Abstract: A method for monitoring a hidden coal-rock interface, comprising the steps of irradiating the medium (M) being monitored from a gamma-ray source (1) and registering by a detector (2) the intensity of backward scattered radiation at a distance (A) from the surface of the medium (M) and at a distance (B) from the radiation source (B). Two zones (Z.sub.1 and Z.sub.2) are formed at the detector (2) for reception of backward scattered radiation, differently spaced from the source (1), so that the intensity of backward scattered radiation received by the zone (Z.sub.1) closer to the source (1) diminished with the distance (A) from the detector (2) to the medium (M), and grows when received by the zone (Z.sub.2) far from the source (1). The intensities of backward scattered radiation of both zones (Z.sub.1 and Z.sub.2) are summed up to obtain total intensity invariant with respect to variations of the distance (A) between the detector (2) and the medium (M).