This study was conducted to determine whether conidia of Stachybotrys-atra contained macrocyclic trichothecenes. The conditions of aerosol generation were such as to reduce the number of larger particles from that which would be expected to occur in the workplace, so as to more easily fulfill the purpose of the study by enriching the small particle component. A total of 7,163 particles in 100 microscopic fields were classified as conidia, hyphal fragments, and other. Conidia and respirable size hyphal fragments made up greater than 90 percent of the total respirable airborne fragments. A dose dependent inhibition of protein synthesis in rat alveolar macrophages was noted within 1 hour following contact with extracts from spore preparations. The ability of mouse thymocytes to respond to crude preparations of rat interleukin-1 was greatly inhibited by satratoxin-H (53126640) and the spore extracts. Analysis indicated that each filter contained one or more of the specific trichothecenes. Stachybotrys species have been much less frequently noted in surveys of airborne fungi in homes and offices than other genera, and thus they may have seemed to be of lesser importance. However, the trichothecene mycotoxins are acutely toxic to a variety of mammalian species, strongly inhibit protein, DNA, and RNA synthesis in eucaryotic cells, and are immunotoxic in rats and mice. The finding of trichothecene mycotoxins in aerosolized respirable conidia of S-atra demonstrates the possibility for pulmonary exposure of workers to these toxins contained in moldy hay, contaminated ductwork, and carpets heavily contaminated by S-atra.