Molecular chaperones and especially chaperonins are primarily known as special members of the family of heat shock proteins which participate in folding, assembly, transmembrane transport and degradation of a wide variety of cellular proteins both in prokaryotes and eukaryotes. The multifunctional character of chaperones underlies their involvement in many diseases. One of their functions is binding to polypeptides lacking a rigid tertiary structure, i.e., to those with many exposed hydrophobic amino acids. The current review is focused on interaction of polypeptides of this type with GroEL, the best-studied Escherichia coli chaperonin. The literature data on driving forces of their interaction, localization of substrate polypeptides on the GroEL surface, and the effect of GroEL ligands on its interaction with substrate polypeptides are considered. Some biotechnological applications of this event are also discussed.