  Model independent search for signals of heavy Z' gauge bosons in low-energy
four-fermion processes is analyzed. It is shown that the renormalizability of
the underlying theory containing Z', formulated as a scattering in the field of
heavy virtual states, can be implemented in specific relations between
different processes. Considering the two-Higgs-doublet model as the low-energy
basis theory, the two types of Z' interactions with light particles are found
to be compatible with the renormalizability. They are called the Abelian and
the "chiral" couplings. Observables giving possibility to uniquely detect Z' in
both cases are introduced.
