Multiple enzyme forms of β-mannanase activity fromPolyporus versicolor were puritied to molecular homogeneity by a sequence involving DEAE Bio-Gel A chromatography, gel filtration on Sephadex G-100 and high-performance liquid chromatography using anion exchange and hydrophobic Interaction media. Overall, 7.6% of input activity was recovered in four β-mannanases, A, B, C and 2A, which were purified 112.6-, 165.5-, 143.7-and 19.9-fold respectivety. The β-mannanases were acidic proteins displaying isoelectric points from 3.75 to 4.6, molecular weights in the range of 33,900 to 57,500 and increasing hydrophobicity in the order of C>B>2A>A. Optimal pH and temperature for the hydrotysis of glucomannan by all activities were pH 5.5 and 65°C, respectively. All preparations exhibited activity after 30 min at 65°C, or after protease digestion. Although the response of individual enzymes to selected ions was variable, all β-mannanases were inhibited in decreasing order of Hg(2+)>Cu(2+)>Zn(2+)>Mn(2+). All activities functioned as endomannanases.