Enzyme overdosage in biopolymer or complex (natural) substrates hydrolysis may decrease product yield, degree of conversion, filtration rate and prolong saccharification. Generally, enzyme efficiency may also be reduced. Synergistic action in multi-enzyme systems depends on the enzyme ratio. Using a model system of starch and fungal (Aspergillus oryzae) and bacterial (Bacillus subtilis) alpha-amylases, it was observed that the highest degree of synergistic effect (DSE) of 2.10 was achieved with the combination of 0.2 mU/ml fungal and 0.8 mU/ml bacterial alpha-amylase. This enzyme ratio was used as the initial value in the studies of enzyme overdosage. However, when the concentration of the bacterial enzyme was increased and the concentration of the fungal enzyme remained constant, the synergistic action of the enzymes decreased. As a consequence, reducing sugar released during hydrolysis goes through a maximum. The decrease in hydrolysis with enzyme overdosage depended not only on the enzyme ratio alteration, but also on the reaction time. The consequences of a decreased biopolymers degradation with enzyme overdosage in industrial processes and in animal nutrition are considered. The effect of decreased synergism in decreased hydrolysis efficiency with enzyme overdosage in relation to enzyme production and use are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.