For the degradation of alpha-mannans and beta-mannans Sclerotium rolfsii produces multi-enzyme systems. When cultivated in the presence of glucomannan this fungus secrets at least two beta-mannosidases (EC 3.2.1.25) and five beta-mannanases (EC 3.2.1.78). The degradation of different mannans by two purified beta-mannanases (61.2 kDa, pi 3.5; 41.9 kDa, pi 3.2) and a mannosidase (57.5 kDa, pi 4.5) is discussed in this paper All three enzymes were most stable at pH 4.5 and when they were incubated for I h at this pH and 65 degrees C they retained about 50% of their activity Mannans, gluco- and galactomannans were completely hydrolysed by the 58 kDa beta-mannosidase, which only liberated monomers from the mannans. The activity of this enzyme was enhanced by addition of either one of the beta-mannanases. The two beta-mannanases randomly cleaved fragments larger than mannobiose from the mannans. The K-M values of the beta-mannanases showed that galactose substituents of galactomannans seem to be required for the enzyme substrate binding, whilst acetyl groups inhibited both enzymes. Copyright (C) 1997 Elsevier Science Ltd.