Abstract: Composite materials for prosthesis purposes are indicated, which consist of a plastics matrix and an inorganic radiopaque filler which, as the essential components, contains a combination of compounds of the elements Gd, Sr and, if appropriate, La. The proportion of filler in the total composite material is between 20 and 90% by weight.The filler particles are in a silanized form of glass and/or glass ceramics and/or a sintered product and/or in the form of a mixture of their starting components and comprise (in % by weight): 1-31 of Gd.sub.2 O.sub.3, 7-32 of SrO, 0-18 of La.sub.2 O.sub.3, 14-62 of SiO.sub.2, 0-30 of B.sub.2 O.sub.3, 1-33 of Al.sub.2 O.sub.3 and 0-16 of Na.sub.2. A partial replacement of one or more of the radiopacity-causing compounds (Gd.sub.2 O.sub.3 SrO, La.sub.2 O.sub.3) by oxides of the elements Ca, Mg, Y, Zr, Ti, Ta and/or Nb is possible.