Carbohydrates attached to proteins and lipids characteristically display complex and heterogeneous structures. However, it is becoming increasingly clear that carbohydrates with definite biological functions also exhibit unique structural features. A number of glycoproteins and glycolipids have been shown to bear oligosaccharides containing sulfate. Often, addition of a sulfate moiety turns a relatively common structural motif into a unique carbohydrate with the potential to be recognized by a specific receptor or lectin. This is clearly the case in three systems in which sulfated oligosaccharides have been shown to play a well-defined biological role: 1) control of the circulatory half-life of luteinizing hormone, 2) symbiotic interactions between leguminous plants and nitrogen-fixing bacteria, and 3) homing of lymphocytes to lymph nodes. The rapidly growing list of glycoproteins and glycolipids identified as bearing sulfated oligosaccharides suggests that sulfated carbohydrates play important biological...