  Gravitational waves are generated during first-order phase transitions,
either by turbolence or by bubble collisions. If the transition takes place at
temperatures of the order of the electroweak scale, the frequency of these
gravitational waves is today just within the band of the planned space
interferometer LISA. We present a detailed analysis of the production of
gravitational waves during an electroweak phase transition in different
supersymmetric models where, contrary to the case of the Standard Model, the
transition can be first order. We find that the stochastic background of
gravitational waves generated by bubble nucleation can reach a maximum value
h0^2 Omega_{gw} of order 10^{-10} - 10^{-11}, which is within the reach of the
planned sensitivity of LISA, while turbolence can even produce signals at the
level h0^2 Omega_{gw} \sim 10^{-9}. These values of h0^2 Omega_{gw} are
obtained in the regions of the parameter space which can account for the
generation of the baryon asymmetry at the electroweak scale.
