The effects of cultivation temperature, aeration rate, and agitation speed on the production of beta-mannanase by Bacillus licheniformis NK-27 in a batch fermenter were investigated in this study. Results revealed that temperature was the most significant factor in terms of its effect on beta-mannanase production. It influenced beta-mannanase production by affecting the other parameters including bacteria growth, pH, dissolved oxygen, total and reducing sugars. Agitation speed and aeration rate could affect dissolved oxygen concentration which in turn affected cell growth and beta-mannanase production. A maximum beta-mannanase activity of 212.0 U ml(-1) was attained in 36 It of cultivation when aeration rate, agitation speed, and temperature were controlled at 0.75 vvm, 600 rpm, and 30 degreesC, respectively. The maximum beta-mannanase activity in the fermenter was close to that obtained from the shake flask fermentation study (198.2 U ml(-1)). However, the duration of fermentation cycle in the fermenter study was shorter than the corresponding duration obtained from the shake flask experiment by 12 h.