  We derive a bound on the magnetic dipole moment of the top quark in the
context of the effective Lagrangian approach by using the values of the ratio
$R_b = \Gamma_b/\Gamma_h$, $R_l = \Gamma_h/\Gamma_l$ and $\Gamma_Z$. We found
that the oblique corrections are more sensible than the vertex ones for this
moment.
