This paper reviews some basic principles underlying the measurement of fungi in air samples and dust to describe their quantitative and qualitative value. We compare the results of such measurements with our experience in the Wallaceburg study wherein ca. 400 homes in southern Ontario were studied for various exposure and health outcomes. Until more powerful methods to determine quantitative and qualitative exposures to fungi are developed, the attributable risk of fungal contamination in residential housing for public health cannot be estimated with accuracy. The most reliable information on mold exposures in residential housing can be obtained by measuring moisture source strength, detailed study of areas of visible mold plus some mycological testing of building materials to determine where the growth is occurring beyond that visible to the naked eye and qualitative and quantitative analysis of molds in settled dust.