Pectic substances, largely polygalacturonic acid or its methyl ester, are found in the primary cell walls of plants and in the middle lamella. Enzymes from plants, fungi, and bacteria degrade pectic substances and cause plant tissue maceration by esterase action on the methyl ester groups or by glycosidase or lyase action on the polygalacturonate chain. Numer ous enzymes are distinguished from one another by mecha nism (hydrolysis or trans elimination), specificity (pectin, polygalacturonate, oligogalacturonates, Δ4:5 unsaturated oligogalacturonates), action pattern (endo or exo), and stimu lation by cations. Pectic enzymes are used commercially in producing fruit juices and wines. Fundamental proper ties of the enzymes are discussed with reference to their applications in food processes. This review is primarily concerned with fundamental properties of the A pectic enzymes with some reference to their role in nature and to their applications in food processing. Because of the vast amount of literature in this field the reader is directed to other articles and books on the chemistry of pectic substances and the enzymes which degrade them Pectic substances are found in the tissues of higher plants where they have an important structural role. They are deposited in the primary cell wall during the early stages of growth and in the middle lamella where they act as "intercellular cement." The enzymatic breakdown of pectic substances in the middle lamella leads to plant tissue maceration. There fore the enzymes that degrade pectin are involved in natural processes such as the ripening of fruit (22, 23), abscission of leaves and plant organs (24), invasion of tissues by plant pathogens (6), and in the spoil age of fruits and vegetables ( 25, 26, 27 ). They are essential in the rapid decay of dead plant material and undoubtedly assist in recycling carbon (1-21).