Supersymmetric extensions of the standard model generically contain stable
non-topological solitons, Q-balls, which carry baryon or lepton number. We show
that large Q-balls can be copiously produced in the early universe, can survive
until the present time, and can contribute to dark matter.Comment: 16 pages, 3 figures (epsf); replaced with a final version, to appear
in Phys. Lett. B (references added
