Abstract: The invention relates to a method and apparatus for pre-hatch avian embryo sex determination. In particular, the invention relates to a non-invasive method and apparatus for in-ovo determining the sex of avian species while in the egg and allowing to sort the eggs into groups consisting primarily of either male or female embryos. The method comprises the steps of introducing into the egg an antibody designed to match with a sex specific antigen on the embryo, which antibody is labelled, allowing the labelled antibody to migrate to and bind with the sex specific antigen on the embryo, detecting binding of the labelled antibodies on the embryo using detection means positioned outside of the egg.