Pure saturated and unsaturated oligogalacturonic acids, including unsaturated monogalacturonic acid, were isolated and characterized. Their ultraviolet absorbance at 232 run, and their reactivities in the periodate thiobarbituric acid test and carbazole tests were studied. From these compounds methyl oligogalacturonates were prepared, which were used as model substrates.Pectin lyases (EC 4.2.99.8; poly-α-1,4-D-methyl-galacturonate lyase) were found to be very common in commercial 'pectinase' preparations. From each of three 'pectinase' preparations a pectin lyase was isolated free of other pectolytic enzymes. Their pH optimum, pH stability, isoelectric point and activation energy were determined. Information on the action of the enzymes on pectins with various degrees of esterification ( DE ) was obtained by kinetic studies, by determining the extent of degradation and by analysing the composition of the reaction mixtures. The breakdown mechanism on pectin and pattern of action on methyl oligogalacturonates was studied. Divalent cations were found to activate pectin lyase activity, their activation depended on the pH and DE. Literature on the isolation and characterization of oligogalacturonides and on pectin degrading enzymes is reviewed.