  We discuss the constraints on the AGN evolution from the cosmic X-ray
background and source counts. A synthesis model to fit the X-ray background is
presented. In the model, the spectrum of type 2 AGN has been modeled including
Compton down--scattering within the absorbing material. Besides, we introduced
a dependence on redshift of the relative number of obscured sources and found a
decrease of the fraction of type 2 AGN at redshifts larger than 2.
