  The computational requirements and dynamics of Monte Carlo simulations of
unquenched QCD incorporating the infrared quark eigenmodes (up to $\approx
\Lambda_{QCD}$) exactly and UV modes via a loop representation are discussed.
The accuracy of such a loop representation is studied for a variety of lattice
volumes and quark masses. The method has been successfully applied for lattices
up to 10$^3$x20 at $a \simeq$0.17F with improved (clover) action, and allows
simulations at or near kappa critical.
