  We show that the Riemannian Schwarzschild and the ``Taub-bolt'' instanton
solutions are the only spaces (M,g) such that
  1) M is a 4-dimensional, simply connected manifold with a Riemannian,
Ricci-flat C^2-metric g which admits (at least) a 1-parameter group of
isometries H without isolated fixed points on M.
  2) The quotient (M L)/H (where L is the set of fixed points of H) is an
asymptotically flat manifold, and the length of the Killing field corresponding
to H tends to a constant at infinity.
