  We present the QCD corrections to Higgs boson self-energies for arbitrary
momentum transfer and for different internal quark masses, to treat the case of
CP--even, CP--odd and charged Higgs bosons which appear in extensions of the
Standard Model scalar sector. Using Ward Identities, we then relate these
results obtained by directly evaluating the relevant two--loop Feynman diagrams
to the known expressions for the electroweak vector boson vacuum polarization
functions. Finally, we derive the exact analytical expressions for the QCD
corrections to the decays of these Higgs particles into quark pairs in the
general case, and reproduce in a completely independent way known results in
some special cases.
