Abstract Two types of extracellular (1→6)-β- D -glucanases are produced by Bacillus circulans WL-12, and these enzymes are differentiated by their ability to lyse yeast cell-walls. The non-lytic (1→6)-β- D -glucanase was isolated by a combination of Sephadex G-100, Bio-Gel P-100, and DEAE-Bio-Gel A chromatography. The purified enzyme was eloctrophoretically homogeneous and had a molecular weight of 52,000. For the substrate pustulan, the enzyme exhibited the following kinetic properties: pH, 5.0; K m , 0.83 mg of pustulan/ml; V max , 104 microequivalents of D -glucose released/min/mg of protein. Pustulan was hydrolysed by an endo-mechanism, producing D -glucose and gentiobiose as preponderant final products. The non-lytic enzyme was specific for the (1→6)-β- D -glucosidic linkage and did not hydrolyse branched, (1→3)-β- D -linked glucans containing (1→6)-interchain linkages. In contrast, the lytic (1→6)-β- D -glucanase produced D -glucose, gentiobiose, and gentiotriose as the final products of pustulan hydrolysis, and exhibited significant activity on branched (1→3)-β- D -glucans having (1→6)-interchain linkages. In these cases, the major products were gentiobiose and D -glucose, suggesting an ability of the lytic enzyme to cleave some (1→3)-linkages surrounding a (1→6)-branch-point. This latter property may explain the ability of this enzyme to weakly lyse yeast cell-walls.