  We have experimentally studied the energy levels of a mesoscopic SQUID using
inelastic Cooper-pair tunneling. The tunneling in a small Josephson junction
depends strongly on its electromagnetic environment. We use this fact to do
energy level spectroscopy of a SQUID-loop by coupling it to a small junction.
Our samples with strong quasiparticle dissipation are well described by a model
of a particle localized in one of the dips in a cosine-potential, while in the
samples with weak dissipation we can see formation of energy bands.
