Impregnation of very small pores and cracks in large specimens calls for impregnating materials of the maximum fluidity. Recent trials showed that monomeric types of impregnating material give considerably better penetration than the epoxides and polyesters usually used for this purpose. The monomers and their resulting polymers have certain disadvantages compared with the more standard impregnating media. The advantages and problems associated with monomer impregnation are discussed and details are given of a simple impregnation technique employing the monomer styrene. -- AATA