  We use a multiply-subtracted Omnes dispersion relation for the form factor
f^+ in B->pi semileptonic decay, allowing the direct input of experimental and
theoretical information to constrain its dependence on q^2. Apart from these
inputs we use only unitarity and analyticity properties. We obtain
|V(ub)|=(4.02 \pm 0.35)\times 10^{-3}, improving the agreement with the value
determined from inclusive methods, and competitive in precision with them.
