  Perturbative QCD in the high-energy limit describes the evolution of
scattering amplitudes with increasing energy towards and into the so-called
saturation regime. Comparisons of the predictions with experimental data for a
number of observables led to significant progress and understanding. We discuss
the case of particle-production cross-sections measured at HERA and argue that
these measurements have the potential to provide evidence for the saturation
regime of QCD.
