Poly(n-butyl methacrylate) of low viscosity made in the USSR (PBMA) proved to be reversible over 25 years and stable to UVirradiation. New possibilities in the PBMA conservation technique for murals on loess plaster were developed by using mixtures of good and bad solvents for PBMA instead of good solvents only. Thus impregnation by 10% PBMA solution in xylene-ethyl alcohol mixture in comparison with xylene solution of the same concentration gives more regular resin distribution inside porous material and considerably fewer changes in surface optical properties. Acetone-white spirit and some other solvent mixtures are efficient in cleaning and restoring the appearance of murals which were conserved in the field with excess of PBMA. Author's address: The State Hermitage Museum, 191065 Leningrad, USSR.