This study was designed to evaluate the sympathoadrenal system in rat IUGR fetuses prepared by the Wigglesworth method. Samples were obtained on day 20 of gestation. In the amniotic fluid, concentrations of norepinephrine (NE) and particularly epinephrine (E) were significantly higher in IUGR fetuses than in normally developed fetuses (NE: p less than 0.05, E: p less than 0.01). L-Dopa and three catecholamines in the adrenal glands were decreased in IUGR fetuses. The mol ratios (L-dopa: dopamine: NE: E) were 1: 4: 35: 63 in IUGR fetuses and 1: 5: 39: 87 in normal fetuses. The ratio for epinephrine to L-dopa was significantly lower in IUGR fetuses (p less than 0.05). Adrenal phenylethanolamine-N-methyltransferase activities showed no difference between the two groups. From these results, adrenal epinephrine synthesis in IUGR fetuses was thought to be normal. Because of the depletion of adrenal epinephrine in IUGR fetuses, the plasma epinephrine concentrations were significantly lower after acute hemorrhagic shock (p less than 0.01). However, the plasma concentrations of dopamine and norepinephrine were significantly higher (dopamine: p less than 0.01, NE: p less than 0.001) in IUGR fetuses. These findings suggest that the hypersecretion of adrenal epinephrine is a protective response to chronic stress and the decrease of adrenal epinephrine may be a causative factor for the reduced reserves in the defense mechanism of IUGR fetuses.