  We report on progress in measuring disconnected correlators associated with
pseudoscalar flavor-singlet mesons. This will eventually allow us to compute
the masses of the eta and eta' mesons. Flavor-singlet physics also presents an
interesting test of the staggered fermion formulation, as disconnected
correlators are sensitive to whether the same action governs both sea quarks
and valence quarks. It can also help test the validity of the ``fourth-root
trick'' used in unquenched lattice calculations where the number of flavors
$N_f<4$.
