Ascochyta pisi produced polygalacturonase, “polymethylgalacturonase”, arabanase, ß-glucosidase, a-galactosidase and ß-xylosidase when cultured on washed cell walls isolated from pea leaflets. Polygalacturonase accounted for 78% of the detected enzyme activity and was separated into an exo- and endopolygalacturonase by cation exchange chromatography. The partially purified endopolygalacturonase, mol. wt=48 000, was inhibited by a protein, mol. wt=42 000, extracted from pea (Pisum sativum) leaflets. Of the other enzymes, only “polymethylgalacturonase” was inhibited by this protein. Between 70 and 90% of the endopolygalacturonase inhibitor in pea leaflets occurred as a soluble protein and the remainder was bound to the cell wall. The soluble and cell wall bound forms of the inhibitor were distinguishable by cation exchange chromatography. It was calculated that sufficient soluble inhibitor was present in the tissue to protect it from significant amounts of A. pisi endopolygalacturonase.