The extracellular mannanase and endoglucanase activities of Trichoderma harzianum E58 were followed during growth of the fungus on 1% (w/v) mannose, Avicel, locust bean gum, konjac powder or the water-soluble fraction from stream-treated white spruce (SWS). Peak galactomannanase activities of 0.60 IU/ml and 0.66 IU/ml were detected in culture filtrates after 6–8 days growth on locust bean gum and Avicel respectively. When SWS or konjac powder were used as substrates, lower but relatively constant levels of activity were detected between 2 and 11 days of growth. Growth of the fungus on mannan-rich locust bean gum resulted in the highest specific glucomannanase and galactomannanase values. Although growth on 1% mannose failed to induce any mannanase activity, when 0.5% galactomannan was added with mannose, mannanase activity was detected in the culture filtrate. This indicated that mannanase production was not repressed in the presence of mannose. Samples were taken from each culture at the time of maximum galactomannanase activity. A protein profile obtained by isoelectric focusing was followed by a zymogram overlay to detect bands exhibiting galactomannanase, glucomannanase and endoglucanase activities. Several bands showed mannanase and endoglucananase activity. One band at pI 6.55 revealed both gluco- and galactomannanase activity and was free of detectable cellulase activity.