  We present complete one-loop radiative corrections to the decay rate of a top
quark into a charged Higgs boson and a bottom quark, and for the decay of a
charged Higgs boson into leptons. The results are discussed in the framework of
the two Higgs boson extension of the Standard Model suggested by supersymmetry.
The effect of electroweak corrections after exclusion of universal corrections
$\Delta r$ is found to decrease the partial width of the top quark typically by
5%.
