  It has been argued recently that the so-called nuclear modification factor
($R_{AA}$) is an observable useful for identifying the quark-gluon plasma. We
discuss the effect of Fermi motion in nuclei on $R_{AA}$ at CERN SPS and BNL
RHIC energies. Contrary to the simple intuition, rather large effects are found
for CERN SPS. The Fermi motion in nuclei contributes significantly to the
Cronin effect. The effect found is qualitatively similar to the one observed
experimentally at CERN energies and similar to the one obtained in the models
of multiple scattering of initial partons. We predict different size of the
effect for different types of hadrons, especially at low energies.
