  Signals of QCD instanton-induced processes are searched for in deep-inelastic
scattering (DIS) at the electron-proton collider HERA in a kinematic region
defined by the Bjorken-scaling variables x > 10^(-3), 0.1 < y < 0.6 and photon
virtualities 10 <= Q^2 < 100GeV^2. Several observables characterising hadronic
final state properties of QCD instanton-induced events are exploited to
identify a potentially instanton-enriched domain. While an excess of events
with instanton-like topology over the expectation of the standard DIS
background is observed it can not be claimed to be significant given the
uncertainty of the simulation. Upper limits on the cross-section for
instanton-induced processes of between 60pb and 1000pb are set dependent on the
kinematic domain considered. The data do not exclude the cross-section
predicted by instanton perturbation theory for small instanton sizes. At large
instanton sizes a naive extrapolation of instanton perturbation theory yields a
cross-section in the range of sensitivity of this study. Such a cross-section
is not observed, in agreement with non-perturbative lattice simulations of the
QCD vacuum.
