1, 2 and 24 h of postnatal age. At birth, the cord arterial CAT levels were significantly higher than maternal venous CAT levels in both groups of neonates. Plasma epinephrine levels (mean +/- SD) at 1 and 2 h of postnatal age were significantly higher in preterm than in near-term newborns (0.98 +/- 0.82 nmol/l vs. 0.30 +/- 0.21 nmol/l at 1 h; 0.98 +/- 0.68 nmol/l vs. 0.28 +/- 0.29 nmol/l at 2 h; p < 0.05). The norepinephrine and dopamine measurements did not differ between the two groups studied at birth, 1, 2 and 24 h of postnatal age. These data indicate that the preterm infants (25-35 weeks gestation) are capable of mounting a catecholamine response at birth similar to near-term newborns. The persistent elevation of epinephrine in preterm infants at 1 and 2 h of life may be attributed to either slower clearance of epinephrine or continued stimulation during clinical care in the NICU.