The results of skin prick test (SPT) with common aeroallergens (in 870 severely asthmatic children, average age at testing 8.1 years) were analysed and compared with the results of a questionnaire about pets and smoking habits in the children's homes during the first 6 months of life. The study indicates a possible correlation between early massive exposure to certain allergens (cat, timothy) and later development of hypersensitivity. No conclusion can be drawn about a possible role of tobacco-smoking.