The review deals with the new area in biorecognition--the carbohydrate-carbohydrate interaction. Seven experimental approaches are described that were used for detecting and investigating this phenomenon, with special reference to its mechanism and peculiarities, particularly, in comparison with other types of molecular interactions; some historical aspects are also considered. The whole body of experimental evidence published on carbohydrate-carbohydrate interaction by the end of 1995, is reviewed. A special chapter is dedicated to intercellular adhesion mediated or initiated by carbohydrate-carbohydrate recognition. The main peculiarities of carbohydrate-carbohydrate interaction are as follows. Monovalent interaction is so low affinity that it cannot be recorded by routine physical methods, such as NMR. However, if polyvalent ensembles of oligosaccharides (e.g., two membranes with a high density of built-in glycolipids) come in contact, one can observe a specific Ca(2+)-dependent interaction which is inhibited by either EDTA antibodies against carbohydrates or by oligosaccharides. The carbohydrate/carbohydrate-mediated cell adhesion is a rapid primary process which immediately precedes carbohydrate-lectin (selective) and protein-protein (integrin) adhesion. Le(x)/Le(x)-Mediated compactization of embrions and Gm3/Gg3 mediated adhesion of tumour cells provide illustrative examples of such intercellular contacts.