The ISAAC (International Study of Asthma and Allergy in Childhood) was founded in 1990 in order to maximise the value of epidemiological research into asthma and allergic diseases, to describe the prevalence of asthma and allergic disease in children living in different locations, to make comparisons within and between countries, to provide a framework for further etiological research and to find prevention strategies. We analysed a sub-sample of a population-based study (1995 to 1997) in Upper Austria. The aim of our study was to investigate the influence of indoor risk factors on wheezing in children 6-9 years old. Our calculations were based on the results of a questionnaire answered by parents about their children's indoor environment at home. Smoking of the mother during pregnancy and/or during breastfeeding (OR 1.28; 95% CI 1.08-1.48), smoking of the mother at the present time (OR 1.25; 95% CI 1.12-1.41), a bird (OR 1.40; 95% CI 1.06-1.85) or rabbit (OR 1.37; 95% CI 1.03-1.82) as a domestic pet, synthetic bedding (OR 1.33; 95% CI 1.18-1.49) and dampness or mould at home (OR 1.43; 95% CI 1.24-1.65) are associated with a significantly increased risk of childhood wheezing in the last 12 months. Other variables such as "smoking of the father", "cooking with gas", "gas central heating" and other "pets" do not achieve statistical significance.