Mould growth in buildings is a major health issue, but most investigations, of the indoor air spora still employ culture-based methods. These are inadequate for assessing exposure, since culturable organisms comprise a small fraction of the total of potentially allergenic/toxigenic units in air. For epidemiological studies, measurement of airborne fungal biomass over extended periods may be more relevant than total counts. Whilst (1 ? 3)-ß-D-glucan has been used to assess airborne biomass, ergosterol may be the best indicator of exposure. For case studies, patients' serum has been used to detect specific spores on sampler slides, and both highly specific and less specific antisera could be used either via fluorescent antibody technique or enzyme-linked immunosorbent assays. In the future, solid-phase polymerase chain reaction (PCR) may be used to detect pathogens or other well-characterized potentially harmful species, and in at least some groups mycotoxin/secondary metabolite/volatile profiles may be used in identification.