Cold polymerizates "Kallocryl K" and "Palacos" were characterized by means of physico-chemical methods of examination. The residual monomer content of the polymerizates, which is of major toxicological interest, was also determined quantitatively. It was possible to show that the residual monomer content decreases exponentially as a function of the duration of polymerization. "Palacos" polymerizates had much higher residual monomer contents than "Kallocryl K" polymerizates when the same time of polymerization was used. Also discussed in this paper are possible methods of reducing the residual monomer content prior to implantation of the plastic materials.