  We present results of a lattice study of the form factors in the decay B-> pi
l nu. We attempt to disentangle the the dependence of the form factors on the
light quark masses and the momentum transfer. Using models of the q^2
dependence we calculate the total decay rate, and compare to the experimental
measure to extract Vub. This study was performed in the quenched approximation
at beta=6.2 on a 24^3 X 48 lattice, with a non-perturbatively improved SW
fermion action.
