To clarify the association between indoor environmental factors and child health problems, epidemiological surveys of fourthand fifthgrade children were conducted in Japan. A case-controlled field study involving 209 houses was conducted during the winter and the rainy season. Chemical compounds, fungal index, airborne fungi, and microorganisms in house dust were analysed. The association between each exposure and children's health was examined. Results indicate that the mean formaldehyde concentration in the case group was significantly lower than that of the control group in the winter (p<0.01). Fungal index, airborne fungi and microorganisms in house dust tended to be higher in case group than in the control group for both seasons.