  We study the potential effect of anomalous couplings of the third generation
quarks to gauge bosons in rare B decays. We focus on the constraints from
flavor changing neutral current processes such as $b\to s\gamma$ and $b\to s
\ell^+\ell^-$. We consider both dimension-four and dimension-five operators and
show that the latter can give large deviations from the standard model in the
still unobserved dilepton modes, even after the bounds from $b\to s\gamma$ and
precision electroweak observables are taken into account.
