  There are several possibilities to constrain the value of the magnetic field
in the ICM, the most direct ones being the combination of inverse Compton and
synchrotron observations, and the Faraday rotation measures. Here we discuss on
the possibility to provide constraints on the magnetic field in the ICM from
the analysis of the statistical properties of the giant radio halos, Mpc--scale
diffuse radio emission in galaxy clusters. Present observations of a few well
studied radio halos can be interpreted under the hypothesis that the emitting
relativistic electrons are re-accelerated on their way out. By using
statistical calculations carried out in the framework of the re-acceleration
model we show that the observed radio--power vs cluster mass correlation in
radio halos can be reproduced only by assuming $\mu$G fields in the ICM and a
scaling of the magnetic field with cluster mass $B \propto M_v^b$, with $b \geq
0.6$. We also show that the expected occurrence of radio halos with mass and
redshift, and their number counts are sensitive to the magnetic field intensity
in massive galaxy clusters and to the scaling of B with cluster mass. Thus
future deep surveys of radio halos would provide constraints on B in galaxy
clusters.
