  If next generations of heavy quarks and leptons exist within the standard
model (SM), they can manifest themselves in Higgs boson production at the
Tevatron and the LHC, before being actually observed. This generation leads to
an increase of the Higgs boson production cross section via gluon fusion at
hadron colliders by a factor 6-9. So, the study of this process at the Tevatron
and LHC can finally fix the number of generations in the SM. Using the $WW^*$
Higgs boson decay channel, the studies at the upgraded Tevatron will answer the
question about the next generation for mass values 135 GeV $\lsim M_H\lsim 190$
GeV. Studying the $\tau\bar{\tau}$ channel we show its large potential for the
study of the Higgs boson at the LHC even in the standard case of three
generations. At the Tevatron, studies in this channel could explore the mass
range 110-140 GeV.
