Prenatal stress in the last trimester of pregnancy induces permanent disorders in sex-specific differentiation of the brain in rats. In order to determine the neuroendocrine response of the fetal hypothalamus to the maternal stress, we investigated the temporal change in fetal hypothalamic catecholamines when their mothers were exposed to an acute stress. On day 20 of gestation, pregnant rats were subjected to forced immobilization and sacrificed at 0, 30, 60, 120 and 180 minutes. Plasma corticosterone reached a peak at 60 minutes of stress in mothers and fetuses. Hypothalamic norepinephrine and epinephrine decreased at 120 and 180 minutes of stress in mothers, whereas in fetuses, hypothalamic norepinephrine decreased at 120 and 180 minutes of stress, and dopamine also showed a tendency to decrease. These results suggest that maternal stress in late pregnancy decreases fetal hypothalamic norepinephrine which is involved in androgen-dependent sex differentiation of the brain.