Six collagenases present in the culture filtrate of Clostridium histolyticum have been purified to homogeneity. Chromatography over hydroxylapatite, Sephacryl S-200, and L-arginine-Affi-Gel 202 removes the brown pigment and the great majority of the contaminating proteinases active against casein, benzoyl-L-arginine ethyl ester, and elastin. Reactive Red 120 dye ligand chromatography subdivides the collagenases, which have very similar physicochemical properties, among four fractions. The final purification is achieved by chromatography over DEAE-cellulose and SP-Sephadex. All six collagenases, designated alpha, beta, gamma, delta, epsilon and zeta by the order of their purification, are highly active against collagen and devoid of other proteolytic activities. Each exhibits a single band on sodium dodecyl sulfate-polyacrylamide gels. Two distinct subspecies of the alpha and gamma enzymes have been isolated, which have the same molecular weight and activity but different isoelectric points. There is some less pronounced microheterogeneity for the other collagenases. On the basis of their activities toward native collagen and the synthetic peptide 2-furanacryloyl-L-leucylglycyl-L-prolyl-L-alanine (FALGPA), the six collagenases are divided into two classes. Class I collagenases (alpha, beta, and gamma) have high collagenase activity and moderate FALGPA activity while the class II collagenases (sigma, epsilon, and sigma) have moderate collagenase and high FALGPA activities. The relationship between these six collagenases and other reported to have been isolated in the literature has also been examined.