In order to utilize cellulosic biomass, we need inexpensive cellulases produced on a large scale. However, enzyme quality must also be considered in order to obtain a high yield of cellulose hydrolysis. The enzymatic activity ratio (filter paper/cellobiase) appears to be strongly related to cellulase efficiency. In this work, we have determined culture conditions for which the FP/cellobiase ratio reaches the optimal values reported in the literature. For the hyperproducer mutant strain E-12 of Trichoderma reesei, microcrystalline cellulose as substrate and pH control at a constant value of pH 4.5 were determined as the best conditions. A well-balanced ratio was generally obtained with high C/N ratio in the medium and peanut cake as organic nitrogen source.