The distribution of black staining on the NMAI building was examined during the workshop organized by the MCI in April 2010. The staining was clearly related to preferential water paths where water runs down the surfaces and it is present on the external walls facing any orientation. For these reasons the black staining was attributed to biocolonization, presumably due to cyanobacteria. Other blackened areas not linked to water runoff were observed in some horizontal areas on the south walls. These were somewhat covered with plant debris and the blackening could be ascribed to the presence of other microorganisms, such as fungi, though these have not been examined in detail. Three samples were collected. These were: Sample #2, corresponds to a fragment taken from a first course ashlar (prepared or dressed stonework) of the low wall by the loading dock at the north-west corner of the NMAI building; Sample #5, was a fragment taken from the stained area below the scupper on the east side of the wall on the roof beyond the Inouye Terrace; Sample #7, was a fragment taken from a rather recessed block area of a block in the ashlar course below that of sample #5. The aim of the analyses carried out in the laboratory was to detect microorganisms causing the blackening of the wall surfaces and to investigate their relationships with stone.