  We present explicit analytic results for the two-loop top/stop/gluino
contributions to the cross section for the production of CP-even Higgs bosons
via gluon fusion in the MSSM, under the approximation of neglecting the Higgs
boson mass with respect to the masses of the particles circulating in the
loops. The results are obtained employing the low-energy theorem for Higgs
interactions adapted to the case of particle mixing. We discuss the validity of
the approximation used by computing the first-order correction in an expansion
in powers of the Higgs boson mass. We find that, for the lightest CP-even Higgs
boson, the gluino contribution is very well approximated by the result obtained
in the limit of vanishing Higgs mass. As a byproduct of our calculation, we
provide results for the two-loop QCD contributions to the photonic Higgs decay.
