The comparison of maximal endoglucanase activity produced by A.niger in SSF with those reported for other cellulase producing microorganisms (Table 5) showed that the fungus investigated in this work compared favourably with most of those microorganisms. The characterization of cellulase enzymes poses special problems (substrate insoluble and structurally variable, multicomponent enzymatic complex) to the enzymologist, which are rarely encountered in the study of other enzymes. In the face of these difficulties it is understandable that the comparison of cellulase activities produced by different laboratories is not readily made in a quantitative manner. On the other hand, the endoglucanase measurements do not reflect the true activity for hydrolyzing crystalline cellulose. The ability of Trichoderma reesei and its mutants to produce cellulases is considered in measuring the enzyme concentration FPU (filter paper activity): ml (Esterbauer et al., 1991).