  A synthesis model for the cosmic X-ray Background (XRB) is presented, which
includes a proper treatment of Compton scattering in the absorbing matter for
type 2 AGN. Evidence for a decrease of the relative importance of type 2 AGN at
high redshift is found, which may be due either to a decrease of the relative
number of obscured sources, or (more plausibly) to an increase of the fraction
of Compton-thick absorbed sources. The XRB spectrum, soft X-rays and hard
X-rays source counts can be simultaneously fitted only if the XRB normalization
as derived from BeppoSAX/MECS measurements is adopted.
