The use of infrared spectroscopy to determine the gender of young birds shows that it is a fast and accurate method with the potential to be used by the breeding industry and many other fields. Second, results of a pilot study show that infrared spectroscopy also provides an approach to determine the gender of fertilised unincubated eggs. The difference in the RNA content, as well as the amount of DNA between the Z and W sex chromosomes, are very sensitive markers for spectroscopybased sexing. In the future, these is a strong possibility that infrared spectroscopy can be used for an in ovo gender determination which could save millions of unwanted male layer chicks from being killed shortly after hatching.