  We calculate the baryon asymmetry generated at the electroweak phase
transition in the minimal supersymmetric standard model, treating the particles
in a WKB approximation in the bubble wall background. A set of diffusion
equations for the particle species relevant to baryon generation, including
source terms arising from the CP violation associated with the complex phase
$\delta$ of the $\mu$ parameter, are derived from Boltzmann equations, and
solved. The conclusion is that $\delta$ must be $\gsim 0.1$ to generate a
baryon asymmetry consistent with nucleosynthesis. We compare our results to
several other recent computations of the effect, arguing that some are
overestimates.
