  We report on a study of the pentaquark Theta^+(1540), using a variety of
different interpolating fields. We use Chirally Improved fermions in
combination with Jacobi smeared quark sources to improve the signal and get
reliable results even for small quark masses. The results of our quenched
calculations, which have been done on a 12^3x24 lattice with a lattice spacing
of a=0.148 fm, do not provide any evidence for the existence of a Theta^+ with
positive parity. We do observe, however, a signal compatible with nucleon-kaon
scattering state. For the negative parity the results are inconclusive, due to
the potential mixture with nucleon-kaon and N*-kaon scattering states.
