We study the behavior of the underlying event in large transverse
momentum charged jet and Z-boson production at 1.8 TeV and compare with the
QCD Monte-Carlo models.  The data indicate that neither ISAJET or HERWIG
produce enough charged particles (with p(t) > 0.5 GeV/c) from the
"beam-beam
remnant" component and that ISAJET produces too many charged particles from
initial-state radiation.  PYTHIA which uses multiple parton scattering to
enhance the underlying event does the best job describing the data.