The phase diagram of the Ag2Se-Ho2Se3 system in the range of 0-50 mol.% Ho2Se3 was constructed with the results of XRD and differential thermal analysis. A dimorphous compound exists in the system at the equimolar ratio of the components. The investigated part of the Ag2Se-AgHoSe2 diagram is of the eutectic type with the eutectic coordinates 7 mol.% Ho2Se3 and 1125 K. The crystal structure of the high-temperature modification of AgHoSe2 was studied by X-ray powder diffraction method. alpha-AgHoSe2 is described as a NaCl structure (space group Fm (3) over barm) with the lattice parameter a = 5.7623(3) angstrom. Atomic parameters were calculated in the isotropic approximation (R-I = 0.0434 and R-P = 0.0636). The crystal structure of beta-AgHoSe2 was determined by X-ray structure analysis and was refined to R = 0.0487. (C) 2006 Elsevier Ltd. All rights reserved.