The cell wall structure of plants is composed of a complex matrix of polysaccharides and protein. Controlled alteration of the cell wall matrix by enzymic hydrolysis allows cell enlargement in compliance to cell turgor. To investigate the metabolic events involved in cell elongation, proteins were extracted and characterized from Zea mays seedling cell walls. Wall proteins were extracted with lithium chloride and separated into several major fractions by using cation exchange chromatography. One fraction, which was not bound to the cation exchange column, elicited antibodies which inhibited auxin induced growth. Active subfractions were further resolved by using gel filtration, identified by bioassay, and characterized by immunoprecipitation. The active protein(s) were acidic in nature and had no hydrolytic activity against polysaccharides in isolated cell walls;A separate fraction investigated, bound tightly to the cation exchange column and contained endo-(beta)-D-glucanase activity. The endo-(beta)-D-glucanase was purified extensively using ion exchange and gel filtration chromatography. The enzyme is characterized by a molecular weight of 20-25 kD, an isoelectric point of greater than pH 9, and thermal stability to temperatures of 50 C. Hydrolytic activity against model substrates indicated a high specificity for (beta)-1,3;1,4-D-glucans. No hydrolysis of (beta)-1,3-D-glucans was observed. Hydrolytic activity against specific mixed-linked glucans appeared to be restricted to the hydrolysis of a (beta) 1--4 glucosyl linkage within regions enriched in (beta) 1--4 and (beta) 1--3 linkages. This restricted hydrolysis resulted in the release of uniform products containing 60 to 70 glucose residues. The endo-(beta)-D-glucanase has a putative role in the degradation of the mixed linked (beta)-D-glucan molecule during auxin induced growth.