The day 13–14 chicken embryo is a useful model for studies on prenatal stress responses. Free dopamine, norepinephrine and epinephrine in its plasma, amniotic and allantoic fluid respond to a variety of stresses. The allantoic fluid also contains conjugated catecholamines and conjugated steroids. However, a blood/allantois barrier excludes free thyroid hormones and free steroids, and insulin. On the other hand, the allantoic fluid contains at least 40 amino acids (including six excitatory amino acids) and related compounds. Most, possibly all, components of the allantoic fluid are regulated at specific blood/allantois and amnion/allantois barriers, and they respond to ethanol stress and metabolite loading differentially. The avian allantois is a depot for important metabolites and messenger substances which seems to be controlled by as yet unidentified hormones