It is argued that experiments on rotating superconductors provide evidence for the existence of macroscopic spin currents in
superconductors in the absence of applied external fields. Furthermore it is shown that the model of hole
superconductivity predicts the existence of such currents in all superconductors. In addition it is pointed out that spin currents are required within a related
macroscopic (London-like) electrodynamic description of superconductors
recently proposed. The spin current arises through an
intrinsic spin Hall effect
when negative charge
is expelled from the interior of the metal upon the transition to the superconducting state.