  We compute the three-dimensional effective action for the minimal
supersymmetric standard model, which describes the light modes of the theory
near the finite-temperature electroweak phase transition, keeping the one-loop
corrections from the third generation quarks and squarks. Using the lattice
results of Kajantie {\it et al.}\ for the phase transition in the same class of
3-D models, we find that the strength of the phase transition is sufficient for
electroweak baryogenesis, in much broader regions of parameter space than have
been indicated by purely perturbative analyses. In particular we find that,
while small values of $\tan\beta$ are favored, positive results persist even
for arbitrarily large values of $\tan\beta$ if the mass of the $A^0$ boson is
between 40 and 120 GeV, a region of parameters which has not been previously
identified as being favorable for electroweak baryogenesis.
