Events in (p) over bar p collisions at root s = 1.8 TeV with total transver
se energy exceeding 500 GeV are used to set limits on quark substructure. T
he data are consistent with next-to-leading order QCD calculations. We set
a lower limit of 2.0 TeV at 95% confidence on the energy scale Lambda(LL) f
or compositeness in quarks. assuming a model with a left-left isoscalar con
tact interaction term. The limits on Lambda(LL) are found to be insensitive
to the sign of the interference term in the Lagrangian.