The crystallization of salts in building stones is one of the most common and severe deteriorating phenomenon developed on Historic Buildings. To evaluate their mechanical effects in treated and non-treated stones, experimental salt crystallization tests and the monitoring of the corresponding acoustic emission/microseismic activity, AE/MS, have been planned. Salt crystallization tests have therefore been performed on a high porosity (30per thousand) limestone used in the building of the Cathedral of Murcia (Spain). Each test consisted of 11 and 20 cycles (for the non-treated and treated specimens, respectively) of immersion of specimens in salt solution (14per thousand Na₂SO₄.10H₂O) for 4 h., drying in an oven at 60°C for 14h. and final cooling at room temperature for 6 h. The treated specimens were consolidated by total immersion in ethyl silicate - Tegovakon V - and protected with a water repellent, oligomeric polysiloxane - Tegosivin HL-100 - (both from Th. Goldschmidt, FRG). The AE/MS, was monitored in the 100-300 KHz range. The preliminary results show a very different AE/MS behaviour between the non-treated and the treated specimens.