  The effects of strong gravity on the polarization of the Compton reflection
from an X-ray illuminated accretion disc are studied. The gravitational field
of a rotating black hole influences Stokes parameters of the radiation along
the propagation to a distant observer. Assuming the lamp-post model, the degree
and the angle of polarization are examined as functions of the observer's
inclination angle, of the height of the primary source and of the inner radius
of the disc emitting region. It is shown that polarimetry can provide essential
information on the properties of black holes sources, and it is argued that
time variation of the polarization angle is a strong signature of general
relativity effects. The expected polarization degree and angle should be
detectable by new generation polarimeters, like the one planned for the Xeus
mission.
