  We present the computation of the leading one-loop electroweak radiative
corrections to the non-standard top quark decay width Gamma(t->H+ b), using a
physically motivated definition of tan(beta). We find that the corrections are
large, both in the Minimal Supersymmetric Standard Model (MSSM) and the
Two-Higgs-Doublet Model (2HDM). These corrections have an important effect on
the interpretation of the Tevatron data, leading to the non-existence of a
model-independent bound in the tan(beta)-MH+ plane.
