  The parametrized post Newtonian formalism for 5-dimensional metric theories
with a compact extra dimension is developed. The relation of the 5-dimensional
and 4-dimensional formulations is then analyzed, in order to compare the higher
dimensional theories of gravity with experiments. It turns out that the value
of post Newtonian parameter $\gamma$ in the reduced 5-dimensional Kaluza-Klein
theory is two times smaller than that in 4-dimensional general relativity. The
departure is due to the existence of an extra dimension in the Kaluza-Klein
theory. Thus the confrontation between the reduced 4-dimensional formalism and
Solar system experiments raises a severe challenge to the classical
Kaluza-Klein theory.
