The Chiostro delle Rane is a part of a single transformation project planned by Bramante in the church complex of S. Maria delle Grazie in Milan. During a restoration at the end of the 19th century, the consolidation of the colonnade involved replacement of deteriorated columns, while the bulging ones were brought back in position. The recent restoration of the cloister completed in 1984 is described in detail. Investigations, analyses and testing of materials are fully reported, as well as tests on products for stone consolidation and protection. Packs of attapulgite with added B57 were applied for cleaning, while silicone resin 11309 was used for consolidation. Surface protection was achieved by methylsilicone resin silirain 50. The same products were used in the treatment of decayed brickwork. Photographs, references.