  We consider the isospin breaking corrections to charmless semileptonic decays
of B mesons. Both, the recently measured branching ratios of exclusive decays
by the CLEO Collaboration and the end-point reion of the inclusive lepton
spectrum in form factor models, can be affected by these corrections. Isospin
corrections can affect the determination of |V_ub| from exclusive semileptonic
B decays at a level comparable to present statistical uncertainties.
