  We study the finite-temperature effective potential of the Minimal
Supersymmetric Standard Model, in the limit of only one light Higgs boson.
Because of the large top Yukawa coupling, there can be significant differences
with respect to the Standard Model case: for given values of the Higgs and top
masses, little supersymmetry breaking in the stop sector can make the phase
transition more strongly first-order. After including the full structure of the
stop mass matrix, the most important experimental constraints and the leading
plasma effects, we find that the present limits on Higgs and squark masses are
still compatible with the scenario of electroweak baryogenesis, in a small
region of parameter space corresponding to $m_h \simlt 70 \gev$ and $\msba
\simlt 105 \gev$.
