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

If next generations of heavy quarks and leptons exist within the \SM, they can manifest themselves in Higgs boson production at the Tevatron and the LHC, before being actually observed. It leads 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. Using the $WW^*$ and $ZZ^*$ Higgs boson decay channels, the studies at the upgraded Tevatron will answer the question about the next generation for mass values 135 GeV $\lsim M_H\lsim 200$ GeV. Studying the $\tau\bar{\tau}$ channel we show its large potential for the study of the Higgs boson at the LHC. At the Tevatron, studies in this channel could eventually explore the mass range below 135 GeV.