  We consider the gluon fusion production cross section of a scalar Higgs boson
in models where fermion and scalar massive colored particles are present. We
report analytic expressions for the matrix elements of $gg\to Hg$, $q\bar{q}\to
Hg$, and $qg\to Hq$ processes completing the calculation of the NLO QCD
corrections in these extended scenarios. The formulas are written in a complete
general case, allowing a flexible use for different theoretical models.
Applications of our results to two different models are presented: i) a model
in which the SM Higgs sector is augmented by a weak doublet scalar in the
$SU(N_c)$ adjoint representation. ii) The MSSM, in the limit of neglecting the
gluino contribution to the cross section.
