  First results on a medium-deep X-ray survey in the "new" 5-10 keV band
carried out with the MECS detectors onboard BeppoSAX are presented. The High
Energy Llarge Area Survey (HELLAS) is aimed to directly explore a band where
the energy density of the X-ray background is more than twice than that in the
soft (0.5-2.0 keV) band. The optical identification follow-up of the first ten
HELLAS hard X-ray sources indicate that Active Galactic Nuclei are the dominant
population at 5-10 keV fluxes of the order of 10e-13 cgs. We discuss the
implications of these findings for the AGN synthesis models for the XRB.
