  We study the polarization change of Lambda^0's produced in ultra-relativistic
heavy-ion collisions with respect to the polarization observed in proton-proton
collisions as a signal for the formation of a Quark-Gluon Plasma (QGP).
Assuming that, when the density of participants in the collision is larger than
the critical density for QGP formation, the Lambda^0 production mechanism
changes from recombination type processes to the coalescence of free valence
quarks, we find that the Lambda^0 polarization depends on the relative
contribution of each process to the total number of Lambda^0's produced in the
collision. To describe the polarization of Lambda^0's in nuclear collisions for
densities below the critical density for the QGP formation, we use the
DeGrand-Miettinen model corrected for the effects introduced by multiple
scattering of the produced Lambda^0 within the nuclear environment.
