Multijet events at large transverse energy (Sigma E-T>420 GeV) and lar
ge multijet invariant mass (m(jets) > 600 GeV) have been studied by th
e CDF Collaboration at the Fermilab Tevatron. The observed jet multipl
icity distribution can be understood in a QCD-inspired exponentiation
model, in regions of phase space which require going beyond fixed orde
r perturbation theory.