  We present results from quenched lattice QCD for the form factors for the
decay $B\to\rho l\nu$. The calculations are performed using a nonperturbatively
improved action and operators at two values of the lattice spacing. The bottom
quark mass is reached by extrapolation from simulations performed with heavy
quark masses around the charm mass. Our primary result is for the partially
integrated decay rate $\Gamma_{PI}$ over the range $12.7\gev^2 < q^2 <
18.2\gev^2$:
  \Gamma_PI = (4.9^{+12}_{-10}{+0}_{-14}) X 10^12 s^-1
