Using 74 serological test strains for different Klebsiella K antigens as propective hosts, 50 new bacteriophages were isolated, the particles of which catalyze host capsular glycan depolymerization. As seen under the electron microscope, these viruses most often belong to Bradley's morphology group C (36 cases), occasionally to group B (11), and rarely to group A (3); they all carry tail spikes (or thick fibers) with which, presumably, the glycanase activity is associated. Employing the same set of Klebsiella strains, the host range of a total of 55 such bacteriophages was tested and 28 cross-reactions (host capsule depolymerization and plaque formation at a relative efficiency of plating ⪕ 10 5) were detected; in addition, one abortive infection (host capsule depolymerization without plaque formation) was found. The viral depolymerases thus proved to be very specific (33 cross-reacting with no, 18 with one, 2 with two, and 1 each with three or four heterologous polysaccharides). For further characterization of the over 80 phage-catalyzed depolymerization reactions thus identified, the purified virus particles were incubated with the isolated bacterial capsular polysaccharides, and the oligosaccharides produced were analyzed for reducing end sugar (glucose, galactose, mannose, fucose, or rhamnose), and for size (mainly one to three repeating unit oligosaccharides in about 85% of the cases). In those 49 phage-host systems, where the primary structures of the substrate polysaccharides were known, the reducing end sugar analyses led to unequivocal (36 reactions) or tentative (13) identifications of the phage enzyme susceptible glycosidic linkages, and hence to the following general conclusions: (I) in most cases cleavage occurs on either side of the (a) sugar unit carrying the negative charge(s), but reducing glycuronic acids are not produced; (II) most often, the reducing end sugar formed is substituted at position 3; (III) in the majority of cases, β-glycosidic linkages are hydrolyzed; (IV) in most polysaccharides which are acted upon by several phage enzymes, the same glycosidic bonds are split by the different agents.