  The equivalence theorem is an extremely useful tool to calculate heavy Higgs
{\it and} top-quark effects for processes that have center-of-mass-energies
(much) larger than the $W$ boson mass. After an explanation of the
renormalization procedures involved, the results for one- and two-loop
radiative corrections to the fermionic Higgs decay, $H\rightarrow f\bar f$, are
given and discussed. Finally, the renormalization scheme dependence is
examined, and the reliability of the perturbative series is investigated.
