  The nature of the ultraluminous X-ray sources (ULX) is still to be
understood. Several hypotheses have been suggested to explain the high X-ray
luminosity: stellar mass black holes with emission collimated by relativistic
effects or anisotropies in the accretion disk, intermediate mass black holes,
young supernovae remnants, background active galactic nuclei. To discriminate
among the above hypotheses, the search for relativistic effects can be a
valuable "pathfinder". Here we propose a list of ULX candidates suitable to
show relativistic beaming
