  Within the blazar population, hard X-ray selected objects are of particular
interest as they tend to lie at each end of the blazar sequence. In particular,
flat spectrum radio quasars located at high redshifts display the most powerful
jets, the largest black hole masses and the most luminous accretion disks:
their spectral energy distribution has a Compton peak in the sub-MeV region
which favours their detection by instruments like INTEGRAL/IBIS and Swift/BAT.
These sources are even more extreme than blazars selected in other wavebands,
like, for example, the gamma-ray range explored by Fermi. Here we report on a
sample of 12 high redshift blazars detected so far by INTEGRAL, including 3
newly identified objects. Some properties of the combined IBIS/BAT sample of
high redshift blazars (z>2) are also compared to those of a similar similar
sample obtained by Fermi.
