Rational interference with disease processes by biopharmaceutical approaches requires an understanding of the biochemical basis for recognitive interactions on the level of molecules, organelles, cells and tissues. Whereas the pivotal role of nucleic acids and proteins is now well established, research efforts on a third class of information-bearing biomolecules have only recently been gaining momentum. Although progress in this field had been hampered by comparatively delayed development of adequate analytical and synthetic procedures, the presently available evidence for a physiological significance of the carbohydrate part of cellular glycoconjugates is already convincing. It includes demonstration of the participation in cell-cell and cell-matrix interactions, elicitation of biosignalling as well as cell type-specific endocytosis and intracellular routing. Within an accurately tuned molecular interplay, sugar receptors like endogenous lectins enable to transduce the informational contents of distinct oligosaccharide sequences into apparent effects. Technically, covalent attachment of such glycoligand structures to an otherwise inert carrier is proven to be valuable for unequivocal lectin detection. In histopathology these custom-made neoglycoconjugates have allowed to delineate tumour cell type-, and differentiation-associated expression of receptor sites that may in certain cases exhibit prognostic relevance. In addition to diagnostic applications, the presence of cell surface lectins can be exploited as target for drug delivery, deliberately inhibiting cell-cell interactions in infectious processes or inflammation and aiming at cell type-specific uptake of therapeuticals. Conversely, the target selectivity of tissue lectins can similarly be taken advantage of to direct the transport of any medical substance or to elicit pharmacological responses with assumed clinical benefit such as enhanced cytokine secretion. The presently dynamic development in glycobiology establishes the indispensable prerequisites to thoroughly, patiently and critically evaluate the practical efficacy of the outlined approaches.