HIGGS POTENTIAL BOUNDS ON EXTRA QUARK-LEPTON GENERATIONS

We consider the bounds for the values of higgs mass M(H) and of the ma ss of the extra quarks and leptons M(extra) derived from the stability of vacuum and from the absence of Landau pole in Higgs potential. We find that in the case of the absence of new physics up to the GUT scal e the bounds for the mass of the 4th generation are so restrictive tha t the negative result of CDF search for extra quarks closes the window for fourth generation. In the case of the absence of new physics up t o 10(5) GeV we get weaker but still nontrivial bounds on M(H) and M(ex tra).