INTRODUCTIONThe technique presented this protocol is ideal for obtaining an overall, three-dimensional picture of the distribution of an antigen in embryos from the prestreak stage to ~10.5 dpc (days post-coitum). The embryos are fixed and permeabilized so that antibodies can penetrate all of the tissues. However, antibodies will not penetrate the embryo completely if it is too large, and so it is better to dissect specific organs (e.g., brain, lungs, and gut) and process them separately.