Lichens growth is frequently widespread on surfaces of monumental stones and archeological areas. These symbiotic organisms may be harmful to stone substrata due both to their metabolic activity and to the induced physical-mechanical stresses exerted by the thalli. The topic related to their elimination is under debate, and usually their removal is carried out applying biocide formulates or physical stresses. The effective biocidal action of such treatments can be evaluated by some methods such as chlorophyll fluorescence measurements or live/dead staining. Since a damaged organism changes its cell functionality, a simple method based on the measurements of these changes, at a physiological level, can be applied. The induced damage on the cell-membranes can be evaluated by measuring the amount of leached ions by the whole symbiotic organism (both photobiont and mycobiont components) using the electrical conductivity (EC) method. In this study different stress actions (e.g. temperature heating and chemical treatment using the biocide Rocima 103), were applied on lichens growing on monumental stone surfaces. The vitality of treated and untreated samples was evaluated by ions leakage and chlorophyll fluorescence measurements. The EC is a sensitive method for measuring the induced stress either on crustose lichens with a thick thallus or on foliose ones. This technique can be successfully used in the Cultural Heritage field, especially when the most suitable treatment conditions for implementing new control methods must be evaluated. In this paper, possible EC interferences of the lichens with stone substrata and with the applied biocide are discussed and solutions are suggested.