Background. The presence of horse allergen in public places is not well-known, unlike for instance cat and dog allergens, which have been studied extensively. The aim was to investigate the presence of horse allergen in schools and to what extent the influence of number of children with regular horse contact have on indoor allergen levels. Methods. Petri dishes were used to collect airborne dust samples during one week in classrooms. In some cases, vacuumed dust samples were also collected. All samples were extracted, frozen and analysed for Equ cx content shortly after sampling, and some were re-analysed six years later with a more sensitive ELISA assay. Results. Horse allergen levels were significantly higher in classrooms, in which many children had horse contact, regardless of sampling method. Allergen levels in extracts from Petri dish samples, which had been kept frozen, dropped about 53% over a six-year period. Conclusion. Horse allergen was present in classrooms and levels were higher in classrooms where many children had regular horse contact in their leisure time. This suggests that transfer of allergens takes place via contaminated clothing. Measures should be taken to minimize possible transfer and deposition of allergens in pet-free environments, such as schools. 1. Introduction In Sweden, horseback riding has become increasingly popular and is today practiced by 6% of the population, of which the majority are living in densely built-up areas. A recent survey by the Swedish Board of Agriculture estimated the number of horses to be approximately 363.000 in 2010, an increase of 10–20% since 2004 [1]. Most of the horses (75%) are located in city areas and adjoining rural areas and as a consequence, more stables are integrated with built-up areas. In an attempt to protect susceptible subjects from undesirable exposure to horse allergen, a Swedish report from the Ministry of Health and Social Affairs, in 1989, recommended a distance of at least 500？m between public buildings and homes and places where horses are kept on a regular basis [2]. This recommendation has raised a debate around the issue of whether the level of exposure to horse allergen in the surroundings of stables is different compared to exposure occurring elsewhere, for instance in public environments such as schools. In order to investigate the airborne horse allergen dispersal, a few studies have been performed using different sampling techniques to assess horse allergen levels at various distances from stables and horse tracks [3–5]. The results show that horse allergen levels
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