Describes a research project undertaken within the framework of the strategic Cultural Heritage project initiated by the Italian National Research Council. It assessed the vitality of the fungal spores that accumulate on certain types of material (paper, wood, metal, glass), depending upon differing microclimates and the effects of time. Among the fungal species that damage books the authors decided to select the genera Aspergillus, Penicillium and Stachybotrys, from the class of Deuteromycetes, and the genus Chaetomium, from the class of Ascomycetes. The purpose of the research is to evaluate the potential risk of infestation from this type of flora, when the hygrometric levels, considered optimal for conservation, are respected. The sampling methods used are qualitative and quantitative. The authors also studied the relationship between the water activity contained in the various types of paper and the spore's ability to germinate.