A 3.5 gram quantity of β-(1→4)-glucan cellobiohydrolase C was purified from a commercial Trichoderma viride culture filtrate preparation, Meicelase P. Compared to the A and B forms, the C form of the cellobiohydrolase is present in the crude enzyme preparation in greater quantity and has a higher affinity for microcrystalline cellulose at pH 5. The C form was separated from the other forms by adsorption on a cellulose column, Following elution from the column, the cellobiohydrolase C was separated from other cellulose-adsorbed proteins by a batch separation on DEAE-Sephadex. The cellobiohydrolase C bound to the anion exchange at pH 5.0 is homogeneous by disc gel electrophoresis and identical to the "C₁" enzymes, F-II cellulase and hydrocellulase C, purified previously in this laboratory. Purified cellobiohydrolase C has an E₂₈₀^1% = 14.2and degrades both microcrystalline and phosphoric acid-swollen cellulose to cellobiose at the rates of 213 and 738 nmoles minute⁻¹ mg protein⁻¹, respectively. The cellobiohydrolase C contains 30.0, 5,5, 2,7 and 3.9 moles of mannose, glucose, galactose and glucosamine, respectively, per mole of enzyme (molecular weight 55,000). Methylation analysis of cellobiohydrolase glycopeptides indicates an average carbohydrate chain length of two residues. Consistent with the idea of several short carbohydrate chains is the release by alkaline borohydride treatment of cellobiohydrolase C of 89% of the neutral carbohydrate which is bound through an average of 19.4 0-glycosidic linkages to serine and threonine per molecule of enzyme, Glucosamine was not released from the protein by alkaline treatment suggesting a 4'-N-(2-acetamido-2-deoxy)-β-D-glucopyranosyl-L-asparagine linkage, Such an N-glycosidic linkage is consistent with the results of fractionation of the cellobiohydrolase glycopeptides by high voltage paper electrophoresis, filtration and paper chromatography which demonstrated that the glucosamine residues and the majority of the neutral carbohydrate are bound in different oligosaccharide chains. Only half of the glucosamine residues were destroyed by periodate oxidation pointing to the possible existence of both substituted di-N-acetylchitobiose units such as those found in other glycoproteins and unsubstituted single residues of glucosamine bound to the asparagine residues. Analysis of alkaline borohydride-released carbohydrate by high pressure liquid chromatography demonstrated that an average enzyme molecule contains 10,9 mono-, 2,0 di-, 4.9 tri-, and 1.2 tetra- and 0.4 pentasaccharide chains, The base stability of the linkages between the neutral monosaccharide residues in the chains and the destruction of all neutral carbohydrate periodate suggests that the (1→2) linkage is present but does not rule out the (1→6) linkage. Action of α-mannosidase indicates that at least some oligosaccharide chains contain α-mannose as the terminal residue, / Ph. D.