Since its inception in 1968, affinity chromatography has helped solve an increasing number of problems in the biomedical sciences. By this technique, a large number of enzymes have been purified to homogeneity. Many previously unrecognized isoenzymes have been discovered. And the method has been used to solve problems as diverse as the mechanisms of enzyme action, the nature of cell interactions, the mode of immunological and hormone-receptor actions, and the treatment of diseases.