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 %$M_{ Z'}^{ lim}$.
Categories: hep-ph