The high levels of maltose produced by the maltogenic alpha-amylases from Penicillium expansum and Aspergillus oryzae may be explained by the participation of multimolecular reactions. Both enzymes catalyze transglycosylation reactions during the concentration-dependent degradation of maltooligosaccharides produced on hydrolysis of starch. The significantly higher yields of maltose achieved with the P. expansum alpha-amylase, compared to the A. oryzae enzyme, appear to be due to the mechanism of action of P, expansum on maltotriose. The A. oryzae enzyme only switches from unimolecular to multimolecular events at high concentrations of the trisaccharide. The P. expansum alpha-amylase, however, catalyzes reactions other than simple hydrolysis at all concentrations of maltotriose tested, resulting in the production of maltose in excess of glucose from this major intermediate of starch hydrolysis.