The aim of this study was to determine whether exposure to fungi (molds and yeasts) among children attending a water-damaged school was reflected by the children's immunoglobulin G (IgG) response to microorganisms typical of water damage and whether the presence of these IgG antibodies was associated with respiratory symptoms and morbidity. The relationships between positive IgG antibodies and atopy, described as elevated allergen-specific immunoglobulin E (IgE) antibodies, were also examined. The study population consisted of a randomly selected group of exposed children attending a water-damaged school and a group of unexposed children of the same age. Serum samples for analyses of IgG and IgE antibodies were drawn from the children. The respiratory morbidity, the number of positive IgG antibodies to nine microorganisms indicating water damage, and IgE sensitization to common environmental allergens (Phadiatop) were studied. The mean number of positive IgG findings was significantly higher among the exposed children. The number of positive IgG antibodies did not correlate with respiratory illnesses or symptoms at the individual level even though the exposed children who had positive IgG antibodies to four or more microorganisms in the total group comparison tended to have higher respiratory morbidity. In the exposed group, a negative correlation was found between the number of positive IgG antibodies and the total value of allergen-specific IgE antibodies. As among adults exposed to microorganisms at work, IgG antibodies in children seem to be a relevant indicator of exposure to microorganisms in a water-damaged school on the group level.