Farmers are exposed to high levels of organic dust with a high content of bacteria, fungi and endotoxins. The main exposure takes place during the many hours of work in closed animal confinement buildings, and working in swine confinement buildings gives the highest exposure. Corresponding to this, farmers have a high prevalence of respiratory symptoms and cross-sectional studies show evidence of airways obstruction. Swine farming seems to be an important risk factor for this in the farming community. Allergy plays a minor role in the development of symptoms, the most important allergy being towards storage mites. Longitudinal studies suggest that exposure to high concentrations of organic dust is associated with an accelerated decline in forced expiratory volume in one second.