Intact, developing chick embryos (stages 9+ to 14) incorporate sugars from sugar nucleotides in patterns which vary according to the sugar nucleotide used, the area of the embryo, and the age of the embryo. Radioautographs of the notochord-somite-lateral plate mesoderm vicinity, the optic vesicle-skin ectoderm junction, and the area vasculosa are presented. It is possible that these patterns represent localized cell surface glycosyltransferase-glycosyl acceptor complexes. However, other possibilities have not been ruled out. The potential role of enzyme-substrate complexes in intercellular interactions is discussed.