A large number of studies suggests that the oviduct exerts an importan
t role in early embryonic development but its nature is far from being
elucidated. At present embryotrophic action seems to be based upon th
e interaction between the embryo and various groups of molecules. Thes
e include (a) specific proteins secreted by the epithelium of restrict
ed oviduct regions; (b) growth factors normally present also in other
districts of the organism, whose ligand and receptors genes are often
expressed both in the oviduct and in the embryo, (c) various metabolit
es, such as glucose, oxygen and free radicals scavengers, which determ
ine the environment where the developmental potential of fertilized eg
gs can be fully expressed. These groups of substances will be examined
in some details giving particular emphasis to most recent acquisition
s.