An easily scaled-up technique has been designed to purify beta-mannanase from Bacillus licheniformis. Using flocculation, ultrafiltration and ion-exchange chromatography, the enzyme was purified 33-fold with a final recovery of 47% and a specific activity of 4341 U mg(-1) protein. The enzyme had maximum activity at 60 degrees C and pH 7.0. It was stable at 50 degrees C and pH 6.0 for 6 h, but lost all of its activity when held at 70 degrees C and pH 6.0 for 1 h.