Immune responses to allergens in young children include both Th1- and Th2-like immunity, which may regulate the secretion of immunoglobulin (Ig) G subclass antibodies differently. The time, route and level of exposure to an allergen may be decisive with regard to whether sensitization or tolerance will ensue. To study this, we investigated the development of IgG subclass antibodies to food and inhalant allergens during childhood. The study group comprised a cohort of 96 children participating in a prospective study. IgG subclass antibodies to ovalbumin, Bet v 1 and cat dander were analyzed at birth, 6 and 18 months and 8 years by ELISA. IgG1 and IgG3 subclass antibodies to ovalbumin peaked at 18 months and then declined up to 8 years of age, whereas antibodies to the inhalant perennial allergen cat, but not the inhalant seasonal allergen birch, increased with age. Exposure to cat and birch tended to be associated with high antibody levels to those allergens, whereas antibody levels to ovalbumin were not related to exposure to egg. The presence of positive skin prick tests and circulating IgE antibodies correlated with high levels of IgG subclass antibody responses to the allergens. Atopic symptoms were associated with high levels of IgG subclass, particularly IgG4, antibodies to the allergens. The difference in antibody levels between atopic and non-atopic children was most marked at 6 months for ovalbumin. For the seasonal inhalant allergen birch, the difference was apparent from 18 months, whereas a difference in antibody levels to the perennial inhalant allergen cat was already present at 6 months. In conclusion, IgG subclass antibodies to food allergens peak in early infancy and are then down-regulated, whereas antibodies to the inhalant perennial allergen cat, but not the inhalant seasonal allergen birch, increase with age. Atopy is associated with high levels of IgG subclass, particularly IgG4, antibodies to allergens, supporting a deviation of the immune system towards Th2-like responses in atopic children.