Growth of a mixed microfungal inoculum on natural and synthetic textile substrates was monitored using a quantitative bioluminescent assay of adenosine triphosphate (ATP), based on the firefly luciferin-luciferase reaction. When incubated as specified in the British Standard BS 6085:1981, a positive growth response was observed on each of the six materials tested within hours of initial inoculation. Significant differences in recovered ATP levels were also observed on biocide-treated and untreated wool fabrics. The application of a technique known as ATP imaging, where light emission (generated in situ on textile substrates) is assessed instantaneously, by means of image-intensifier, photomultiplier, or photographic instrumentation, providing a quantitative assessment and spatial distribution recording of microbial growth is discussed.