Exposure to various factors from the indoor environment on respiratory health of 470 Dutch primary school children was studied. We investigated which of the factors, such as home dampness, passive smoking, unvented kitchen geysers, or pets, affected children's respiratory health the most, and whether airway sensitivity to these indoors exposures differed between boys and girls. Information on respiratory morbidity and characteristics of the housing was obtained by a written questionnaire, completed by the parents of the children. Lung function of the children was measured at school, by forced oscillation technique (FOT) and spirometry. In boys, all investigated lung function parameters were significantly affected by exposure to passive smoking during the child's entire life. Although mostly nonsignificant, all of the reported asthma-like symptoms were related especially to maternal smoking, with a trend of a dose-response relationship. Furthermore, damp stains (P < 0.05) and mold growth (ns) were associated with chronic cough and with small but significant impairments in part of the lung function parameters. No consistent patterns were observed with unvented kitchen geysers and pets. Although passive smoking (cumulative dose) in girls was also associated with lung function impairments, the effects were smaller than those in boys and not all significant. Associations between the asthma-like symptoms and the dose of maternal and paternal smoking also were less consistent. Furthermore, no associations were found with the dampness indicators and with pets, but unvented kitchen geysers were significantly related to impairments in some of the impedance indices. This study shows detrimental effects of several indoor factors on the prevalence of chronic respiratory symptoms and lung function in children, which are most pronounced for passive smoking, and somewhat less pronounced for dampness and the presence of unvented kitchen geysers. Airway sensitivity to these exposures appeared to be higher in boys than in girls.