  We have studied the restoration of chiral symmetry in lattice QCD at the
finite temperature transition from hadronic matter to a quark-gluon plasma. By
measuring the screening masses of flavour singlet and non-singlet meson
excitations, we have seen evidence that, although flavour chiral symmetry is
restored at this transition, flavour singlet (U(1)) axial symmetry is not. We
conclude that this indicates that instantons continue to play an important role
in the quark-gluon plasma phase.
