Selected materials, free from biocides, were exposed at the open cleared site at Innisfail, Queensland, in order to observe the process of colonization by microfungi. Specimens were protected from rain and gross debris by a glass canopy. Two series of exposures were conducted, one starting in the wet season, the other in winter. Slow growth initially was attributed to freedom from wetting by rain, but increases in the amounts of fungal growth were observed following weeks in which the RH exceeded 80 percent for more than three-quarters of the time or when the mean RH exceeded 87 percent. Cotton fabric and timber showed the earliest growth and also supported the greatest diversity of genera. After prolonged exposure, the greatest amounts of fungal growth developed on acrylic paint and plasticized poly(vinyl chloride). Cladosporium was the dominant species on all materials; Fusarium and Curvularia were also abundant. See also AATA 13-847 for further information on microbial attack.