  The virtual corrections to the production cross section of a Standard Model
Higgs boson are computed up to order \alpha_s^4. Using an effective Lagrangian
for the limit M_t -> \infty, we evaluate the relevant massless two-loop vertex
diagrams by mapping them onto three-loop two-point functions, following a
method recently introduced by Baikov and Smirnov. As a result, we find a
gauge-invariant contribution to the total Higgs production cross section at
NNLO.
