  The cosmological relic density of the lightest supersymmetric particle of the
minimal supersymmetric standard model is calculated under the assumption of
gauge and Yukawa coupling unification. We employ radiative electroweak breaking
with universal boundary conditions from gravity-mediated supersymmetry
breaking. Further constraints are imposed by the experimental bounds on the
b-quark mass and the BR(b -> s gamma). We find that coannihilation of the
lightest supersymmetric particle, which turns out to be an almost pure bino,
with the next-to-lightest supersymmetric particle (the lightest stau) is
crucial for reducing its relic density to an acceptable level.

High Energy Physics - Phenomenology