Broodiness or, more precisely, incubation behaviour, results in the regression of the ovary and in lost egg production. It is a particular problem in turkeys and broiler breeders and may become more of a problem for other types of poultry if ‘welfare friendly’ husbandry systems become more widely used. Any system that allows the expression of full nesting behaviour will encourage the development of broodiness. The incidence of broodiness can be reduced in three ways: changing the genotype, manipulating the environment and by administering veterinary products to alter hormone function. The first two methods are generally employed, but are costly. While the third approach has not proved to be commercially viable, the situation may change. Recent advances in understanding the hormone control of broodiness have led to the identification of two novel potential veterinary products for immunization against broodiness. The first is based on the observation that an increase in the secretion of the pituitary hormone, prolactin, causes broodiness. The prolactin gene of the domestic fowl has been cloned and used to produce recombinantderived prolactin. This has been used successfully to immunize domestic fowl against broodiness, without compromising a high rate of egg laying. The second immunological approach is based on the identification of the avian prolactin releasing hormone as vasoactive intestinal polypeptide (VIP). This 28-amino acid neuropeptide was originally isolated from the gut. Immunization against VIP suppresses prolactin secretion and inhibits the development of broodiness while maintaining a high rate of egg laying. It is concluded that two novel immunogens – recombinant-derived prolactin and vasoctive intestinal polypeptide – are effective in suppressing broody behaviour and are available for further development as practical veterinary products.