Search for fourth generation quarks and leptons at the Fermilab Tevatron and CERN Large Hadron Collider

If next generations of heavy quarks, leptons and neutrinos exist within the Standard Model, they could manifest themselves in Higgs boson production at the Tevatron and the LHC, before being actually observed. One such additional generation would lead to an increase of the Higgs boson production cross section via gluon fusion at hadron colliders of a factor $6\div 9$. So, the study of this process at the Tevatron and LHC can finally fix the number of generations in the SM.