  We discuss the implications of the proposed gravitational redshift experiment
on antihydrogens. We show that the result should be the same as on hydrogens in
spite of different free-fall accelerations (WEP violation) which may occur if
there is a vector fifth-force field. We emphasize the experiment is unique in
the sense that it tests the Equivalence Principle expressed in its ultimate
form, proposed to be called UEP, directly without being disturbed by the effect
of possible presence of a scalar fifth-force field.
