Duality and quantum-algebra symmetry of the A_(N-1)^(1) open spin chain with diagonal boundary fields

We show that the transfer matrix of the A_{N-1}^(1) open spin chain with diagonal boundary fields has the symmetry U_q (SU(L)) x U_q (SU(N-L)) x U(1), as well as a ``duality'' symmetry which interchanges L and N - L. We exploit these symmetries to compute exact boundary S matrices in the regime with q real.