On the initiative of the Institute for the Protection of Monuments and with international participation a colloquium on problems of preserving stones took place in Dresden, Karl-Marx-Stadt and Torgau Grosser in May 1971. The discussion included problems connected with the preservation of two architectural monuments: the northern portal of the castlechurch in Karl-Marx-Stadt, and Grosser Wendelstein in the Hartenfels Castle at Torgau. The northern portal consists of porphyric tuff from the surroundings of Karl-Marx-Stadt, whereas quartzitic sandstones from the Saxon and Polish Cretaceous were used for the construction of Grosser Wendelstein. The deterioration of both monuments is so serious that a treatment with stone preservatives was considered. Owing to the insufficient testing of such preservatives at home and abroad, and theproblematic character associated with a complete impregnation of the porphyritic tuffs with solutions of epoxy resin, a treatment of the two monuments by stone preservatives was postponed. A.A. -- AATA