The role of indoor plantings as allergen sources was assessed by direct sampling of interior air. Homes with 10 or more plants in one room and three University of Michigan greenhouses were studied by means of a dc-powered rotorod and separate Andersen viable sampler collections incubated at 23 degrees and 50 degrees C. Sequential 30 and 60 sec Andersen samples were obtained during 15 min rotorod collections before and during watering of plants as well as during disturbance of foliage by a small fan. Relative humidity averaged 51% in homes and 78% in greenhouses. Aspergillus fumigatus recoveries were rare. Thermophiles, primarily bacteria, were present at low-to-moderate levels in homes, did not increase with watering of fan in homes, and rose only slightly with disturbance at greenhouse sites. Cladosporium and Penicillium dominated Andersen collections. Watering and fan increased levels of these taxa as well as rotorod recoveries of Alternaria. Epicoccum, and Pithomyces slightly in homes and markedly at greenhouse sites. We conclude that modest numbers of undisturbed house plants contribute minimally to aeroallergen prevalence in homes. However, especially under greenhouse conditions, plantings can harbor abundant fungus growth that may become airborne, especially when agitated directly.