  We study the effect of a potential fourth fermion generation on the upper and
lower Higgs boson mass bounds. This investigation is based on the numerical
evaluation of a chirally invariant lattice Higgs-Yukawa model emulating the
same Higgs-fermion coupling structure as in the Higgs sector of the electroweak
Standard Model. In particular, the considered model obeys a Ginsparg-Wilson
version of the underlying $SU(2)_L\times U(1)_Y$ symmetry, being a global
symmetry here due to the neglection of gauge fields in this model. We present
our results on the modification of the upper and lower Higgs boson mass bounds
induced by the presence of a hypothetical very heavy fourth quark doublet.
Finally, we compare these findings to the standard scenario of three fermion
generations.
