  It is proved by a functional method that the conventional expression for the
Dirac current is the only conserved 4-vector implied by the Dirac equation that
is a function of just the quantum state. The demonstration is extended to
derive the unique conserved currents implied by the coupled Maxwell-Dirac
equations and the Klein-Gordon equation. The uniqueness of the usual Pauli and
Schrodinger currents follows by regarding these as the non-relativistic limits
of the Dirac and Klein-Gordon currents, respectively. The existence and
properties of further conserved vectors that are not functions of just the
state is examined.
