The invention relates to a so-called bone cement, e.g. based on polymethylmethacrylate, polystyrene or copolymers, whose particles comprised of e.g. polymerizate, additives and/or contrast media have a globular, preferably spheroidal, shape and form the powdery constituents. The invention also relates to an advantageous contrast medium itself, whereby these particles comprise, in essence, relatively large uniform dimensions and preferably form a hexagonally close sphere packing when mixed with the monomer. The invention also relates to a bone cement comprising an accelerator which has an improved physiological acceptability and comprising a catalyst that is specially deposited on the particles. The corresponding bone cement mixtures can be mixed without difficulties and without the risk of entrapping air. The required quantity of monomers is reduced, the heat emission and the volume shrinkage during polymerization are lower, the bending tensile strength of the cured product is at least identical or greater, and the abrasive effect is reduced. In addition, a reduced residual quantity of monomers is expected.