Internal Dynamics of Distant Clusters

We consider a sample of about 50 distant clusters at z> 0.15 (<z>=0.3), each cluster having at least 10 galaxies and evaluate in a homogeneus way cluster velocity dispersions and optical virial masses. We apply the same procedures already successfully applied on a sample of nearby clusters in order to properly analyze the possible dynamical evolution of galaxy clusters. We do not find any evidence for an evolution of cluster properties.