  We present the first experimental limits on high-q^2 contributions to
charmless semileptonic B decays of the form expected from the Weak Annihilation
(WA) decay mechanism. Such contributions could bias determinations of |Vub|
from inclusive measurements of B-> X_u lnu. Using a wide range of models based
on available theoretical input we set a limit of (Gamma_WA/Gamma_b->u) < 7.4%
(90% confidence level) on the WA fraction, and assess the impact on previous
inclusive determinations of |Vub|.
