Stone works in the hypogea were studied to individualize the microorganisms responsible for the biodeterioration. To ascertain the presence of biodeteriogens (chemiolithotrophic bacteria, algae and heterotrophic microorganisms), culture analyses were carried out; at the same time the presence of microorganisms not necessarily biodeteriogens investigated in order to identify possible relationships among microbial populations. Test results indicate that the most numerous micro-organisms in this monument are actinomycetes and heterotrophic bacteria. They set in following primary colonization of chemio-lithotrophic microorganisms.