Non-destructive testing in microbiology applied to the conservation of works of art involves sampling operations that do not damage the integrity of the work, and is performed by simple and elementary techniques aimed at collecting samples representative of a state of normal biological pollution or of a specific pathology produced by microbiological attacks. No analytical data are obtained from the sample as such, but only after thr preparation of a successive series of tests, either on site or later in the laboratory. The sampling should be done in view of subsequent analyses, and to be valid it should permit at least two analyses: the plating into nutrient media and microscopic examinations, obtaining ideally, the same results from both the analyses. The aim of this work is to illustrate, the the first part, non-destructive tests already recorded or being experimented with, referred to different works of art as well as to the dynamics of the same sampling; and in the second part the results of research on problems on non-destructive samples referred to canvas paintings as well as to photographic materials, with comparison and discussion of the advantages, limitations or disadvantages of each of the techniques applied or experimented with.