In a 5-year follow-up study of 88 animal exposed laboratory technicians, the incidence of laboratory animal allergy (LAA), lung function, and the development of allergy test reactivity were investigated. Only two individuals developed test positive LAA rhinitis during the follow-up period. Furthermore, one subject who had previously had LAA rhinitis developed LAA asthma. In the remaining subjects the results of skin prick tests against laboratory animals and environmental allergens, total serum IgE levels, and lung function were unchanged. Atopy defined as parental and childhood allergy, raised total serum IgE levels, and positive skin prick tests against nonanimal environmental allergens and nonlaboratory animals (dog and horse) were risk indicators for development of test positive LAA asthma. The low incidence of LAA during the 5-year follow-up is interpreted as a result of an early LAA development in atopic subjects.