There is an increasing prevalence of antibiotic-resistant bacteria, which makes traditional antibiotics less effective. It is thus important to find an alternative to the use of antibiotics. Oral administration of specific antibodies is an attractive approach to establish protective immunity against gastrointestinal pathogens in humans and animals. Immunotherapy can also be used against pathogens that are difficult to treat with traditional antibiotics. Laying hens are good producers of specific antibodies. After immunisation, the specific antibodies are transported to the egg yolk from which the antibodies (IgY) can be purified in large quantities. Eggs are also normal dietary components and thus there is practically no risk of toxic side effects of IgY. Yolk antibodies have been shown in several studies to prevent both bacterial and viral infections. We have treated one patient with yolk antibodies against P. aeruginosa daily for more than eight years, which shows that it is possible to use yolk immunotherapy over long treatment periods.