An acid hydrolysate was prepared by a procedure chosen for retaining more oligosaccharides to improve the cellulase-inducing capability when used as Substrate in the fungal fermentation for cellulase production. The effect was evaluated with continuous culture of Trichoderma reesei Rut C30 at the dilution rates of 0.03-0.08 h(-1). The specific cellulase production rates were found to be relatively constant at 8.9 +/- 0.3 (FPU/g dry cells-h), except for the lower rate, i.e., 7.2 (FPU/g-h), at the lowest dilution rate investigated (0.03 h(-1)). The former value was slightly higher than the rate obtained with a lactose-based medium, i.e., 8.2 (FPU/g-h). The maximum specific cell growth rate supported by the hydrolysate-based medium was 0.096 (h(-1)) and the apparent cell yield increased from 0.44 to 0.57 (g dry cells)/(g consumed reducing sugars) with increasing dilution rates. The best-fit maximum/ideal cell yield (without endogenous metabolism) was 0.68 (g/g), the endogenous substrate consumption rate was 0.023 (g reducing sugars)/(g city cells-h), and the specific cell death rate was 0.016 h(-1). (C) 2009 Elsevier Ltd. All rights reserved.