Current techniques are unable to detect either moulds at an early stage in their development or hidden contaminants. Thus most cases of fungal development are only detected once major damage to colonised substrates has been observed. In this context, the aim of the present study was to develop a methodology based on measuring the Volatile Organic Compounds (VOC) emitted by these micro-organisms and adapted to monitoring works of art in terms of the risks of mould development. This article describes the development of four specific indices. One of these indices was tested in situ during measurements performed in the prehistoric Lascaux caves contaminated by Fusarium solani, before and after the site was treated with biocidal agents. Preliminary tests were also carried out using polymer sensors which, in the laboratory, were able to discriminate between mould-affected and sterile environments.