The extracellular endo-beta-1.4-glucanase activity of Bacteroides succinogenes S85, grown on filter paper, was poorly stimulated by cysteine, slightly inhibited by cellobiose, but strongly inhibited by ethylthiomercuribenzoate. Active fractions against hydroxy-ethylcellulose and milled filter paper were eluted from a polyacrylamide gel filtration column with an apparent molecular weight of 60,000 daltons.