  High redshift blazars are among the most powerful objects in the Universe.
Although they represent a significant fraction of the extragalactic hard X-ray
sky, they are not commonly detected in gamma-rays. High redshift (z>2) objects
represent <10 per cent of the AGN population observed by Fermi so far, and
gamma-ray flaring activity from these sources is even more uncommon. The
characterization of the radio-to-gamma-ray properties of high redshift blazars
represent a powerful tool for the study of both the energetics of such extreme
objects and the Extragalactic Background Light. We present results of a
multi-band campaign on TXS 0536+145, which is the highest redshift flaring
gamma-ray blazar detected so far. At the peak of the flare the source reached
an apparent isotropic gamma-ray luminosity of 6.6x10^49 erg/s, which is
comparable with the luminosity observed from the most powerful blazars. The
physical properties derived from the multi-wavelength observations are then
compared with those shown by the high redshift population. In addition
preliminary results from the high redshift flaring blazar PKS 2149-306 will be
discussed.
