Floor dust was collected in the wintertime from the homes of 61 children sensitized to house dust mites, 57 children with sensitization to other aeroallergens, and 57 nonatopic control children. The dust was cultivated and microfungal growth was identified microscopically. Indoor humidity was measured, and condensation on windowpanes was registered during 1 winter week. Housing and sociodemographic and symptom data were obtained by a questionnaire. Penicillium, Alternaria, and Cladosporium were the three most common microfungi. The mean total number of colony-forming units per 30 mg of dust was significantly lower in the homes of the two atopic groups than in homes of the control group, which may be a result of allergen-sanitation measures. High colony-forming unit counts appeared to be related to damp housing. Weak associations were found between the occurrence of viable fungi in dust and allergic symptoms among the house dust mite-sensitized children. However, no consistent association between viable mold growth and sensitization to molds was observed. The health implications of indoor fungal exposure still remain unclear.