The applications of affinity chromatography are becoming increasingly more varied, as the method makes use of specific interactions of biologically active substances. It is used with advantage—mainly for the isolations of a wide range of compounds. It is used in studies of various systems, from separations of low-molecular-weight enantiomeric pairs to the elimination of undesirable substances from living organisms. By affinity chromatography—for example, D,L-tryptophan can be separated. Using the specific isolation of labelled peptides, the peptides of the active site of an enzyme, of the binding site of antibodies or the site of the peptide chains on the molecule surface can be determined. Affinity chromatography can be used to study the possibility of substituting natural peptide chains of enzymes with various modified synthetic peptides. The active sites of enzymes or antibodies, the binding properties of subunits, the specificity of enzymes toward various inhibitors, the complementarity of nucleic acids, the interaction of nucleotides with peptides, the effect of the presence of various substances on the formation of specific complexes, etc., can be studied by affinity chromatography. The problems of the mechanism of enzymatic activity can be studied on the basis of the course of affinity chromatography or the molecular structures of—for example, fibroblast or leucocyte interferons can be judged. The application of immunosorbents in solid-phase radioassay and in immunofluorescence assay is currently becoming an independent branch of immunology. The application of affinity chromatography for the elimination of undesirable substances from the blood of living organisms is also being investigated.