  We consider a minimal extension to higher dimensions of the Standard Model,
having one compactified dimension, and we study its experimental tests in terms
of electroweak data. We discuss tests from high-energy data at the $Z$-pole,
and low-energy tests, notably from atomic parity violation data. This
measurement combined with neutrino scattering data strongly restricts the
allowed region of the model parameters. Furthermore this region is incompatible
at 95% CL with the restrictions from high-energy experiments. Of course a
global fit to all data is possible but the $\chi^2_{\rm min}$ for degree of
freedom is unpleasantly large.
