  Constraints on extra neutral gauge bosons are obtained from
$e^+e^-\rightarrow f\bar f$ at NLC energies. Model independent limits on the
$Z'f\bar f$ couplings and lower limits on the $Z'$ mass are discussed. Typical
GUTs with $M_{Z'}$ up to (3 -- 6) $\sqrt{s}$ can be excluded. A distinction
between different GUT scenarios is possible if $M_{Z'}\le 3\sqrt{s}$. Radiative
corrections give only small changes to the $Z'$ exclusion limits provided that
appropriate cuts are applied. %The inclusion of systematic errors leads to
slightly worse results for %$M_{Z'}^{lim}$.
