  Neutral Higgs-boson pair production provides the possibility of studying the
trilinear Higgs couplings at future high-energy colliders. We present the QCD
corrections to the gluon-initiated processes in the limit of a heavy top quark
in the loops and the Drell-Yan-like pair production of scalar and pseudoscalar
Higgs particles. The pp cross sections are discussed for LHC energies within
the Standard Model and its minimal supersymmetric extension. The QCD
corrections are large, enhancing the total cross sections significantly.
