Mac-2 is a member of the S-(soluble) lectin family. Its identification and isolation from a wide variety of cell types and tissues suggest a diversity of roles in various biological systems. The key points to be made are that Mac-2, and the S-lectins in general, by virtue of their recognition of a variety of carbohydrate structures expressed on different glycoproteins, are well placed to exert discrete biological effects according to the distribution of those glycoproteins in tissues and their differential patterns of glycosylation according to developmental status and cell type. In this regard, the lectins are fundamentally different in character to other effector molecules that in general bind to specific receptors to trigger single signal transduction events.