The glycoproteins exercise important biological functions as transport proteins, inhibitors, enzymes, hormones, complement factors, and immunoglobulins. Their chemistry is characterized by a number of rules. Thus only asparagine, threonine, or serine can carry the oligosaccharide groups; for the N‐acylglycosylamine linkage involving asparagine, the grouping Asn‐X‐Thr or Asn‐X‐Ser is always present in the peptide chain. However, practically no agreement is found in the molecular weights of the glycoproteins, their carbohydrate contents, and the relative contents of the‐various sugars. The biological significance of the carbohydrate fraction has not yet been explained, but some idea of the part played by the easily removable neuraminic acid is being formed.