A 2(3) central composite design (CCD) was applied to determine the optimal conditions of cultivation time, aeration and temperature to xylanase and mannanase production by Bacillus circulans BL53, a strain isolated from the Amazonian environment. The results suggest that xylanase production by B. coagulans BL53 is higher at a moderate cultivation aeration and at low temperatures and following CCD modeled conditions, we were able to increase 2.5-fold enzyme activities previously obtained and published by our group. For mannanase, the results showed that production was increased at higher aeration rate, and lower temperature. The highest enzymatic activity experimentally obtained according to the CCD was 3.7-fold higher than previous conditions employed. The predicted optimal parameters were tested in the laboratory and the final xylanase and mannanase activities obtained were very close to the predicted value (0.928 U mg(-1), predicted; 0.953 U mg(-1), tested; and 0.544 U mg(-1), predicted; 0.540 U mg(-1), tested, respectively). Our results show that optimization of the enzymes production is an useful way of obtaining concentrated enzyme extracts from solid-state cultivation of industrially important microorganisms. (c) 2005 Elsevier Inc. All rights reserved.