  We discuss local duality for weak non leptonic B and Lambda_b decays in the
m_b -> infinity limit under the hypothesis of factorization and in the
Shifman-Voloshin limit. We show that, under these hypotheses, local duality
holds for the first two terms in the 1/m_b expansion and at the order alpha_s
in the perturbative expansion. The possible relevance of these results for the
operator product expansion evaluation of the b-hadron lifetimes is discussed.
