The use of beta-glucosidase far synthesizing octyl-beta-glucoside was studied. Almond beta-glucosidase immobilized on XAD-4, glucose, and octanol were mixed at controlled water activity. A water activity of at least 0.67 was needed for synthesis of octyl-beta-glucoside, and the reaction rate increased with increasing water activity. The final yield decreased with increasing water activity. The best results were therefore obtained using a high initial water activity which was decreased during the course of the reaction. With the conditions chosen it was possible to reuse the enzyme several times.