  We study the nonequilibrium characteristics of superconducting tunnel
structures in the case when one of the superconductors is a small island
confined between large superconductors. The state of this island can be probed
for example via the supercurrent flowing through it. We study both the
far-from-equilibrium limit when the rate of injection for the electrons into
the island exceeds the energy relaxation inside it, and the quasiequilibrium
limit when the electrons equilibrate between themselves. We also address the
crossover between these limits employing the collision integral derived for the
superconducting case. The clearest signatures of the nonequilibrium limit are
the anomalous heating effects seen as a supercurrent suppression at low
voltages, and the hysteresis at voltages close to the gap edge $2\Delta/e$,
resulting from the peculiar form of the nonequilibrium distribution function.
