Induction of mannanase, xylanase, and cellulase (endoglucanase) synthesis in the plant-pathogenic basidiomycete Sclerotium rolfsii was studied by incubating noninduced, resting mycelia with a number of mono-, oligo-, and polysaccharides. The simultaneous formation of these three endoglycanases could be provoked by several polysaccharides structurally resembling the carbohydrate constituents of lignocellulose (e.g., mannan and cellulose), by various disaccharide catabolites of these lignocellulose constituents (e.g., cellobiose, mannobiose, and xylobiose), or by structurally related disaccharides (e.g., lactose, sophorose, and galactosyl--1,4-mannose), as well as by L-sorbose. Synthesis of mannanase, xylanase, and endoglucanase always occurred concomitantly and could not be separated by selecting an appropriate inducer. Various structurally different inducing carbohydrates promoted the excretion of the same multiple isoforms of endoglycanases, as judged from the similar banding patterns obtained in zymogram analyses of enzyme preparations obtained in response to these different inducers and resolved by analytical isoelectric focusing. Whereas enhanced xylanase and endoglucanase formation is strictly dependent on the presence of suitable inducers, increased levels of mannanase are excreted by S. rolfsii even under noninducing, derepressed conditions, as shown in growth experiments with glucose as the substrate. Significant mannanase formation commenced only when glucose was exhausted from the medium. Under these conditions, only very low, presumably constitutive levels of xylanase and endoglucanase were formed. Although the induction of the three endoglycanases is very closely related in S. rolfsii, it was concluded that there is no common, coordinated regulatory mechanism that controls the synthesis of mannanase, xylanase, and endoglucanase.