Scientists have found a way to make chickens lay the pharmaceutical equivalent of a golden egg. Helen Sang and her team, from Scotland's Roslin Institute, used a virus to genetically alter chickens so that they could produce eggs containing drugs. In two different examples the team linked the genes for human interferon beta, or a melanoma-attacking antibody called miR24, to the chicken gene sequences that control the production of ovalbumin, the protein that makes up egg white. The idea was to use the genetic signals that control the production of egg white to make sure that the drug only ended up in the egg. The team then inserted these genetic 'constructs' into an equine infectious anaemia virus (EIAV) from which all of the harmful viral genes had been removed. The modified virus was then injected into a fertilised egg, where it added the new genes to the chick developing inside. The resulting chicken then laid eggs containing the new drug, and also passed the ability to do so onto its offspring. A study of the bird's tissues also confirmed that, as the team had hoped, only the oviduct, which produces eggs, was making the drug.