  We present our results on multiplicity fluctuations in the framework of the
string clustering approach. We compare our results --with and without
clustering formation-- with CERN SPS NA49 data. We find a non-monotonic
behaviour of these fluctuations as a function of the collision centrality,
which has the same origin as the observed fluctuations of transverse momentum:
the correlations between the produced particles due to the cluster formation.
