In this study, we investigated indoor air quality and symptoms of respiratory illness in 264 nursing workers at 28 day-care centers in Taipei. Geometric mean concentrations of indoor and outdoor bacteria were 735 colony-forming units in air (CFU/m3) and 384 CFU/m3, respectively. In addition, geometric mean concentrations of indoor and outdoor fungi were 1,212 CFU/m3 and 1,032 CFU/m3, respectively. Aspergillus, Cladosporium, and Penicillium-microfungi that occurred most commonly-were found indoors and outdoors. Geometric mean concentrations of house dust mite allergens, Der p I and Der p V, were 58 ng/g dust and 14 ng/g dust, respectively. In addition, the observed high prevalence of dampness or mold problems in the day-care centers indicated that dampness was very common in this subtropical region. We found a significant relationship between dampness and work-related sick building syndrome in the day-care-center workers. Furthermore, concentrations of fungi were lower in the day-care centers equipped with air conditioners/air cleaners than in centers that lacked such equipment. Also, Aspergillus was associated strongly with work-related sick building syndrome in the day-care-center workers.