Binding of multivalent lectins to cell surfaces leads to aggregation and cross-linking of glycoprotein and glycolipid receptors which, in turn, is associated with a variety of biological signal transduction process including mitogenesis. We have recently demonstrated that the interactions of multivalent lectins with naturally occurring and synthetic branch chain oligosaccharides leads to the formation of homopolymeric lectin-carbohydrates cross-linked complexes, even in the presence of mixtures of the molecules. Glycoproteins have also been shown to form homoaggregated cross-linked complexes are crystalline and have been analyzed by electron microscopy and X-ray crystallography. The results reveal a new dimension of specificity in the interactions of lectins with glycoconjugates and important insights into their structure-function properties.