  We study the scaled variances of multiplicity fluctuations in nucleus-nucleus
collisions at SPS and RHIC energies within the HSD transport model. The HSD
results are compared with proton-proton data and with predictions of the
hadron-resonance gas statistical model. We find that the HSD scaled variances
$\omega_i$ for negatively, positively, and all charged hadrons in central
nucleus-nucleus collisions remain close to the $\omega_i$ values in
proton-proton collisions and increase with collision energy as the
corresponding multiplicities per participating nucleon. The statistical model
predicts very different behavior of $\omega_i$. However, a comparison with
preliminary NA49 data for the most central Pb+Pb collisions at SPS energies
does not permit to distinguish the HSD and statistical model results. New
measurements of the multiplicity fluctuations in nucleus-nucleus collisions in
a wide energy region with large acceptance are needed to allow for a proper
determination of the underlying dynamics.
