  We compute the two-loop electroweak corrections due to the top quark to the
gluon fusion production cross section of an intermediate-mass Higgs boson. This
result, together with the previously known contribution due to the light
fermions, allows a complete determination of the two-loop electroweak
corrections to this production cross section. For Higgs mass values above 120
GeV the top corrections have opposite sign of the light fermions contribution,
however they are always smaller in size reaching at most 15% of the latter. The
total electroweak corrections to the gluon fusion production cross section for
115 GeV < m_H < 2 m_W range from 5% to 8% of the lowest order term.
