  Disconnected diagrams give crucial contributions to the physics of flavor
singlet hadrons and to scalar form factors of non-singlet hadrons. Naive
lattice calculation of the disconnected diagrams, however, requires a huge
number of fermion matrix inversions and hence a prohibitively large
computational cost. In this article, we present recent studies of the
flavor-singelt meson spectrum and nucleon strange quark content using the
all-to-all propagator to calculate the relevant disconnected diagrams.
