Abstract Trichoderma pseudokoningii grown on Vogel's medium supplemented with cellobiose as the carbon source yielded the highest amounts of extracellulararyl-β-glucosidase with an initial medium pH of 5.0 and incubation at 27°C in stationary culture. When the distribution of enzyme activity was determined in an exponential phase culture, the bulk of the enzyme activity was distributed in the extracellular and cell debris fractions, while in late stationary phase the former fraction increased to 65.6% of the total enzyme activity. At all times the cytosol contributed only a negligible fraction. When cellulosic substrates were used, the major portion of the enzyme appeared in the extracellular fraction at all stages of growth. The repressive effect of glucose on extracellularβ-glucosidase activity was apparent and synthesis and release of enzyme activity resumed after its depletion. The glucose effect in essence may be related to the adverse effect of low pH on the integrity of the enzyme as a decline in pH of the medium in early stages of growth usually coincided with very low yields of extracellular and cytosolic enzyme activity.