A new radioenzymatic assay was used to evaluate free and conjugate catecholamines in six pregnant women who underwent cesarean section at term, in their newborns and in the amniotic fluid. Free adrenaline in maternal plasma was higher while noradrenaline and dopamine were lower at the moment of surgery than 24 hours before the operation. In umbilical plasma adrenaline and noradrenaline are higher than in maternal plasma while only traces of free dopamine and salsolinol are present. In the amniotic fluid high levels of free and conjugated salsolinol are found. The high level of free and conjugated catecholamines found in the umbilical plasma demonstrates that fetal sympathetic nervous system is strongly activated at delivery. Furthermore the presence of sulfoconjugating activity similar to that of the adult is confirmed.