Research aimed at elucidating the causes of m igrations of thermoplastic resins — employed as solutions for reinforcement of porous stones — has been taken up. Solutions of butyl polymethacrylate have been used for the purpose, the limestone from the region of Pińczów being saturated with them in the tests concerned. The impact exerted by the degree of polymerization of resins, solvents and concentration on capillary ascent o f solutions, the degree of saturation of the stcnes, their drying capacity and finally on the process of migration of resins in the course of drying has been studied. The results of the investigations have made it possible to determine the paramétrés chesking the process o f migration of butyl polymethacrylate to the surface of Pińczów limestone. As has been ascertained, the main cause deciding about the course of migration is viscosity of solutions. Its degree may be adjusted by way of employing polymers with a higher degree of polymerization or by enhancing concentration of the solutions. The first route has been recognized as more efefctive since it provides for multiple repetition of the proceeding by means of diluted solutions what is of great significance from the viewpoint of conservation practice. Now as regards the solvents used, the best results have been obtained in the case of white spirit. Due to the specific phenomena accompanying its evaporation, solutions with a low degree of viscosity may be applied and the effect of structural reinforcement duly achieved. If aromatic hydrocarbons used as solvents, the viscosity of the solutions should amount to 10+15 cP. On the grounds of the results obtained an attempt has been made at elucidation of the phenomena of migration what enables selection of adequate paramétrés providing for structural reinforcement of the monuments built, or made, of porous materials.